LED irradiation has proved to be effective for plant growth and development.
Yes, constant or pulsed irradiation has been studied as a means of increasing the efficiency of photosynthetic microorganisms such as cyanobacteria and microalgae. So keep constant is very important to obtain results of these studies. It depends on the photosynthetic apparatus of the microorganism, but usually can best efficiency of use of light.
Some articles:
http://www.aidic.it/cet/14/38/036.pdf
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0038975
http://link.springer.com/article/10.1007%2Fs00449-014-1125-5
yes, several reports are also available in cabbage, lettuce, mustard etc
you can refer the attaches article for information
If you mean LEDs of certain wave lenght, they certainly do influence plant growth. For example, red and far-red light interact with plant phytochromes and influence metabolism and development processes.
I fully agree with the statements given above by some colleagues.
Please keep in mind: Plants (like any materials) do ABSORBE PHOTONS. What counts are the wavelenghts (what color) of each photon and the intensity of the light beam in terms of how many photons absorbed by the plant per e.g. leaf area. LEDs are electronic photon emitters of different emission spectra (color and band with a certain amount of photons emitted per unit time and one LED). The plant absorbs only a fraction of the emitted photons from the LED derermined by the absorption spectrum (or 1 - Transmission spectrum) of the plant. Once a photon from a LED excited a pigment molecule, the plant does not distinguish the different light sources of the photons. For the reaction of the plant counts as well the "mode" of illumination, such as continuous light, pulsed light, light flashes etc. However for equal constellations of light color, light intensity and illumination mode, the plant does not care about the ORIGINE (instrument LED, sun, moon, or any lamp).
The only question is if the PHOTORECEPTOR (in plants or animals etc) got excited or not in a certain illumination mode. All the rest is bioenergetics of photobiological systems (e.g. vision, phytochrome regulation, photosynthetic light energy storage in food etc).
LEDs are often very great tools due to their small size, constant light emission, very low heat production, long life and low price and very fast on-off switching.
Good luck
The answer of Reto J Strasser is absolutely perfect. LED-s are just the type of light source. Everything else depends on the spectral composition of the emitted light and its intensity. If you want to examine the impact of spectral composition of light on the metabolic processes of plants you have to use special LED matrix. You can make them to design own.
Best regards
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