Grow Light Basics, Part 1: Bulbs and Coverage



Thinking about starting your first indoor grow? It’s easier than you may think.

In this first of a multi-part series on grow lighting, we’ll consider the different types of bulbs available and their respective benefits. In future installments, we’ll consider fixture and reflector types before moving to peripherals, including ballasts, timers, and controllers.


Color Temperature and the Plant Life Cycle

English: Kelvin Temperature Chart

Most plants go through a growth (also known as “vegetative”) stage and a flowering (also known as “budding”) stage. Each stage thrives under a different part of the light spectrum, represented by color temperature.

Lights with a color temperature of 5000 Kelvin or higher produce the blue part of the light spectrum and are ideal for the growth stage of your plants. Lights with a 2000 Kelvin color temperature, on the other hand, produce light in the red spectrum and are essential for the flowering stage.

HID vs. Fluorescent

To artificially create light within the right spectrum for your plants, you have two choices: HID grow lights or fluorescent grow lights.

HID lights are most common in grow lighting. To produce the red and blue spectrum with HID lights, you need high pressure sodium (“HPS”) lights and metal halide lights, respectively.

Linear fluorescent grow bulbs come in T12, T8, and T5, each more efficient and compact than the one before it. Today, T5 lights are used almost exclusively. Fluorescent lamps also come in a variety of color temperatures, so look for the right Kelvin rating before you buy.

Calculating Coverage

But how many bulbs do you need and of what wattage?

Coverage varies depending on the type of bulb and fixture you use, but at least as far as HID lighting goes, the “rule of thumb” is 50 watts per square foot. In lumens (the standard measurement of light output), that comes to about 1,500 lumens per square foot for metal halide lamps and 2,000 lumens per square foot for HPS lamps.

Fluorescent coverage is less precise and determined as much by the fixture as by the bulb itself. Unlike HID lights, fluorescent tubes run so cool you can place them as close to the plants as you want. This means the coverage of a fluorescent grow light is roughly the same as the dimensions of the lamp itself.

For more examples, check out our grow light coverage infographic:

Grow Light Coverage

Grow Light Coverage

Looking Forward

Next week, we’ll look at grow fixture and reflector types more closely. But if you just can’t wait, reach out in the comments section below or on Facebook, Twitter, or Google Plus. We’re happy to answer your questions anytime!

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Benjamin is a writer for 1000Bulbs.com.

  • Paul COPPAGE

    Go, Mr. Rorie, go!! – Paul C.