Light is measured in a standard unit called a foot-candle (fc). A foot-candle is the equivalent amount of light that is produced by an international candle at the distance of one foot.

A lumen is the term used to measure the intensity of the light. It is the total amount of light energy given off by a light source. (As you move your plant away from the light source, the lumens striking the leaf surface will correspondingly decrease with more distance.) Foot-candles (fc) ÷ 10.76 = Lumens (lux).

The Light Meter is commonly used to measure how much light a particular plant is currently receiving. It measures in foot-candles, and it usually comes with a light chart specifying the light requirements of a wide variety of common plants.

INDOOR LIGHT DURATION AND INTENSITY

Duration: A general rule of thumb is that 12-16 hours of natural or artificial light, or a combination of the two, are needed to promote active growth. Not enough hours of light will slow or stop plant growth.

Intensity: Intensity varies enormously from plant to plant.