Fluorescent grow lights are a very convenient way to provide your plants with light. They’re readily available and the most popular choice among home gardeners and easier to set up than high-intensity discharge lights.
Fluorescent lights provide a more sun-like spectrum of light than ordinary incandescent bulbs. This makes them usable as grow lights.
How Plants Use Light
Plants use different parts of the light spectrum for different stages of growth. The initial growth stage requires blue light while the later flowering stage also needs orange to red light. Plants don’t use green light. Bear this in mind when buying fluorescent bulbs.
Keeping the light source close to the plants is important. And because fluorescent bulbs don’t generate much heat, it’s possible to do so. If you double the distance between the light source and the plant, the plant only gets a quarter of the light. Keep the light bulbs 2.5 to 10cm (1 to 4 inches) from the tops of the plants.
How much light do you need? A good rule of thumb is 25 Watt per square foot if the grow lights are the only light source.
It’s always a good decision to make use of a fan when you use grow lights to make sure the area doesn’t get too hot.
Fluorescent tubes emit light in 360 degrees, but are placed above the plants they’re lighting. So it makes sense to use a reflector to direct the light fully towards the plants to make the best use of the available light.
Fluorescent lights need an electrical circuit called a ballast to control the current flow to the bulb. Ballasts are the little “starter” devices you’re familiar with on fluorescent strip lights.
What is the Best Fluorescent Bulb for Indoor Gardening?
If your plants are in the initial growth (vegetative) stage, look for a bulb that is labelled “cool” or “cool white”. These bulbs emit more blue light which is needed in this growth stage.
During the flowering stage look at adding a “warm white” tube to your setup to provide the orange/red light that your plants need.
Fluorescent Light Bulb Sizes
There’s a standard naming convention for fluorescent lamps. The tube diameter is designated by a number after the letter T. In countries using the imperial system, the diameter is in eights of an inch. In the metric system, the diameter is given in millimeters.
So a T5 fluorescent lamp is 5/8″ in diameter and in metric would be a T16 lamp. It is the most commonly used fluorescent light size in indoor gardening.
A T5 comes in different lengths to suite different requirements.
Compact Fluorescent Lights
Compact fluorescent lights (CFLs) are what we commonly call “energy saving lightbulbs”. And they are now available as grow lights and just as efficient as the tube variety.
Ordinary home compact fluorescents generally not strong enough. Purpose-built grow light CFLs are mostly in the 90-200 Watt range.
Fluorescent grow lights are not the only choice for garden lighting. Other popular options are:
- High intensity discharge (HID) lights, including high pressure sodium and metal halide
- LED grow lights