Measuring Light
Light is measured in foot-candles. One foot-candle is “the illumination at all points that are 1 foot from a uniform source of 1 candle-power of light.” If you use, or used to use a good 35 mm camera, you will be familiar with the term.

The intensity of light varies with the seasons. In summer, it may reach 10,000 foot-candles or more during the brightest part of the day. This is too much light for African violets, begonias, and decorative green pot plants. During winter months, light intensity may be reduced to a meager 500 foot-candles. Clouds and smoke from factories also reduce light.
When light intensity becomes too low, plant growth slows almost to a halt, stems become weak, leaves thin, and flowers are paler than under normal conditions. Under too-high light intensity, plants tend to wilt, wither, and may become yellowed or show burned spots.
With optimum conditions such as good soil, correct watering, and proper temperatures, food production in plants is stepped up as they receive more light. To achieve maximum growth and flowering, you must regulate light intensity to make up for sea¬sonal changes.

Shade your greenhouse during summer to cut down the light; remove shade to admit more winter sun; brighten all dark corners with artificial light.

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