An African violet requires light intensity of 10,760 to 16,140 lux (1,000 to 1,500 foot-candles). Young plants grow best at 8,600 lux (800 f-c). All plants will remain at the vegetative stage if the light available remains below 5,380 lux (500 f-c).
To better illustrate the significance of these figures, 5,380 lux represents the amount of natural light that falls on a cloudy winter day, while 10,760 lux represents the amount received in a well-lit room on a clear spring day.
Light intensity is not a fixed value in a particular setting, but rather changes with the seasons and exposure to the sun. It is best to grow plants on a sunny windowsill with a southern exposure during the winter, although east and west exposures are also suitable.
From March to September, however, it is better to choose an east-facing window. Otherwise, the stronger rays of the sun may damage the fleshy tissue of the leaves by destroying chlorophyll, and dry brown spots will appear on the leaves. Alternatively, the plant may be set back from the window, or curtains or blinds used to shade it somewhat from the bright light.
Finally, the plant should be turned one quarter turn at each watering or once or twice a week to preserve its symmetry.
Unfortunately, it is not always possible to offer African violets ideal growing and light conditions. Some amateur growers have only windows that receive little sun, causing the plant to become etiolated, characterized by excessively long leaf stems. In such conditions, the plant will not bloom. Artificial lighting is a simple solution to compensate for a lack of natural light. Plants grown under fluorescent tubes will remain symmetrical and bloom almost constantly. African violets require at least twelve hours of light daily in order to bloom.
The African violet is native to a tropical environment, where temperatures can climb to 30 to 32°C and never fall below 18°C.
This partly explains why it adapts so easily to household temperatures. Nonetheless, it is best to maintain a difference of approximately 5°C between daytime and nighttime temperatures. Lowering the temperature at night will improve the plant's appearance in a number of ways. First, the flowers will be about 25% larger. There will be more petals and their colours will be more intense. Moreover, the white borders on bicoloured flowers will be brighter.
Finally, since variegated cultivars require cooler temperatures, they should be placed lower down on plant stands.