Effects of red/blue grow lights on roots

[cantrell]

Hi, all. I grow most of my orchids under red and blue LED grow lights, and I’ve noticed something interesting. Roots that are fully shaded from the light have very long, perfectly green tips whereas roots that grow exposed to the red and blue lights have shorter tips and are very red on top.

You can see a good example in the attached photo. The root at the top is shaded by the leaf above it, and the root in the foreground is fully exposed to the red/blue light (turned off for the photo). You can even see how the red root is green on the bottom where it isn’t exposed to the grow light. I’ve also seen green roots that start out shaded turn red and appear less healthy once they’re grown into the light.

So...

• Should I use full-spectrum, white lights instead? The plants are thriving, but roots protected from the red/blue LEDs appear healthier.
• Is the light simply too intense? I added a diffuser beneath the lights, but it will take some time to know whether it is making any difference.

My theory is that the light is simply too intense. The illumination is perfect as measured with a lux meter (about 1,500 foot-candles), but since the light only contains reds and blues, I wonder if that’s actually too much. In other words, I wonder if the illumination should be something like two-thirds the recommended illumination (maybe 1,000 foot-candles) since there’s no green, and no light outside the visible portion of the spectrum.

Anyone have any insight into what’s going on?

Thanks,
Christian