Most vegetables and garden plants require at least 16 to 18 hours of light each day; without enough light, they get pale and leggy. The conventional advice was to turn lights on for 16 hours each day. However, some growers maintain that 24 hours of consistent light every day provides a better outcome when growing seedling (i.e., there’s no need to give seedlings a nightly rest but this advice doesn’t necessarily apply to full-grown plants).
These types of bulbs produce two to three times more light than incandescent bulbs for the same amount of energy and are the most inexpensive lights for indoor gardening. However, they usually require bulky external ballasts (like, for example, overhead shop lights) so aren’t as easy to work with as incandescent and LED bulbs.
Different plants have different light intensity needs, but most seedlings grown for the garden will need higher intensity light to flourish. In general, the leaves should be about 2 – 4 inches away from the light source (assuming use of a fluorescent bulb – see below).
Unlike other bulbs which produce light across a broad spectrum, light-emitting diodes (LEDs) give off light within a narrow band. LEDs designed for growing plants emit light in the two bands that plants need – red and blue. The result is a purple glow that not everyone likes.
This primer on indoor lighting for seed starting will help you choose the options that work best for you.
These include halogen bulbs and are the type of light bulbs still used in most homes (although they’re getting harder to find now that stores are carrying only more efficient bulbs, such as CFLs and LEDs).
You can choose between incandescent, fluorescent, LED, and high-intensity discharge (HID) bulbs, each of which has its own pros and cons. Choose the grow light that works best for the type of plants you want to grow and where you plan to grow your seeds.
Incandescent bulbs, and especially halogen bulbs, also produce a lot of heat in relation to the amount of light they give off; plants growing too close to the bulb can be easily burned.
Full-spectrum fluorescent bulbs produce a balance of cool and warm light that replicates the natural solar spectrum, although these are less energy efficient than other fluorescent bulbs and tend to produce more heat. But, given the wider range of light frequencies emitted by these bulbs, they are a good choice for growing seedlings.
A description and comparison of different grow lights for starting seeds and growing plants indoors. Covers incandescent, fluorescent, LED and high intensity discharge lamps, as well as issues around light color, intensity and duration.