Light is a critical factor. Orchids vary in their light requirements. With insufficient light the foliage becomes very dark green, and new growth is weak and spindly. Different orchids naturally have differing degrees of “greenness”, so consider the genus when you evaluate this. Insufficient light also affects flowering, which may be reduced or eliminated entirely. The light in the prospective exposure needs to meet the minimum requirement for the chosen orchid.
With too much light foliage may become yellowish-green or red. Sunburn can result if light conditions are suddenly changed to a direct exposure. Sunburn produces scorched blotches on leaves or overall yellowing of the plant.
Artificial light poses entirely different considerations than natural light. Group orchid plants of similar height together and use full-spectrum fluorescent bulbs. Alternately use cool (blue light) and warm (red light) fluorescent bulbs in the same light fixture. Light the bulbs for 12—16 hours per day, no more, and place them about six inches above the plants.
Weak growth and no flowers will result if there is insufficient artificial light, or if the temperature is too high when the lights are on. If the lights are drying out the atmosphere too much the orchids will have weak, shriveled, stunted growth. And if plants have good growth but fail to flower, the lights are being left on too long for short photoperiod (short day) orchids.