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The Different Grow Room Lights and How You Use Them

Part II: Metal Halide Lights

Growing facility with HPS lights and Quest Dehumidifiers hanging from the ceiling

HID lights, or High Intensity Discharge lights, are among the most popular of the grow room lights. That’s because they are proven to be effective, are cost-efficient, and provide the best yields among grow lights on the market.

There are two different types of HID lights: Metal Halide (MH) and High Pressure Sodium (HPS). They work as a team; each is used in different phases of plant growth.

In this article, we’ll talk about MH lights.

How MH lights work

MH lights pass an arc of electricity through a mix of gases (mercury, metal halides, argon) to produce light. The halide mix influences the light’s color, the amount of heat it produces, and its intensity.

MH lights considerations

MH lights’ advantages far outweigh any disadvantages, but they do have one major disadvantage over some of the newer light sources: They’re hot.

Grow room temps should be kept between 68° and 77°F for cuttings and seedlings, and no hotter than 82°F for older plants when grow room lights are on. Because MH lights produce so much heat, you may need to exhaust some of that heat to keep temps within the desired ranges.

In addition, they need ballasts to operate, so they can be a little costly at setup. They are very cost effective lighting options after initial setup, however.

MH lights advantages

Best “blue light” source for robust vegetative growth

Of all light choices, MH is the most efficient for growth because it comes closest to emulating bright summer sunlight. It is in the “blue light” spectrum. It’s the only light source that can offer the kind of intensity plants need for vegetative growth. Your plants will love this “sunlight,” and that will encourage photosynthesis. Choose MH lights that are about 6500 Kelvin (K). (Kelvin is the measure of a light’s color “temperature”: the higher the Kelvin value, the “bluer” or “cooler” the color temperature.)

Long lasting

MH lights last a long time and won’t diminish as much as some other types in “lumens,” or light intensity, as they age. You can expect, for example, that a MH bulb will still have about 85% of its original intensity after a year of daily use. (Do replace them once they drop to about 85% intensity, so that plant growth stays robust.)

Easily replaced

MH bulbs are easy to find, competitively priced, and easy to replace in your grow room setup.

Proven results

While there are some new lighting options out there, none are tried and true. MH grow room lights are an industry standard, with proven results.