Metal Halide:

Metal halide (MH) grow lights are a type of high intensity discharge (HID) lights that are used for plants in the vegetative growth stage. Metal halide bulbs produce light in the blue spectrum which is close to the intensity of natural sunlight. This is positive since grow lights are replacing or supplementing natural sunlight. Using the proper wattage an intensity of metal halide grow lights will ensure optimal vegetative growth in plants.

Fluorescent lights are sometimes used for vegetative growth instead of metal halide because they burn cooler. However, fluorescent lights cannot match the intensity of metal halide grow lights. This is why metal halide grow lights are typically preferred over fluorescents. Although, if cooling and ventilation is an issue, metal halide grow lights may not be the best option because similar to high pressure sodium bulbs, metal halides burn very hot. It is important to take care to ensure metal halide bulbs are properly cooled and keep the tops of the plants away from the bulbs or they may burn. Air conditioning units are often needed when using HID lights – both metal halide as well as high pressure sodium.

Similar to HPS lights, metal halide bulbs come in different wattages, and some can be used horizontal, or vertical, or even both (universal). The most common metal halide bulbs used in indoor gardens are 250 watt, 400, 600, and 100 watt. A ballast is needed to operate all metal halide bulbs, so be sure to use a ballast that is the same wattage as the bulb. A single 400 to 600 watt bulb can support up to 4 plants, and a 1000 watt bulb can support between 6 and 8 plants. <

If the heat can be managed, metal halide grow lights will allow plants to grow quickly and vigorously in indoor gardens. Metal halides can take young seedlings all the way through the vegetative cycle until they are ready to be switched to high pressure sodium grow lights to begin the flowering stage.