Buying Guide

Garden with Grow Lights

How to Choose Grow Lights

First, decide what you’re going to grow, and where you’ll place your lights. Natural sunlight has the colors of the rainbow: blue, red, violet, and yellow. Plants need the full spectrum, but use primarily red and blue. While you can use ordinary fluorescents to supplement any daylight that comes in your windows, specialty lights can allow you to grow plants in dark spots that receive little or no light at all.

Traditional fluorescent lights, like those used in shop light fixtures, are the most economical. They’re a good choice if you only need to supplement natural light. These bulbs come in cool, warm, or full-spectrum.

Full-spectrum fluorescents are recommended for seedlings, because they don’t give off a lot of heat that could damage tender foliage. Position them about 2-4″ above the seedlings, and raise them as the plants get taller. They’re also a good choice if your fixtures will be in or around living areas, because full-spectrum light is similar to natural light and won’t distort colors of your plants.

High intensity discharge lights (HDI) are the brightest grow lights and about twice as efficient as fluorescents. They must be used in special fixtures with ballasts.

There are two kinds of HDI lights: metal halide, or MH, and high-pressure sodium, also known as HPS.

MH lights are most intense on the blue end of the spectrum and promote foliage/vegetation growth. Because the lamps don’t distort colors, they can be used in living areas, like full-spectrum fluorescents. Use them to start your seedlings, and change to HPS lights when you want to promote flowering.

HPS bulbs are stronger at the red/orange end of the spectrum, so they’re better for flowering plants. It’s a good idea to combine them with MH lightning or with natural daylight, so your plants won’t become long and leggy. Use these bulbs away from living areas, since their illumination distorts colors.

Note: MH bulbs and HPS bulbs need different kinds of fixtures. If you want both types of light, you’ll need multiple fixtures or a special conversion bulb that allows you to change bulbs without changing ballasts. Always use caution when setting up any kind of lighting or wiring system to avoid injury or property damage.

Make a Space for Grow Lights

If you’re short on space, you can make a grow light stand with multiple shelves. Use casters on the bottom, and your stand can be rolled away into storage when it’s not in use. Or, if you’ve used it to start your seeds, you can replace them with houseplants that need extra light when you move your seedlings into the garden.

Tips for Using Grow Lights
  • If you use grow lights in an enclosed space, make sure you have adequate air circulation, so they don’t generate enough heat to harm your plants or fixtures.
  • Rotate your plants weekly. The light is more intense in the center of the bulbs than at the ends, so this will help them grow more evenly.
  • When the lights are off, occasionally wipe them with a clean, dry cloth. Built-up dust and dirt can reduce the amount of light they provide.
  • Watch the end of the grow bulbs, and replace the bulbs when they become dark. That’s a sign that the bulbs are getting old.
  • To be sure your plants aren’t getting too hot under the grow lights, briefly put your hand near the foliage. If it feels too warm, raise the bulbs higher (or lower the shelves if you’re using an adjustable grow light stand).
  • Use a timer to control the lights. Constant light can inhibit growth and the setting of buds and fruit.