How Many Inches Should a Grow Light Be From Vegetable Plants?
Grow light height above plants should be close enough for the vegetables to absorb the light they need but not so close that the lights burn the stems and leaves. You can use one of several types of grow lights to start and grow your vegetables, so consider what will work best for your indoor setup. Make sure you can move your lights as your plants grow taller.
Grow lights should be placed 3 to 24 inches away from your vegetable plants, depending on the type of lightbulb you select.
Types of Grow Lights
The type of grow light you select will not only determine how far you need to place it from your plants, but also other factors, including the amount of money you need to invest. Fluorescent bulbs are one of the cheaper options to purchase, notes the University of Minnesota Extension. However, they do not last as long as other types of bulbs and are less energy efficient, which means using them may have a bigger impact on your energy bill.
LED, or light-emitting diode, lights are another option with plenty of advantages. They produce little heat, which reduces the risk of burning your plants. They also use energy efficiently and last a long time. However, they are more expensive to purchase up front, and they emit a bright light, which may be distracting, depending on where you're growing your plants.
There are two types of high-intensity discharge, or HID, lights: metal halide bulbs and high-pressure sodium, or HSP, bulbs. They can provide a high level of light over a large area but emit a lot of heat, so you will need a system to cool them, which can lead to a costly energy bill, notes the University of Florida IFAS Extension. The bulbs are more expensive than most bulbs, and they need a more complex and expensive system to set up. This makes them unsuitable for most home gardeners who are attempting to grow vegetables inside.
Grow Light Height Above Plants
Placing the lights the correct distance away from your plants lets them absorb the light they need without burning the plants. The ideal fluorescent T5 grow light distance from plants is 3 to 12 inches, advises the Old Farmer's Almanac. LED grow light height above plants should be 12 to 24 inches above your plants and HID lights should be placed 24 to 60 inches above the top of your plant.
When you build or purchase a stand and light growing fixture, consider how tall your plants are likely to get. If you are starting vegetable seedlings to transfer to your garden later, then you may not need a fixture that allows you to adjust the lighting. However, if you are growing vegetables completely indoors, you will want to be able to adjust the height of the light as the plant grows. Also, consider whether you will need a fan for cooling if the bulbs you select emit heat.
In addition, make sure that you get enough lights so that every plant receives adequate light coverage. Fluorescent lights, for example, emit the most light from the center of the tube, which means that plants placed under the end of the light may not get what they need to grow, notes the University of Missouri Extension.
Plant Light Requirements
It's a good idea to set up your lights on a timer, so you don't have to remember to turn them on or off. Lighting your plants for the correct number of hours not only gives them the light wavelengths they need to grow, but it also signals the plants as to which season it is based on the number of hours of light they're receiving. The best time to run grow lights is during the day for up to 18 hours. Make sure your plants get at least six hours of darkness each day, advises the Old Farmer's Almanac.
The University of Minnesota Extension recommends 16 to 18 hours of light for seedlings and 12 to 14 hours of light for lettuce and herbs. You can also take into account the amount of light, if any, plants will receive from direct sunlight from the windows. While you can grow more complex plants like tomatoes indoors, many of them have high light requirements, so it's usually best to transplant them outdoors. If you opt to grow them inside exclusively, select high-intensity lamps.
Symptoms of Incorrect Lighting
Observe your plant closely to make sure it's getting the correct amount of light each day. If plants aren't getting enough light, they may turn pale green or yellow. This occurs because, without light, the plant isn't able to produce enough chlorophyll.
You may also notice that the plant is leggy and has stems that become thin and long as if the plant is trying to grow upward toward the light source. The part of the stem between the leaves may also elongate. The plant may drop leaves and fail to produce flower buds. Without flowers, your vegetables will be unable to produce fruit.
If your plants are getting too much light, the leaves may appear scorched or bleached. Brown tips and edges on the leaves may indicate that the light source is too close to the plant and is causing damage, advises the University of Vermont Extension. Be sure to evaluate other aspects of your plant's care as well to ensure there aren't other issues affecting plant health and growth. This includes making sure your plant is getting the correct amount of water and fertilizer and that it isn't suffering from disease or pests.
Other Tips and Considerations
Plants need both red and blue light to grow. Blue wavelengths enhance foliage growth and are good for starting seedlings and growing vegetables like lettuce. Red wavelengths are necessary for plants to produce flower buds and to prevent the plant from getting leggy. Many fluorescent lights produce mainly blue and green light, so be sure to check the label to make sure you are getting one that can emit a broader light spectrum for your vegetables, advises the University of Minnesota Extension.
Sunlight provides all colors of light, and you can more closely simulate it with a full-spectrum or broad-spectrum bulb. As an alternative, you can use a combination of cool lightbulbs that give off blue wavelengths and warm bulbs that emit more red wavelengths, notes the University of Vermont Extension.
If you want to be more precise about the amount of light your plants are getting, consider investing in a horticultural light meter, advises the University of New Hampshire Cooperative Extension. You can use this meter to measure the intensity of light the plant is getting to more accurately calculate where you should place the light and the number of hours it should run.
- University of Minnesota Extension: Lighting For Indoor Plants and Starting Seeds
- University of Florida IFAS Extension: Artificial Lighting for Growing Vegetables at Home
- Old Farmer's Almanac: Best Grow Lights for Growing Vegetables Indoor
- University of Missouri Extension: Lighting Indoor Houseplants
- University of Vermont Extension: Indoor Lighting For Plants
- University of New Hampshire Cooperative Extension: Growing Seedlings Under Lights [Fact Sheet]
Maureen Malone has been a professional writer since 2010 She is located in Tucson, Arizona where she enjoys hiking, horseback riding and martial arts. She is an outdoor lover who spends her weekends tending her raised garden and small orchard of fruit trees.