Group Title: BMC Plant Biology
Title: Design and fabrication of adjustable red-green-blue LED light arrays for plant research
CITATION PDF VIEWER THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00100028/00001
 Material Information
Title: Design and fabrication of adjustable red-green-blue LED light arrays for plant research
Physical Description: Book
Language: English
Creator: Folta, Kevin
Koss, Lawrence
McMorrow, Ryan
Kim, Hyeon-Hye
Kenitz, J. D.
Wheeler, Raymond
Sager, John
Publisher: BMC Plant Biology
Publication Date: 2005
 Notes
Abstract: BACKGROUND:Although specific light attributes, such as color and fluence rate, influence plant growth and development, researchers generally cannot control the fine spectral conditions of artificial plant-growth environments. Plant growth chambers are typically outfitted with fluorescent and/or incandescent fixtures that provide a general spectrum that is accommodating to the human eye and not necessarily supportive to plant development. Many studies over the last several decades, primarily in Arabidopsis thaliana, have clearly shown that variation in light quantity, quality and photoperiod can be manipulated to affect growth and control developmental transitions. Light emitting diodes (LEDs) has been used for decades to test plant responses to narrow-bandwidth light. LEDs are particularly well suited for plant growth chambers, as they have an extraordinary life (about 100,000 hours), require little maintenance, and use negligible energy. These factors render LED-based light strategies particularly appropriate for space-biology as well as terrestrial applications. However, there is a need for a versatile and inexpensive LED array platform where individual wavebands can be specifically tuned to produce a series of light combinations consisting of various quantities and qualities of individual wavelengths. Two plans are presented in this report.RESULTS:In this technical report we describe the practical construction of tunable red-green-blue LED arrays to support research in plant growth and development. Two light fixture designs and corresponding circuitry are presented. The first is well suited for a laboratory environment for use in a finite area with small plants, such as Arabidopsis. The second is expandable and appropriate for growth chambers. The application of these arrays to early plant developmental studies has been validated with assays of hypocotyl growth inhibition/promotion and phototropic curvature in Arabidopsis seedlings.CONCLUSION:The presentation of these proven plans for LED array construction allows the teacher, researcher or electronics aficionado a means to inexpensively build efficient, adjustable lighting modules for plant research. These simple and effective designs permit the construction of useful tools by programs short on electronics expertise. These arrays represent a means to modulate precise quality and quantity in experimental settings to test the effect of specific light combinations in regulating plant growth, development and plant-product yield.
General Note: Start page 17
General Note: M3: 10.1186/1471-2229-5-17
 Record Information
Bibliographic ID: UF00100028
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: Open Access: http://www.biomedcentral.com/info/about/openaccess/
Resource Identifier: issn - 1471-2229
http://www.biomedcentral.com/1471-2229/5/17

Downloads

This item has the following downloads:

PDF ( PDF )


Full Text


0
BMC Plant Biology Central


Methodology article


Design and fabrication of adjustable red-green-blue LED light arrays
for plant research
Kevin M Folta* 1, Lawrence L Koss3, Ryan McMorrowl, Hyeon-Hye Kim2, J
Dustin Kenitz', Raymond Wheeler2 and John C Sager2


Address: 'Horticultural Sciences Department and the Plant Molecular and Cellular Biology Program, University of Florida, Gainesville, USA,
2Biological Sciences Office, Space Life Sciences Laboratory, Kennedy Space Center FL, USA and 3Dynamac Corporation, Space Life Sciences
Laboratory, Kennedy Space Center, FL, USA
Email: Kevin M Folta* kfolta@ifas.ufl.edu; Lawrence L Koss Lawrence.Koss-1@ksc.nasa.gov; Ryan McMorrow ryanmc@ufl.edu; Hyeon-
Hye Kim Hyeonhye.Kim-1 @ksc.nasa.gov; J Dustin Kenitz bltoe@ufl.edu; Raymond Wheeler Raymond.M.Wheeler@nasa.gov;
John C Sager John.C.Sager@nasa.gov
* Corresponding author



Published: 23 August 2005 Received: 31 March 2005
BMC Plant Biology 2005, 5:17 doi:10.1 186/1471-2229-5-17 Accepted: 23 August 2005
This article is available from: http://www.biomedcentral.com/1471-2229/5/17
2005 Folta et al; licensee BioMed Central Ltd.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0),
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.



Abstract
Background: Although specific light attributes, such as color and fluence rate, influence plant growth and
development, researchers generally cannot control the fine spectral conditions of artificial plant-growth
environments. Plant growth chambers are typically outfitted with fluorescent and/or incandescent fixtures
that provide a general spectrum that is accommodating to the human eye and not necessarily supportive
to plant development. Many studies over the last several decades, primarily in Arabidopsis thaliana, have
clearly shown that variation in light quantity, quality and photoperiod can be manipulated to affect growth
and control developmental transitions. Light emitting diodes (LEDs) has been used for decades to test
plant responses to narrow-bandwidth light. LEDs are particularly well suited for plant growth chambers,
as they have an extraordinary life (about 100,000 hours), require little maintenance, and use negligible
energy. These factors render LED-based light strategies particularly appropriate for space-biology as well
as terrestrial applications. However, there is a need for a versatile and inexpensive LED array platform
where individual wavebands can be specifically tuned to produce a series of light combinations consisting
of various quantities and qualities of individual wavelengths. Two plans are presented in this report.
Results: In this technical report we describe the practical construction of tunable red-green-blue LED
arrays to support research in plant growth and development. Two light fixture designs and corresponding
circuitry are presented. The first is well suited for a laboratory environment for use in a finite area with
small plants, such as Arabidopsis. The second is expandable and appropriate for growth chambers. The
application of these arrays to early plant developmental studies has been validated with assays of hypocotyl
growth inhibition/promotion and phototropic curvature in Arabidopsis seedlings.
Conclusion: The presentation of these proven plans for LED array construction allows the teacher,
researcher or electronics aficionado a means to inexpensively build efficient, adjustable lighting modules
for plant research. These simple and effective designs permit the construction of useful tools by programs
short on electronics expertise. These arrays represent a means to modulate precise quality and quantity
in experimental settings to test the effect of specific light combinations in regulating plant growth,
development and plant-product yield.



Page 1 of 11
(page number not for citation purposes)


70p7en7A7c







http://www.biomedcentral.com/1471-2229/5/17


Background
Light drives the processes of photosynthesis and plant
development, and ultimately affects crop yield. The culmi-
nation of over a century of plant photobiology research
shows that plants possess complicated photosensory net-
works that monitor and respond to a wide spectrum of
ambient light energies. The spectral sensitivity of the plant
light-sensors greatly exceeds the range of human vision, as
light effects on physiology have been observed from ener-
gies arising from the UV-B wavebands [1] into the near
infra-red [2]. This broad range of environmental informa-
tion is processed by integrated signaling networks that tai-
lor growth and development to best fit ambient light
conditions.

Light sensing pathways have been dissected through use
of narrow-bandwidth light sources. Since individual pho-
toreceptors are generally tuned to sense specific regions of
the spectrum, narrow-bandwidth irradiation allows isola-
tion of effects associated with a particular waveband. For
instance, the phytochromes mediate responses to red and
far-red light, with partial activity extended through the
green, blue and near-UV wavebands. Cryptochromes are
required for maximal response to blue and UV-A [3],
while the phototropins exhibit autophosphorylation
when stimulated with light qualities from the blue-green
interface (500 nm) to UV-C [4]. Other sensors share sen-
sory overlap with the phototropins, and at least several
other receptors remain to be characterized [5].

Narrow-bandwidth, research-quality light is typically gen-
erated using a broad spectrum source (such as an incan-
descent lamp) filtered through an infra-red heat sink and
several layers of acetate theatre filters or colored plastic.
Fluorescent lamps also are used, as they emit three princi-
ple light qualities that can be readily filtered to obtain nar-
row-bandwidth light. LED light has been used principally
in studies of phytochrome reversibility, as switchable red
and far-red LED arrays are commercially available. Many
reports have demonstrated the utility of red/far-red LED
sources in modulating phytochrome responses during de-
etiolation [6-8], modulation of root growth [9], root
greening [10] and senescence [7]. LED technology has
been incorporated into lighting regimes to modulate
plant growth and development for decades as acute sup-
plementation of sunlight (such as [11-13]) or as the basis
of plant growth in commercial chambers (as in [14]).
Additionally, LED-generated light is well-suited for small
growth chambers and other applications where a signifi-
cant fluence rate is required, but little physical space is
available for conventional lamps. The practical aspects of
LED lighting make them particularly well-suited for space
applications where light treatments need to be precise and
reliable with little heat radiation and low weight. LEDs
may also be especially useful in retrofitting incandescent


BANK 4


BANK 3


BANK 2 BANK
D C0


Ti 4
_ m 9 p


Figure I
A simplified diagram of Design I. Here 20 Norlux HEX
arrays are configured into four individual banks of five arrays
each. R, G and B are individually controllable on each bank,
allowing the use of the controller to regulate light conditions
over four independent light quality and quantity conditions.
The four banks are regulated by two independent power
supplies, actuated by two separate timers. In this configura-
tion two separate photoperiods may be tested for any set of
experimental parameters.


or fluorescent growth
applications.


chambers for terrestrial


There is a need for a light source that may facilitate plant
growth in a chamber environment, yet still allow for
dynamic variation in light quality and quantity for exper-
imental studies. Such devices may reveal interesting inter-
actions between light sensing systems. Recent findings
demonstrate that even "benign" wavebands (like green
light) have significant influence in plant physiology in
concert with red and blue light [15-17]. In this report we
detail the design and construction of a compact LED light
array for use in plant research. These light sources utilize
Norlux hex-LED arrays and are capable of delivering 0 -
150 [tmol m-2 s-1 of combined red (R), green (G), and/or
blue (B) light. The design allows precise fluence-rate con-
trol of individual wavebands, allowing growth of plants
under different combinations of light energies. These
designs are the same as those used to generate plant-
growth data in a number of recent studies of red, blue and
green light interaction [17,18]. Two designs are presented
in Figures 1, 2, 3, 4. The first is a plan that may be suitable
for use in the laboratory or classroom for fewer than one
thousand dollars. The second depicts an expandable sys-
tem that may be appropriate for large growth chambers.
Together the two plans presented represent tested and
proven designs to introduce efficient lighting to chambers


Page 2 of 11
(page number not for citation purposes)


BMC Plant Biology 2005, 5:17







http://www.biomedcentral.com/1471-2229/5/17


13.8V Supply



GndB


rRedB



=C7
Cap LM3
O.luF iE4


2 R28
-- > ^ -- 1 \ w --


R16
317 -Res]
1K


R4
P ^'RPotI
GndB 20K

GndB


Power
1 Ohm


Red SwB

RI
REDB
DB


GndB


-C10
Cap
JluF
GndB


--


Figure 2
A) The schematic of the Tunable LED controller circuit used in Design I. The controller regulates the output of four sets of
five LEDs. The schematic represents the circuit used to power one color (R, G, or B) in five separate HEX chips, and therefore
is repeated twelve times in the controller unit in this arrangement. The 5 HEX LED bank is shown from a bottom (B) and top
(C) view.








Page 3 of 11
(page number not for citation purposes)


supplyB i-


BMC Plant Biology 2005, 5:17







http://www.biomedcentral.com/1471-2229/5/17


where light quality, quantity, duration and mixture can be
readily controlled.

Results and discussion
The advent of new semiconductor technologies has
inspired a marked decrease in the price of LED-based
devices. An increased number of consumer-grade prod-
ucts have become available to the researcher, and now
these new tools may be integrated into various light-
research applications. The goal of this work is to provide
an interface between research needs and new technology.
With this, the best-available research tools may be imple-
mented by researchers without a significant investment in
development. The plans presented herein offer two
options for LED light source construction, based on the
need of an experimental illumination tool or requirement
for large-area irradiation.

LED-based lighting regimes are being adopted by munici-
palities and medical facilities for their consistent, low-
power, low-maintenance output. However, one of the
most important practical applications of this technology
is in the design for lighting regimes to support plant
growth. It is of great interest to not only to foster plant
growth, but to control plant growth. Basic plant research
has demonstrated that specific light wavebands may affect
discrete aspects of plant physiology, such as germination
[19], stem growth [20], biomass [15,21,22] and the
transition to flowering [23]. The supplementation of spe-
cific wavebands or skewing of overall spectrum may help
modulate the progression of these developmental events.
The possibility that combinatorial light regimes may help
to optimize growth and control developmental transi-
tions makes the implementation of LED technology par-
ticularly attractive to the design of controlled
environments targeted to plant production for aesthetic
applications, or applications relevant to human nutrition.
If spectral quality alone can delay or hasten the floral tran-
sition it may have profound effects on modulating the
delivery of nursery goods or perhaps affect the availability
of consumable produce in a finite, controlled environ-
ment. This attribute alone makes LED lighting a compel-
ling platform for specific plant growth routines, such as
those proposed for long-term inhabitation of space. Since
humans rely specifically on vegetative parts (like stems,
leaves and tubers) or reproductive parts (berries and
seeds) of plants for nutrition, it is critical to develop sys-
tems which impart control of the progression of plant
development to affect plant output toward the particular
needs of humans.

The implementation of narrow-wavelength LED technol-
ogy may benefit plant growth schema through supple-
mentation or complete retrofitting of existing chambers.
Its compact design may replace existing infrastructure


with long-life and consistent output. Here, antiquated
lamp systems, replete with toxic, inefficient fluors, may be
refitted with efficient light sources that require little to no
maintenance with comparable light output. Although pre-
viously unattainable without substantial engineering, the
geometry of the systems provided in this report brings
LED technology to the average plant biology laboratory.

Despite their vast advantages over conventional lighting
systems, the LED arrays described in this report offer
opportunities for improvement and expansion. Larger
installations (e.g. 100 HEX arrays) require close attention
to array density, as the fluence rate of RGB HEX LED lights
decays significantly toward the edges of the irradiation
area. Careful arrangement modified to the application
lessens the frequency of "hotspots" or other gradients of
light intensities under the light fixture. It is impossible to
eliminate all variability under the arrays under all fluence
rates and light combinations. The spacing of HEX units in
individual systems needs to be carefully tailored for the
specific application.

Another potential improvement would be to integrate
PAR sensors into the system to provide irradiance feed-
back and adjust light intensity through a computer-aided
regulatory circuit. This would allow the user to enter a spe-
cific irradiance value for the desired wavelength and
would compensate for changes in LED output that occur
over time and with temperature changes in the ambient
environment.

This system has been developed using LEDs emitting three
principal wavebands. The clear extrapolation is to add
additional LED types to generate additional spectrum cov-
erage. LEDs currently manufactured include UV, far-red
and infra-red light. From the plans presented within this
report it may be possible to develop lighting systems that
roughly approximate solar output by compounding the
effects of multiple LEDs. Such a system may prove espe-
cially valuable in optimizing plant physiology and may
have applications to human physiology as well.

The arrays described were tested for support of normal
plant developmental responses. These are most conspicu-
ous in early seedling development, as initial responses to
light are rapid, robust, and have been well characterized
[5,24-26]. Three responses to light, namely inhibition of
stem elongation (red or blue activated), stem growth pro-
motion (green activated) and phototropism (blue acti-
vated), have been extremely well characterized and may
be used to test and verify the utility of these LED arrays on
early plant developmental responses. Three assays were
conducted. First, end-point stem growth was measured in
plants grown under three fluence rates of red or blue light.
Red and blue light strongly inhibit early stem elongation


Page 4 of 11
(page number not for citation purposes)


BMC Plant Biology 2005, 5:17







http://www.biomedcentral.com/1471-2229/5/17


Figure 3
A) The components and organization of the RGB control unit used in Design I; I. 12 VDC power supply input bus, 2. voltage
regulator array, one regulator to supply one color on five HEX arrays, 3. power resistor array, one for each color on 5 hex
arrays, 4. output fan, 5. output bus, 6. potentiometer bus. B) The Design I arrays in operation, tuned to an environment with-
out red (left) and without green (right) C) The components of the 36-element control unit; I. power supply, 2. 12 VDC bus,
3,4,5, red, blue and green circuit boards, 6. on-off switch/breaker, 7. pulse-wave modulator, 8. cooling fan. D) A diagrammatical
representation of the 36 HEX LED layout. The position of HEX arrays (green hexagons), wire pass-through holes (red circles),
ventilation holes (blue circles), and the vertical heat sinks (black bars) are presented. The complete 36-element array (top;
Panel E) and bottom (Panel F).



Page 5 of 11
(page number not for citation purposes)


BMC Plant Biology 2005, 5:17







http://www.biomedcentral.com/1471-2229/5/17


HEX HEX



R2 R2


Q Q



Rb Rb


To PWM


R1
AA-


HEX LED HEX LED HEX LED HEX LED HEN LED HEX LED HEX LED HEX LED HEX LED HEX LED HEX LED HEX LED HEX LED HEX LED HEX LED HEX LED
R 1 I RI f I tI RI RI RI R Ri R- Ri Ri RI RI

Rb Rb Rb Rb Rb R R Rb Rb Rb Rb Rb Rb Rb Rb Rb Red C it


HEX LEE HEX LED HE LE D HEX LED HEX LED LEE LE HE ED HE ED HE LED HEX LED HE LE HEX LED HE L HEX LED HE LE
R2 R2 R2 R2 R2 R R2 R2 R R R2 R2 R2 R2 R2

Rb Rb Rb Rb Rb ft ft Rb t R Rb Rb R Rb Rb % Geem C"uL


HEX LEE HEX LEG HEX LE HEX LED HE LE HEX LED HEX LE HEX LED HEX LED HEX LE HEX LE HEX LED HEX LED HEX LEC HEX LE HEX LEE


R2 fR2 R R2 b 2 Rb Rh R 2b Rb R Rb Rb R2 E t
s R




Figure 4
The circuitry powering the large LED banks. A) Two repeat units, driving two independent sets of 30 dies in Norlux HEX
arrays. Q = TIP 170 PnP transistor; RI = 22 ohm, I watt, metal film resistor (+/- 5%); R2 = 20 ohm, I watt, metal film resistor
(+/- 5%); Rb = 4.7 k ohm, Y2 watt, metal film resistor (+/- 5%). B) The assembly of the individual units into a controller for red,
blue and green circuits in a 16 HEX array.


Page 6 of 11
(page number not for citation purposes)


N I


BMC Plant Biology 2005, 5:17







http://www.biomedcentral.com/1471-2229/5/17


Blue light


D 0.5


5 50


B 14

E 12

-10

8

06

I 4

2

0


Fluence rate (pmol m-2 s-1)


D- 70
60
2 60
50
- 40
40
S 30
20
o in


-15 0 15 30 45 60
Time relative to pulse (min)


Red light


D 1 10 100
Fluence rate (pmol m-2 s-1)


0 0.5 1.5 2
Time of irradiation (h)


Figure 5
Norlux arrays induce typical light responses during early seedling development. A) Blue light fluence-rate response experi-
ments demonstrate the effect of increased fluence rates of blue light on stem growth after 72 h (filled circles; n = 60). The cryl
mutant was tested for comparison (n = 62). B) Fluence-rate/response experiments were performed using red light and demon-
strate growth inhibition in wild-type seedlings (filled circles; n = 70) compared to phyB mutants (open circles; n = 60). C) The
stem-stimulatory effect of a short single pulse of green light is shown (open circles) and compared to previously published
results ([17]; filled circles), and dark growth kinetics (dotted line). D) Phototropic curvature in response to blue light was
measured in etiolated seedlings (filled circles; n = 21) and compared to results from previous reports ([30]; open circles).
These findings demonstrate how the HEX arrays and the designs presented herein have utility in study of integration of light
information from multiple photosensory systems.


through the phytochrome and cryptochrome systems,
respectively [20,261. The results of two independent flu-
ence-rate/response experiments using over 60 seedlings
are shown in Figure 5A and 5B. Figure 5A shows the
height of seedlings grown for 72 h under constant blue
light and Figure 5B shows the effect of the same treatment
with red light. The cryl and phyB mutants are presented as
controls. The data show that constant blue or red light


inhibit seedling elongation in a manner roughly propor-
tional to fluence rate. Inhibition is detectable even at low
fluence rate (<100 [mol m-2 S-1), leading to a strong inhi-
bition of stem growth elongation. The results of these tri-
als mirror the previously published results [27,28],
suggesting that the LED arrays described herein act in a
manner similar to those used previously.


Page 7 of 11
(page number not for citation purposes)


14

E
EI12

10
C
.2 8
08


0
4
I

2

n


1.6


. 1.4


0
1.2


0 1.0


1 0.8


'


BMC Plant Biology 2005, 5:17








http://www.biomedcentral.com/1471-2229/5/17


Table I: The complete parts list for both array designs developed.


Design 2 I x 36 RGB Arrays


20 NorLux HEX LED 90 Die, RGB Array, Part Number N9100-0005
4 14" x 18" x 3/4" aluminum blocks
4 alloy heat sinks, approximately 5" x 3" base
2 12 VDC, 25 A Regulated Switching Power supply
6 3" (80 mm) 12 VDC fan
12 I K ohm potentiometer
12 LM3 17 voltage regulator with matching heat sink
12 SPST switch
4 5-input RJ I I coupler on single telephone cable
12 RJ II connector
I large plastic project box
2 terminal bus, I ea per power supply
2 I 10 VAC standard 24 h timer
12 1.0 pF capacitor
12 0.1 pIF capacitor
12 I Q power resistor
12 I K Q resistor
I blank circuit board
Telephone cable, 2-pair, 22 AWG
Misc. wire and cable, stainless steel nuts, bolts and screws.




While phytochromes and cryptochrome effects are salient
as stem growth inhibition after days of growth in constant
light, other rapid responses involve other light sensors
and can be measured on the order of minutes rather than
days. Contrary to the effects of red and blue, a short single
pulse of green light stimulates rapid elongation of the
hypocotyl in the dark-grown seedling [171. The response
persists in all photomorphogenic mutants, it occurs when
plants are grown in constant dim red light, and growth
promotion is the opposite of what occurs when seedlings
are irradiated with red or blue light. This evidence renders
it difficult to conveniently ascribe this response to any of
the known light sensors, and it is likely being mediated by
a separate green-sensitive transduction pathway. Figure
5C, shows the results of 20 independent seedlings treated
with green light from the Norlux HEX arrays, compared to
previously published data [171. Seedlings irradiated with
a short, single pulse of green light begin to grow rapidly
within 15 min, attaining 140% of their dark rate before
growth rate declines to dark levels after an hour. The
results are highly similar to published findings, again
indicating that Norlux HEX arrays are a suitable alterna-
tive to other LED or fluorescent light sources.

Phototropism is the rapid curvature of the hypocotyl
toward a unilateral light source. In Arabidopsis phototro-
pism is blue light induced and is mediated by the
phototropins, autophosphorylating serine-threonine
kinases associated with the plasma membrane [291. The
response is exquisitely sensitive to blue light. Here wild-
type seedlings were irradiated from the side while being
imaged in 5-minute intervals with an infra-red CCD cam-


36 NorLux HEX LED 90 Die RGB Array, Part Number N9100-0005
I- 20" x 20" x 1/8" sheet of aluminum
- 24" x 24" x 3/8" sheet of gray CPVC plastic
I- 48" x 48" x 1/4" sheet of clear polycarbonate plastic
I- 8" x 16" x 6" NEMA waterproof Fiberglas composite electrical box
I- 15 VDC, 22 A Regulated Switching Power Supply
I- 25 A I 10 VAC breaker
2 3" (80 mm) I 10 VAC fan
I -5" (120 mm) 15 VDC fan
36 22 Q, 2 W composite resistor
72 20 Q, I W composite resistor
108 TIP 107 NPN Regulated Transistor
108 4.7 K Q I W composite resistor
I Pulse Wave Modulator (manufactured by NorLux)
3 Blank prototype circuit board
Misc. Connectors, wire and cables, stainless steel nuts, bolts, and
screws.







era (as in [301). The degree of curvature was monitored
over two hours and compared to previous results (Figure
5D). The results indicate that the rapid response of pho-
totropism is very similar between the arrays designed in
this study and those produced commercially.

Conclusion
As the availability of new technologies increases, research
programs are challenged with the need to retool their
capabilities to exploit their potential. Since many of these
new technologies are electronic and/or computer related,
a certain degree of technical prowess is required to move
ideas from the drawing board to application. The develop-
ment costs of these technologies may be significant. This
report offers two clearly applicable models of LED light
source development that may be implemented in the
study of plant growth and output, helping to narrow the
long-term challenges of illumination to support plant
growth. These designs allow the fine control of specific
wavebands shown to influence plant growth and develop-
ment. Such designs represent the first step in defining
conditions that will optimize, or perhaps even control,
plant growth and development. The light sources used in
this report sustain normal plant early developmental
responses, suggesting that they are an appropriate substi-
tute for, or complement to, other plant illumination
solutions.

Methods
The NorLux HEX LEDs (Norlux Corp., Carol Stream, IL)
were chosen for these applications because of their com-
pact size and power input to output efficiency. The device



Page 8 of 11
(page number not for citation purposes)


Design I 4 x 5 RGB Arrays


BMC Plant Biology 2005, 5:17







http://www.biomedcentral.com/1471-2229/5/17


is a 90-die, densely-clustered set of LED chips, 30 red (628
nm), blue (470 nm) and green (530 nm) in one device.
The HEX platform implements chip-on-board technology
which allows high fluence rates to be generated from a
relatively small ~2 cm-diameter source. The solid-state
design is affixed to a ceramic and steel support to facilitate
efficient heat transfer to the mounting substrate. These
qualities make the Norlux HEX array useful in applica-
tions where high fluence rates need to be generated in
minimal space, such as a growth chamber or experimental
setting. Most importantly, the RGB components may be
independently controlled to finely adjust the quality and
quantity of irradiance. Two designs of array controller and
array construction are presented. The first is the design of
the compact 5-HEX arrays, modular and tunable RGB
banks at the University of Florida. These were designed for
small spaces and use in studies of stem growth and plant
development in the model system, Arabidopsis thaliana.
The second design details the construction of the larger
light banks of 36 HEX arrays built for studies at Kennedy
Space Center. Here, larger light banks are required to
assess the effects of light quantity and quality on the
growth of specific crop species likely to be grown in space.
Complete parts lists for both array designs are presented
in Table 1. All materials are common electronics compo-
nents and may be obtained through local (eg. Radio
Shack) or online vendors [31,32].

Design I The tunable RGB banks at the University of
Florida
Research activities by this research group at the University
of Florida center on developmental transitions, namely
the progression of seedling growth between dark and light
environments as well as the vegetative/floral transition.
These processes are all controlled by a well-defined set of
photosensors, responsive to the various portions of the
spectrum. The ability to independently control specific
wavebands makes it possible to assess how independent
light sensing systems integrate environmental informa-
tion to tailor the developmental response in question.
Experiments are performed on small seedlings or through-
out the life cycle of Arabidopsis thaliana plants, so an opti-
mal light bank would be self contained, relatively small,
and easily moveable. With these considerations in mind,
the tunable RGB banks were developed. Each tunable
RGB bank consists of 5 HEX arrays (Figure 1), 150 total
dies, where the red, blue and green dies are independently
adjustable. 20 HEX arrays allow for 4 independent light
banks that may be run simultaneously with equal spectral
output to irradiate a large area (~1.0 x 0.25 m). Alterna-
tively, each may be independently controlled to illumi-
nate up to four separate spectral quality/quantity
conditions at the one time. Two separate photoperiods
may be controlled using two independent power supplies
and timers.


Control unit
The Control Unit (CU) was designed to support twenty
HEX units, four sets of controls to regulate RGB
independently on five HEX units. By specification, the
Norlux HEX array has a maximum input voltage of 11.7 V
and 1.5 A of input current (200 mA per HEX). A circuit
was developed where a single potentiometer controls the
output from each of the red, blue and green LED arrays in
5 separate HEX units. A single circuit that controls one
color in five arrays is shown in Figure 2A. This circuit con-
sists of a standard 25 A power supply delivering 13.8 VDC
to a common bus that feeds an LM317 voltage regulator.
Voltage to the array is modulated by a potentiometer as
well as an in-line switch. A 1 K ohm power resistor is
placed in the circuit as a current limiter. The voltage
regulator and the LEDs require a stable DC input. Input
and output capacitors were added to minimize ripple for
improved transient response. A more stable voltage wave-
form assures consistent output. This simple configuration
is repeated for each color. There are twelve individual cir-
cuits in the control unit, each controlling R, G, or B in
each of four light arrays.

In Design 1, the LM317 voltage regulator is used to ensure
an output of 1.5 A, which is important to achieve the max-
imum light output, yet each generates substantial heat.
The voltage regulator has a threshold temperature of
125 C, and the twelve regulators used in this design must
be equipped with individual heat sinks. The CU was out-
fitted with two 80 mm 12 V fans, one facing into, and one
facing out of the CU. Each of the individual voltage regu-
lators was outfitted with an individual heat sink to assure
adequate cooling.

The RGB bank
Each Tunable RGB Bank consists of five RGB HEX arrays
affixed to a 12.5 mm solid aluminum support (Figure 2B
and 2C). To allow for modular removal, replacement or
service of individual HEX units, the four HEX array con-
nection wires (1 each, RGB anodes and ground) were
attached to a standard RJ 11 telephone connector. The out-
put of the CU terminates in a 5-input RJ11 coupler where
all five HEX arrays could be easily, yet reversibly
interfaced.

Thermal issues must be considered in construction of the
light source. The LEDs have a maximum temperature rat-
ing of 110 C. To maintain full operation without heat
damage to components, the NorLux HEX arrays required
mounting to a substrate capable of efficient heat transfer
and dissipation. In this design, HEX arrays were affixed to
solid 18 mm aluminum blocks with heat-sink compound
and metal screws (Figure 2B). A black-anodized alloy heat
sink was attached to the aluminum block and an 80 mm
fan was installed over each unit (Figure 2C). With this


Page 9 of 11
(page number not for citation purposes)


BMC Plant Biology 2005, 5:17







http://www.biomedcentral.com/1471-2229/5/17


configuration the aluminum block temperature did not
exceed 45 C. A low operating temperature not only
assures consistent LED output, but also is important as
radiant heat may perturb plant growth and/or
development.

The modular design of the four Tunable LED Banks per-
mits the capacity to control the quantity and quality of
actinic light in plant experiments (Figure 3A). In this
arrangement up to nine 2.5" (6.35 cm) pots containing
rosette plants such as Arabidopsis may be grown under a
fluence rate of 75 [tmoles m-2 s-1 (+/- 5 [tmoles m-2 S-1) at
15 cm vertically below from the light fixture (Figure 3B).
Alternatively, seedling hypocotyl growth experiments on
Petri dishes may be performed at much closer proximity
(5 to 7 cm) where a uniform fluence rate of over 100
moless m-2 s-1 is readily obtained.

Design 2 The large RGB light banks at Kennedy Space
Center
Unlike the small 5-array banks described previously, large
36 HEX LED light fixtures were developed to accommo-
date the uniform irradiation of large flats of plants used in
the study of crop production for advanced life support in
space. The fixtures were made from polycarbonate and
CPVC plastic sheets, aluminum and stainless steel. Like
the previous design, the large banks are comprised of
three separate units: a power supply/control unit, a timer,
and a light fixture.

Control unit, power requirements and capability
The physical layout of the 36-Norlux HEX array control
unit is shown in Figure 3C. Each LED component was
independently controlled by using a pulse wave modula-
tor (PMW; number 7 in Figure 3C) made by NorLux to
control the electronic circuits for each RGB component to
the desired irradiance. The controller consisted of a NEMA
electrical box housing the power supply, the circuit boards
and the PWM with control knobs for adjusting each cir-
cuit of HEX LED units. Each set of 30 R, G, or B dies in
each HEX array was powered by a single circuit consisting
of a TIP 107 PNP transistor, a 22 ohm, 1 watt resistor and
a 20 ohm, 1 watt resistor assembled as in Figure 4A. This
unit is repeated multiple times, one for each color on each
array (Figure 4B). For each color, all of these circuits are
placed in parallel and controlled by a single potentiome-
ter. An electronic timer was used to set the photoperiod
for the lights with the capability of 4 on/off programs for
the complete system. This timer was purchased locally
that could satisfy the voltage and ampere load require-
ment. The electrical power requirements were 110 volts
AC and 18.72 amps maximum for all the HEX LEDs.
When the HEX LEDs are operating at 100% power they are
using approximately 432 watts. The entire system uses
approximately 1980 watts at full operating power. At


25 C each RGB HEX LED requires 520 mA total, red 120
mA, green 200 mA, and blue 200 mA.

The RGB 36-array bank
The aluminum, CPVC, and polycarbonate sheets were
measured, cut, and assembled to create a light fixture to
mount the Norlux HEX LEDs and designed to fit into cus-
tom racks within the Advance Life Sciences growth cham-
bers at Kennedy Space Center. The custom light fixture
with attached aluminum plate has dimensions of 20" x
20" x 3" (50.8 cm x 50.8 cm x 7.62 cm). The HEX LEDs
were mounted directly to 0.125" (3.175 mm) aluminum
sheet 20" x 20" (50.8 cm x 50.8 cm) with thermal paste to
allow sufficient heat dissipation. The HEX LEDs were
evenly distributed on the aluminum sheet (Figures 3D
and 3E). Although the aluminum sheet was the primary
heat sink for cooling the HEX arrays, secondary aluminum
heat sinks were added in a vertical arrangement inside the
light fixture for added cooling (Figure 3F). Three cables
with 37 conductors (22 AWG) were connected from the
light fixture to the circuit boards, one cable for controlling
the red components (i.e., 1080 red dies) from 36 HEX
LEDs, one for the green components (i.e., 1080 green
dies) from 36 HEX LEDs, and one for the blue compo-
nents (i.e., 1080 blue dies) from 36 HEX LEDs. The light
output is approximately 150 [tmoles m-2 s-1 at the center
and approximately 85 [tmoles m-2 s-1 at the edges when
measured with a radiometer 30.5 cm vertically below
from the light fixture. Fluence rates decreased at the edges,
suggesting great care to be exercised in positioning of LED
arrays relative to the specific application.

Validation of LED HEX arrays using early
photomorphogenic responses
The end-point hypocotyl elongation assays were per-
formed by arranging seed in a line on a square Petri dish
placed vertically under the light source. Individual seeds
were placed on media containing 1 mM KC1 and 1 mM
CaCl2, they were stratified at 4C for 48 h and then were
placed into the respective conditions for 72 h. Seedlings
were imaged at high resolution and hypocotyl length was
measured from digital images using Image Tool (Win-
dows Version 3.0) software. Hypocotyl kinetics in
response to green light and phototropic curvature induced
by blue light were performed as previously described
[17,30].

Authors' contributions
KF designed and fabricated facets of the RGB HEX array
electronics and structural elements at the University of
Florida (UF), performed all physiological assays and
drafted the manuscript. LK designed and fabricated the
HEX array platform at Kennedy Space Center (KSC). RM
and JDK designed and assembled the circuit board in the
UF control unit and engaged in troubleshooting the


Page 10 of 11
(page number not for citation purposes)


BMC Plant Biology 2005, 5:17








http://www.biomedcentral.com/1471-2229/5/17


arrays. H-HK, RW and JS provided conceptual designs and
oversaw the practical implementation of the technology at
KSC.


Acknowledgements
The Norlux HEX arrays at the University of Florida were purchased with
funding from NASA grant NAG 10-316 (KMF). The control unit and student
technical support were funded by the University of Florida University
Scholars Program (RM), with additional support from the National
Research Council Resident Research Associate Program (H-HK). This
work was supported by the Florida Agricultural Experiment Station and
was approved for publication as Journal Series Number R-10919.

References
I. Shinkle JR, Atkins AK, Humphrey EE, Rodgers CW, Wheeler SL,
Barnes PW: Growth and morphological responses to different
UV wavebands in cucumber (Cucumis sativum) and other
dicotyledonous seedlings. Physiol Plant 2004, I 20:240-248.
2. Johnson CF, Brown CS, Wheeler RM, Sager JC, Chapman DK,
Deitzer GF: Infrared light-emitting diode radiation causes
gravitropic and morphological effects in dark-grown oat
seedlings. Photochem Photobiol 1996, 63:238-242.
3. Ahmad M, Grancher N, Heil M, Black RC, Giovani B, Galland P, Lar-
demer D: Action spectrum for cryptochrome-dependent
hypocotyl growth inhibition in Arabidopsis. Plant Physiol 2002,
129:774-785.
4. Knieb E, Salomon M, Rudiger W: Autophosphorylation, Electro-
phoretic Mobility and Immuno-reaction of Oat Phototropin
I under UV and Blue Light. Photochem Photobiol 2004.
5. Spalding EP, Folta KM: Illuminating topics in plant photobiology.
Plant, Cell and Environment 2005, 28:39-53.
6. Yadav V, Kundu S, Chattopadhyay D, Negi P, Wei N, Deng XW,
Chattopadhyay S: Light regulated modulation of Z-box con-
taining promoters by photoreceptors and downstream reg-
ulatory components, COPI and HY5, in Arabidopsis. Plant j
2002, 31:741-753.
7. Rousseaux MC, Ballare CL, Jordan ET, Vierstra RD: Directed over-
expression of PHYA locally suppresses stem elongation and
leaf senescence responses to far-red radiation. Plant Cell and
Environment 1997, 20:1551-1558.
8. Parks BM, Spalding EP: Sequential and coordinated action of
phytochromes A and B during Arabidopsis stem growth
revealed by kinetic analysis. Proc Natl Acad Sci U S A 1999,
96:14142-14146.
9. Kiss JZ, Mullen JL, Correll MJ, Hangarter RP: Phytochromes A and
B mediate red-light-induced positive phototropism in roots.
Plant Physiol 2003, 131:1411-1417.
10. Usami T, Mochizuki N, Kondo M, Nishimura M, Nagatani A: Crypto-
chromes and phytochromes synergistically regulate Arabi-
dopsis root greening under blue light. Plant Cell Physiol 2004,
45:1798-1808.
I I. Casal JJ, Sanchez RA, Deregibus VA: The Effect of Plant-Density
on Tillering the Involvement of R/Fr Ratio and the Propor-
tion of Radiation Intercepted Per Plant. Environ Exp Bot Environ
Exp Bot 1986, 26:365-371.
12. HeoJW, Lee CW, Murthy HN, Paek KY: Influence of light quality
and photoperiod on flowering of Cyclamen persicum Mill. cv.
'Dixie White'. Plant Growth Regulation 2003, 40:7-10.
13. Heo J, Lee C, Chakrabarty D, Paek K: Growth responses of mar-
igold and salvia bedding plants as affected by monochromic
or mixture radiation provided by a Light-Emitting Diode
(LED). Plant Growth Regulation 2002, 38:225-230.
14. Markelz NH, Costich DE, Brutnell TP: Photomorphogenic
responses in maize seedling development. Plant Physiol 2003,
133:1578-1591.
15. Kim HH, Goins GD, Wheeler RM, Sager JC: Green light supple-
mentation for enhanced lettuce growth under red and blue
light-emitting diodes. Hortscience 2004, 39:1617-1622.
16. Kim HH, Goins GD, Wheeler RM, Sager JC: Stomatal conduct-
ance of lettuce grown under or exposed to different light
quality. Annals of Botany 2004, 94:91-97.


17. Folta KM: Green light stimulates early stem elongation,
antagonizing light-mediated growth inhibition. Plant Physiol
2004, 135:1407-1416.
18. Kim HH, Wheeler R, Sager JC, NorkianeJ: Photosynthesis of Let-
tuce Exposed to Different Short Term Light Qualities. Envi-
ronmental Control in Biology 2005, 43:113-119.
19. Shinomura T, Nagatani A, Hanzawa H, Kubota M, Watanabe M,
Furuya M: Action spectra for phytochrome A- and B-specific
photoinduction of seed germination in Arabidopsis thaliana.
Proc Natl Acad Sci U S A 1996, 93:8129-8133.
20. Parks BM, Folta KM, Spalding EP: Photocontrol of stem growth.
Curr Opin Plant Biol 2001, 4:436-440.
21. Went FW: The Experimental Control of Plant Growth.
Waltham, MA, Chronica Botanica; 1957:343.
22. Klein RM, Edsall PC, Gentile AC: Effects of near ultraviolet and
green radiations on plant growth. Plant Physiol 1965, 40:903-906.
23. Valverde F, Mouradov A, Soppe W, Ravenscroft D, Samach A, Coup-
land G: Photoreceptor regulation of CONSTANS protein in
photoperiodic flowering. Science 2004, 303:1003-1006.
24. Briggs WR, Huala E: Blue-light photoreceptors in higher plants.
Annu Rev Cell Dev Biol 1999, 15:33-62.
25. Lin C: Blue Light Receptors and Signal Transduction. Plant Cell
2002, Supplement 2002:S207-S225.
26. Chen M, Chory J, Fankhauser C: Light signal transduction in
higher plants. Annu Rev Genet 2004, 38:87-117.
27. Huq E, Tepperman JM, Quail PH: GIGANTEA is a nuclear pro-
tein involved in phytochrome signaling in Arabidopsis. Proc
Natl Acad Sci U S A 2000, 97:9789-9794.
28. Lin C, Yang H, Guo H, Mockler T, Chen J, Cashmore AR: Enhance-
ment of blue-light sensitivity of Arabidopsis seedlings by a
blue light receptor cryptochrome 2. Proc Natl Acad Sci U S A
1998, 95:2686-2690.
29. Briggs WR, Christie JM: Phototropins I and 2: versatile plant
blue-light receptors. Trends Plant Sci 2002, 7:204-210.
30. Folta KM, Leig EJ, Durham T, Spalding EP: Primary inhibition of
hypocotyl growth and phototropism depend differently on
phototropin-mediated increases in cytoplasmic calcium
induced by blue light. Plant Physiol 2003.
31. Digikey Inc. www.digikey.com. .
32. Mouser Electronics www.mouser.com..


Page 11 of 11
(page number not for citation purposes)


Publish with BioMed Central and every
scientist can read your work free of charge
"BioMed Central will be the most significant development for
disseminating the results of biomedical research in our lifetime."
Sir Paul Nurse, Cancer Research UK
Your research papers will be:
available free of charge to the entire biomedical community
peer reviewed and published immediately upon acceptance
cited in PubMed and archived on PubMed Central
yours you keep the copyright

Submit your manuscript here: BioMedcentral
http://www.biomedcentral.com/info/publishing adv.asp


BMC Plant Biology 2005, 5:17




University of Florida Home Page
© 2004 - 2010 University of Florida George A. Smathers Libraries.
All rights reserved.

Acceptable Use, Copyright, and Disclaimer Statement
Last updated October 10, 2010 - - mvs