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

[MrHappyRotter]

Light spectrum can play a role in the color and growth pattern of plant tissues. However, in this case, I believe the difference in the roots is due to light intensity.

[cantrell]

Originally Posted by MrHappyRotter

Light spectrum can play a role in the color and growth pattern of plant tissues. However, in this case, I believe the difference in the roots is due to light intensity.

I think you may be right. The roots that are shaded from the light are as healthy as you could possibly want, and the roots directly exposed are the ones affected. I installed egg crate as a light diffuser, so I'll see if that makes a difference.

Thanks.

[nicola]

Hi,
I also use LED lights for my orchids. My lights are of the common type, a combination of warm and cool white.
Even with these LEDs when the light is too intense the tips of the exposed roots become reddish.
To remedy I increase the distance from the lamps.
I also believe that measuring the intensity of the blue and red light LEDs with a common lux meter is not reliable, it is probably much greater.
It is better to observe the color of the leaves and roots to make adjustments.
Happy growing new year
ciao Nicola

[cantrell]

Originally Posted by nicola

Hi,
I also believe that measuring the intensity of the blue and red light LEDs with a common lux meter is not reliable, it is probably much greater.

Agreed. I'll either switch to white lights, or do some trial and error.

I grow my Dracula orchids under white LEDs, and the lux meter seems to help me give them exactly what they need, but with red/blue grow lights, I think I'm way off.

Thanks,
Christian

[estación seca]

Red/purple roots are not a problem in and of themselves.