Ultraviolet Radiation – Artificial Light Sources
Ultraviolet (UV) radiation has long been known to be quite important in biological photochemical reactions. Anthocyanin and other flavinoid pigments absorb blue and UV light to protect chlorophyll from photo-destruction. UV-A, or near UV, is comprised of energy between 315 nm and 400 nm and has been found to support various plant functions as well as help to control various mildews. Lower wavelengths of UV (UV-B and UV-C) have been shown to be harmful to plants, damaging DNA, proteins, lipids and membranes.
Approximately 3 to 5 percent of the sunlight hitting earth’s surface ultaviolet light (below 400nm). Ninety-five percent of this ultraviolet energy is UV-A and 5 percent is UV-B.
In comparison, artificial light sources typically produce the following percent of UV-A compared visible spectrum:
Ceramic Metal Halide (CMH) lamps: 1.5% or less
High Pressure Sodium (HPS) lamps: 1.5% or less
Double-ended HPS lamps: 1.0% or less
Leading brand LED fixture: 1.0% or less
For HID lamps, harmful UV is typically cut off by the outer jacket (glass) or specially ‘doped’ quartz due to the medical hazards associated with high amounts of UV. Since UV output from artifical light sources is governed by the FDA, light bulbs are typically engineered to greatly exceed the FDA requirements, thereby producing very low levels of UV.