Most house plants can be grown under fluorescent lamps alone, although it is a common practice to mix incandescent and fluorescent light in the ratio of two or three florescent lamp watts to one incandescent lamp watt. This provides the proper light quality without excessive heat. Daylight, warm white, and natural white tubes can also be combined in various ratios to provide a suitable quality for plant growth.
Gro-Lux, Plant-Gro and other brands of agricultural fluorescent lamps are specially designed to provide a balance of red and blue light suited for plant growth.
(The two most commonly used gases for horticultural lighting are mercury vapour, producing a green blue light with no red, and sodium, producing yellow light. Modified mercury lamps produce the desirable red light missing from the basic emission.)
Low-pressure mercury-filled full spectrum fluorescent tubes produce diffuse light and, when suitably grouped in banks, provide uniform light close to plants.
Probably the most useful lamp for supplementary lighting in a greenhouse is a high-pressure sodium lamp, which produces a high intensity of light, and is relatively efficient