Light Spectrums' Effects on Plants

There has been a lot of research that identifies which plants need what sort of light (wavelengths) and intensity to germinate, grow, and flower. Generally speaking, plants utilize two sorts of light and for discussion I will call them "red" and "blue." The wavelengths between the red and blue peaks of the spectrum are more what our eyes see. This "visible" wavelength is something like 430-660 nanometers. At the extremes are UV and infrared, and neither of these is beneficial to plants. An overabundance can cause plant mutation and even death. UV is less than 400 nm and infrared greater than 700 nm. Excess UV mutates cells. Excess infrared burns plants. (For orchid growers and many other tropical plant growers, this infrared is what "sunburns" our plant's leaves.)

The so-called "visible" light, the range that our eyes can actually see, is not really beneficial to plant growth/bloom. That means that the vast majority of incandescent lighting won't help you much.

Most plants need a good measure of both red and blue spectrums. The useful blue is 400-450 nm and the useful red is 650-700 nm. These numbers become important IF you want to use some sort of Gro-Light.

For spring and summer bloomers, during the fall our light will move gradually from the red spectum to the blue spectrum. I'm talking about the Northern Hemisphere. As the sun gets lower in our southern sky, the blue spectrum increases. The blue triggers the plants to "change gears" from growing (vegetative) to blooming (budding). For fall/winter bloomers, just the opposite occurs. During the spring/summer, as the sun moves more overhead, there is more of the red spectrum and this triggers the plants to bloom in the fall/winter.