A greenhouse located in an area with insufficient sunlight may require a supplemental lighting source for optimum plant growth. Choosing the best greenhouse lighting usually requires a general knowledge of the light spectrum and the color range provided by various bulb types. Fluorescent greenhouse lighting is an inexpensive option that produces light in the blue or red spectrum depending on the type of bulb chosen. High intensity discharge lighting is available in a blue-light producing, metal halide version or a red-light emitting, high-pressure sodium bulb. Traditional incandescent bulbs are usually inefficient and hot, while light emitting diodes (LEDs) often give vegetation an unnatural appearance in natural sunlight.
Plants generally require light from the entire spectrum for proper growth. A greenhouse should be positioned in a way that allows plants to absorb as much sunlight as possible. Greenhouses located beneath a canopy of trees or in the shadow of a larger structure usually need some form of supplemental lighting. Choosing the best greenhouse lighting often requires a basic understanding of the type of light produced by various bulbs. Red-spectrum light typically produces the best results for flowering or fruit-bearing plants, but blue-spectrum lighting must also be present to prevent vegetation from growing too tall or thin.
Fluorescent bulbs can be a good greenhouse lighting choice when cost is an important factor. These bulbs are sold in a blue-light emitting, cool-white version that is very effective for seedlings and short plants. The warm-white version emits red-spectrum light that is appropriate for flowering and fruit-bearing plants. These bulbs emit a low-intensity light and produce very little heat. Fluorescent bulbs are typically placed in close proximity to the plants for optimum results.
High intensity discharge bulbs work very well for larger structures, but can also be expensive. Despite their initial higher cost, these bulbs are a long-lasting and energy-efficient greenhouse lighting method. They are available in a metal halide or high-pressure sodium version. Metal halide bulbs are often used as a primary lighting source and produce blue-spectrum light. Red-spectrum emitting, high-pressure sodium bulbs have an orange glow and are typically used as a secondary lighting source.
Conventional incandescent bulbs are usually a poor choice for greenhouse lighting. These bulbs emit red-spectrum light, but are generally inferior to other lighting methods because of their low intensity and high heat output. Incandescent bulbs may be utilized as a secondary lighting source when placed at a safe distance from the plants. LEDs are not recommended for greenhouse lighting purposes. These bulbs tend to give plants an abnormal appearance when viewed in natural sunlight.