Introduction to indoor plant lights
Artificial lighting is widely used to supplement or replace natural light for indoor crops. Many plants grown indoors do well under artificial lights such as fluorescent. Plants do especially well when grown under High Pressure Sodium or Metal Halide lamps. Incandescent lights are not recommended for growing crops, as plants placed under them tend to stretch or become leggy. Grower's can possibly make up for insufficient light by increasing the time or duration that the plant is exposed to light. Sixteen hours of light and eight hours of darkness are satisfactory for most plants. Lights should be regulated with a UL listed, industrial strength timer, especially in applications using a lot of wattages.
Plants use light as a source of energy to manufacture food. The more light a plant receives the more energy it receives. Light is commonly measured in foot-candles (ft-c). Most rooms in an average sized home is often illuminated by less than 100 ft-c, while the outdoors on a clear, sunny day can exceed 10,000 ft-c. Different plant spiciest lighting requirements varies widely. Some plants prefer a lot of light while others don't. Indoor plants are often classified by the amount of light necessary for normal growth and follows as: low, medium, and very high light requirements.
The minimum amount of light plants need to sustain it self for one year is approximately 100 ft-c for 12 hours daily. At least 200 ft-c for 12 hours is required for foliage plants to utilize any benefits from fertilizers.
Requirements Minimum ft-c Preferred ft-c
Low 100 75-200
Medium 100-150 200-500
High 150-1000 500-1000
Very high 1000 1000+
This article courtesy of www.hydroponicsearch.com