LED Light Sources for Plant Research -- UNDER CONSTRUCTION

a guide of commercially-available sources and how to build them yourself

Kevin M. Folta, Assistant Professor, Plant Cellular and Molecular Biology Program, Horticultural Sciences Department, University of Florida, Gainesville FL 32611.  kfolta@ifas.ufl.edu              Home Page

(If you came here from a search engine looking for "LED Zeppelin/Robert Plant" go back now)

Studies of photomorphogenesis (light-mediated development) in plants have benefited from the use of monochromatic light to isolate the effects of specific photoreceptors and the responses they mediate. For instance, blue light strongly inhibits hypocotyl (stem) elongation. This information has been used to screen mutant populations to identify individual plant lines that contain lesions in the light sensing apparatus. Growth of mutagenized seedlings under continuous blue light produced a series of plants with long hypocotyls (Koornneef et al., 1980). These were later shown to be defects in cryptochrome 1, a blue light sensor that directs stem growth inhibition (Ahmad and Cashmore, 1993).

Recent advances in semiconductor technology have produced light-emitting diodes (LED's) that produce high fluence-rate light at specific wavelengths. These are optimal for use in studies of photomorphogenesis in plants because:

• Their output can be controlled with simple electronics
• Their emission spectra are precise with narrow bandwidths
• They have low energy requirements
• They generate almost no heat

For these and other reasons LED technology is superior to colored filters used in conjunction with standard bulbs. We have used the following LED sources in photomorphogenic research and provide here a synopsis of the advantages and disadvantages of each commercially-available type. A description of how to build LED arrays follows.

Quantum Devices Q-Beam -- The old standby for photomorphogenesis research. Quantum Devices has supplied the phytochrome research with an outstanding tool: the red/far-red light source. The Q-Beam has output in both red and far-red that are both controllable in a very linear manner. A timer controls light pulses to 0.1 s. Red to far-red ratios can be established. These are also available in blue.  Advantages:  Precise fluence-rate control, internally cooled, historical precedent.  Disadvantages: Bulky source and separate controller/power supply. Price: $3300 (you pay for precision).  Website: www.quantumdev.com

Norlux Hex Arrays -- Norlux produces a single chip-based array that contains red, blue and green LED's. They are sold as "demo" units with an RGB hex chip and an R hex-chip, or as single hex-chips. Advantages: Precise control of RGB. Quite linear control and excellent fluence rate. Small profile and excellent light propagation free of "hotspots".  Disadvantages: Red LED's emit at 630 nm. Far-red, UV etc may be available on request for an extra charge. Excellent product support and rapid shipping.  Price: "demo" units are around $250, single RGB chips are around $100.  Website:Their website is www.norluxcorp.com.

LEDtronics Floodlamps -- LEDtronics makes a variety of LED lamps for residential and commercial use. Typical applications include traffic lights, spot lights and automobile lamps. We have successfully used the blue and green 130-LED array. Advantages: Plugs into standard Edison base, high fluence rate output, 100,000 h lifespan, durable design. Disadvantages: Light-scattering plastic should be used to minimize "hotspots" LED's emit at 630 nm, no 730 nm available. Customer service seemed bothered by my inquiries. Price: $200-400 depending on wavelength. Website: www.ledtronics.com

Do it Yourself!  COMING SOON!  Please contact us if you would like this information sooner!

"One of the major problems with which both teachers and researchers is confronted is that of gadgetry."
    R.M. Klein (1963) American Biology Teacher 25: 96-100.

With $30 and a good roll of solder you can build your own arrays.  Simple electronics make them somewhat tunable, allowing precise combinations of UV, red, blue, green and far-red light. The picture above demonstrates the range and combinations we have created in lab from red, blue and green LED's, along with their spectral output as measured on a spectroradiometer. 

Basic Design -- ON/OFF, no fluence rate control.

The concept is simple. Two LEDs in series require 6V to light them.  A standard 6V power supply will run hundreds of LEDs as they have negligible current draw. The basic plan is to place two LED's in series, then place the sets of two in parallel. I have also used laptop power supplies as they have a 5V and a 12V DC output. The 5V drives sets of two LED's in parallel and the 12V can be used to drive a computer fan to assure even heat dissipation (optional).

Advanced Design --

The advanced design incorporates a solid-state power supply, a potentiometer, a single resistor and the LED lamps to generate a controllable output. Sets of red, blue, and green can be tuned to generate any color combination as in the photo above.

Coincidentally, a "yellow tip" pipette tip tray provides the perfect matrix to support 5 mm LED's.  Single LED's may be simply set into the holes or can be glued in with epoxy.