Plants require a balanced light source to make the energy needed to grow; however, when they are kept indoors they are often deprived of this balance. Natural sunlight contains all the colors of the light spectrum, including the red and blue rays that plants use most frequently for photosynthesis.
Artificial light from an indoor light fixture often is not sufficient for plant growth. Plant lights create balance by supplying the plants with the rays they need to thrive. There are different types of plant lights, which can be used to address the diverse needs of plants.
Fluorescent bulbs are one of the most common types of plant lights. Mainstream fluorescent grow lights put out a high concentration of blue rays, but special bulbs have been developed for growing purposes that also release red rays.
Many indoor gardeners favor fluorescent bulbs because they are much cooler than other light sources. This means that the fluorescent plant lights can be placed closer to the plants without the risk of damaging them. In return, the plants are able to absorb more of the needed rays. They work particularly well in rooms that have little to no exposure to natural light.
Metal Halide Bulbs
Metal halide bulbs produce a very concentrated supply of blue light. They are best used in areas where they will be the plant's primary light source (such as basements). They encourage green, leafy growth in plants and generally keep them compact. They are good for tropical plants that do not flower; however, they can be expensive and are not as readily available to the average home gardener as fluorescent bulbs.
High-Pressure Sodium Bulbs
High-pressure sodium bulbs mainly emit red light. They are best used as supplemental lighting alongside natural sunlight (such as in greenhouses). High-pressure sodium bulbs encourage flowering plants to bud and bloom; they cannot really be used to start or maintain young plants, as they do not provide the necessary blue rays for them to flourish.