CFL Light Requirements for Tomatoes
By Linda Richard
, last updated March 13, 2012
African violets and similar houseplants grow in low lighting conditions, but vegetables such as beans and tomatoes require more light. Incandescent reading lights provide a red light not conducive to plant growth. Compact fluorescent lights or compact fluorescent grow lights promote growth in plants. Grow lights and CFL lights provide ultraviolet light emission in a length that encourages plant growth. Tomatoes and large vegetable plants require this kind of lighting to thrive.
Watts, lumens or footcandles are measurements of lighting. A watt is the electrical consumption or energy required to burn the bulb or create the lighting, but does not measure the light produced. A lumen is a footcandle falling on one square foot of area. The output of the light is expressed in lumens, but the needs of the plants are calculated in footcandles. A footcandle is the light provided by one candle in a square foot area one foot away from the object. Lighting requirements for growing tomatoes is a footcandle calculation, measured at the plant.
Tomatoes and vegetables with high lighting requirements need 500 to 1,000 footcandles of light for normal growth. A sunny day provides as much as 12,000 footcandles outside and you may get as much as 1,000 footcandles indoors close to a southern-exposure window. A distance away from the window decreases the footcandles of light so that plants with low light requirements are the only indoor survivors. The size of the plant also affects the lighting requirements.
Compact Fluorescent Lights
Compact fluorescent lights provide cool but powerful lighting for vegetable plants with high lighting requirements. Tomatoes, cucumbers and beans need more light than herbs and lettuce. As these large plants grow, they require light distribution to all sides. CFLs and reflectors may create the ideal lighting for tomato plants. Because CFLs give off little heat, you can position them close to the plants without burning the tender leaves or flowers. A 125-watt CFL designed for plants may provide 8,500 lumens of lighting. Placing this light a foot away from the tomato plant will provide about 8,500 footcandles of lighting within the one-foot area of the light. The footcandles of light available are cut in half for every additional foot, so a 3-foot tomato plant may get sufficient lighting from one 125-watt CFL, but it will grow better with several CFLs distributed around the plant.
Variables and Alternatives
You can start tomato seedlings indoors in low lighting. As the plants grow larger, they need more footcandles of light. The tomato plant’s density and size determines the footcandles of lighting needed at any time. The plants need even distribution of lighting all around the plant, not just lighting from the top. You may see other lighting available for plants, including T-5 bulbs and high-intensity discharge lights. T-5 bulbs are not CFLs, but are more energy efficient. These bulbs are slimmer, but long like a standard fluorescent bulb. You won’t be able to get as close to the plant with this lighting. HID lights are either metal halide or high-pressure sodium high-intensity discharge lighting. Metal halide lights provide blue-spectrum light that encourages plant growth. High-pressure sodium lighting has an orange glow that encourages foliage growth. Sodium lighting works well in combination with sunlight to grow flowers and vegetables.