Choosing the correct grow light for the needs of your specific plants is essential to success. Too much light can burn or dry out plants, and too little light can cause stunted growth and even the death of the plant. Budget and energy use concerns should also be taken into consideration.
Know how much light the type of plant you're growing needs. While some plants might be fine with a regular fluorescent tube, bright-light lovers may like some thing a little more intense, such as a compact fluorescent, and full sun lovers usually need a high intensity discharge (HID) lamp to meet their optimal growth potential.
The larger the growing area, the more lights you need to cover every square inch. For small areas like a shelf or table top, a T12 or T5 strip light is usually sufficient. Pendant lamps are available with square- and round-shaped bulbs for smaller spaces. Large growing areas need high wattage HID lamps, such as metal halide or high-pressure sodium, to spread the most amount of light while using the least amount of energy.
Kelvin rating measures the relative whiteness of the light put out by the bulb. For optimal growth, a daylight lamp with a slightly blue heavy spectrum is best at 6700K. Lower Kelvin ratings such as 2700K are in the red spectrum and contribute to reproductive growth, higher ratings above about 4200K are in the blue spectrum and contribute to vegetative growth.
Some lighting is more efficient than other types, meaning it puts out more usable light per watt burned than others. Compact fluorescent T5 tubes put out several more times the amount of light than a standard T12 tube of a similar wattage but cost more to set up. HID lighting is one of the most expensive options; however, it covers the largest area, so one HID lamp can do the same job as several T5 fluorescent tubes.
Growing areas often have dark and shaded spots at the edge of the reach of a large light. Areas like this can be supplemented with a smaller wattage or different types of lighting entirely to make up for dark spots. A blending of color temperatures is often needed using several different bulbs to create the perfect blend of red and blue for a specific plant's needs or to create a change of season effect and initiate reproduction.