All plant functions, from germination to photosynthesis to blooming, can be accomplished under light in wavelengths ranging from 300 to 700 manometers, or billionths of a meter.
Therefore, indoor gardeners need either incandescent “grow lights” or a combination of “cool” and “warm” fluorescent bulbs that give off light in that range.
Regular incandescent lights give lots of light at the long, red end of the spectrum, and plants grown under them tend to grow tall and gangly.
Under short wavelengths of blue-green light plants tend to produce a short growth of a weird dark color.
As to the ultraviolet light given off by bulbs, the amount is very low, less than sunshine in some bulbs, and does not harm plants.
