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Spectral Shifting with LEDs

(An abridged version is found in the July 2011 issue of Maximum Yield.)

Light Movers Give Growers the Flexibility to Truly Customize Spectrums

By Brian Chiang and Josh Puckett

There seems to be no end to the advancements that LEDs are making. From each generation to the next, LEDs are clearly on the road to becoming the preferred lighting method in most applications, including the indoor growing industry! We've talked a great deal on the various advantages in using LED lighting in the horticulture industry, including energy savings, high quality, intense light, modular design, and spectrum tuning.

It's important to note that these last two points go hand in hand. The flexibility of LEDs comes from their small size and their ability to specify a wavelength per chip. For example, with individual blue and red LED chips, we can produce a purple LED light that you may be familiar with. This spectrum is actually a blending of specific wavelengths, made possible by dense matrix LED technology. Panel arrays with more sparsely populated colored LEDs more obviously demonstrate the same effect, though with less intensity. With LED panels, it is evident that what the plants are receiving is a combination of many different wavelengths of light. On the other hand, dense matrix LED technology compacts many LED chips into a small unit that has a much higher intensity.

Customizing Spectrums Using Light Movers

We've discussed previously how LEDs allow the grower to tailor a spectrum to the plant. There have been countless experiments detailing the different effects of various spectrums. Certain blue spectrums are known to strengthen vegetative growth, and parts of the red spectrum promote flowering and fruiting. Growers can use a combination of these spectrums to achieve the results that they want in their plants.

With the help of light movers, this concept of spectral shifting, or light blending can be achieved on a larger scale using dense matrix LED technology. Just as with individual LEDs, lights of different spectra can be targeted to plants consecutively to provide an altered overall spectrum. However, this is only possible if the grower can get all the necessary wavelengths to their crop. To do that, a light mover is essential.

An ideal light mover rotates around the grow area to transfer light to every inch of the plants. What's more, a light mover allows the grower to truly specify the spectrum they want their plants to receive. For example we could pass a 50-chip array of all blue diodes, followed by a 50-chip array of all red diodes and achieve similar results to a statically suspended 100-chip array of half red and half blue diodes above the plant. Traditional LED panels are too large for this to be implemented, so it is crucial that compact dense matrix LED lights are used, small enough to be installed onto light movers.

Comparing Static & Moving Light Treatments

To test this concept, we evaluated whether Husky Cherry Tomato growth beneath rotating light differed from those under statically suspended lights. For this experiment we compared two 4' x 4' growing areas, each containing six 36-watt LED purple units which ran for a period of 18 hours per day.

Within the first grow tents we suspended six static units, and in the other we slowly moved the units around using a prototype "light spinner". Results showed little, if any, difference in the growth habits of plants. This test was run multiple times, both for vegetative and reproductive growth, and the results were the same as the initial test.

Combining Different Light Intensities

The next experiment we designed to show the effectiveness of spectral shifting was to test whether rotating LED units of different wattage and spectral output would produce uniform results in plant growth. Experiments were conducted within a 4' x 4' grow tent with four test treatments, each consisting of four 90-watt magenta LED lights and two 36-watt LED lights of various spectra. Within each grow tent were four Beef Steak tomatoes planted in 4-gallon containers. The lights were run at a 12-12 photoperiod for duration of ten weeks.

Test Treatments
- 4 x 90W Magenta & 2 x 36W Magenta
- 4 x 90W Magenta, 1 x 36W Magenta, & 1 x 36W 3500K White
- 4 x 90W Magenta & 2 x 36W Purple
- 4 x 90W Magenta & 2 x 36W Blue

Though we observed different growth patterns per treatment, these patterns were uniform throughout each specific treatment. Where the light treatment caused internode elongation and petiole elongation, these effects were seen throughout each plant. Similarly, where the light treatment caused increased flower production and fruit set, each plant saw the same effects throughout the grow room.

Conclusion

From these results, we have developed methods of analyzing spectral influence upon plant growth. Using combinations of spectrally customized units and light movers we are easily able to shift the spectrum as well as intensity within a light treatment and evaluate its effect upon plants' growth. Using dense matrix LED technology in conjunction with a light mover, the indoor grower also now has the flexibility to customize their light environment and optimally meet the needs of their crops.

These tests demonstrate how the grower can design the light environment of their grow room with combinations of Dense Matrix LED units, just as engineers customize the spectral output of individual units with different diode configurations. Additionally the grower can add or remove units at desired intervals of the growth cycle to manipulate plant growth.

As we learn more about spectrum and its effect on plants, the versatility of LEDs to specify wavelengths continues to be relevant, and even necessary. Without this ability, we wouldn't be able to test and experiment with different spectrums. LED technology will continue to break boundaries and push the limits of lighting. The indoor growing industry can only benefit from the advancements that are made. Keep your eyes on this growing industry as we move forward togetherâ€"more exciting progress is sure to come!