Indoor plants are a great way to extend the growing season and bring a bit of the outdoors inside. Grow lights are commonly used to supplement or to replace natural lighting for indoor plants with low to medium lighting requirements. Plants that can't tolerate direct sunlight also benefit from the use of grow lights.
Fluorescent Grow Lights
Fluorescent grow lights are the most common type of grow lights. Fluorescent bulbs are cheaper and provide a healthy amount of lights to plants without the risk of burning them. Because they produce less heat than other types of grow lights, they can be placed within inches of the tops of plants. Fluorescent bulbs labeled as T-5 are a good choice for primary light sources because they are smaller and able to provide more concentrated lighting. Grow lights using T-5 bulbs are great for shade-loving plants and young plants. Indoor gardeners should choose cool-white fluorescent bulbs, which produce a slight amount of red rays in addition to blue, green, yellow and orange light rays.
HID Grow Lights
High intensity discharge (HID) lights are another highly efficient way of providing indoor plants with artificial lighting. There are two main types of HID lights: metal halide (MH) and high pressure sodium (HPS). HPS indoor grow lights provide orange or red light, which stimulates flowering. MH grow lights are more suitable for stimulating shoot and leaf growth because they provide light in the blue spectrum.
Incandescent Grow Lights
Incandescent grow lights are generally used only to supplement the light of individual plants that receive some natural sunlight. Incandescent grow lights tend to be some of the most expensive and least effectual grow light systems. Incandescent light bulbs give out a lot more heat than they do light, and it is difficult to get the light close enough to the plants to meet their lighting needs without burning foliage.
Mercury Vapor Grow Lights
Mercury vapor grow lights are an expensive option for serious indoor gardeners who cultivate a large number of plants. Mercury vapor light bulbs give out more light and less heat than incandescent bulbs, which makes them effective primary light sources for indoor plants.
Grow lights should be placed where they will provide plants with the most light without burning the leaves and flowers. Incandescent grow light should be placed about 1 foot away from plants when using a 25-watt bulb, 2 feet away with a 100-watt bulb, and 3 feet away with a 150-watt bulb. Mercury vapor grow lights are usually placed about 5 feet away from plants.
Indoor plants typically need grow lights for 12 to 16 hours every day. MH lights should be run between 18 and 24 hours each day to promote foliage growth. HPS grow lights should only run for abut 12 hours daily in order to create the optimum light conditions for budding and flowering.
Plants' growth patterns indicate whether their lighting needs are being met. Symptoms of light deficiency include long stem lengths between leaves, little to no plant growth, smaller leaves and a lack of buds or flowers. Some plants turn pale green in color and leaves might yellow and prematurely drop.