SELECTING THE CORRECT  GROW LIGHT

Hydroponic gardens usually supplement or replace natural sunlight with specialized “grow lights” designed according to the parts of the light spectrum plants need most. What type of grow light (or combination of grow lights) you need will depend largely on what plants you are growing, and what plant behavior you’re trying to encourage.

To understand the concept of grow lights, it helps to know a little bit about color temperature and how it affects plants.  When referring to “temperature” with plant lighting, we aren’t talking about heat, but about color.  The color spectrum is measured in degrees Kelvin, just as some applications of heat and cold are—except higher temperatures are considered “cooler”, and lower ones are “warmer.”  The temperatures ranging above 5000K most resemble the intensity and color of sunlight, and are blue on the color spectrum.  The yellows, oranges and reds are actually lower temperatures, 2700K and below.  The significance of this spectrum is that flowering and fruiting plants tend to do better under slightly cooler color temperatures—usually around 4800K, which is still considered in the “blue” zone—but leafy vegetation does better in the 6000K range (essentially full sunlight).  Furthermore, when plants are flowering and reproducing, they are drawing more from the orange-red color temperatures, around 2700K.  So you can see why the right grow light setup can be so critical.

The three most common types of grow lights used in hydroponic gardens are designed toward the color temperatures most needed by plant life.  One of the most  popular types is the Metal Halide bulb.  A High-Intensity Discharge (HID) bulb, Metal Halide bulbs range from 2700-5500K and are the closest to true sunlight that money can buy.  These are especially good for leafy plants.

A second option (also a HID bulb) is the High Pressure Sodium bulb.  These bulbs emit the orange-red part of the spectrum (around 2200K) and are good for flowering, but don’t encourage full foliage.  They are not generally used by themselves, but in combination with other bulbs and/or natural light.

The third most common bulb is the fluorescent—either high-output (CFL) or low-output.  Not as intense as the HID bulbs, they can still cover the spectrum well, with the added advantage that they can be placed close to the plants because they emit so little heat.

In more recent days, LED bulbs have been designed, some of which claim to cover the full range of color temperature for plant life with almost no heat.  However, they are quite expensive, and in some circles it’s believed you can achieve the same results with the lesser expensive fluorescent bulbs.

For most hydroponic grow rooms, different bulbs are combined to cover the full spectrum of blues and orange-reds that plants need for various stages of growth—although leafy plants will lean more heavily toward the blues.  Your retailer will be able to advise you on what grow light combination will be best for you.