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Metal Halide Grow Lights

Metal halide grow lights have been the choice among professional growers of basil for many years. As far as high-intensity discharge lamps (HID lamps) are concerned, metal halide (MH) produces the most desirable light spectrum for growing basil – blue light. Light that falls within the range of blue light, around a wavelength of 475nm, is best for plants that are in the vegetative state (meaning that they are not yet flowering). Basil becomes bitter to the taste once it starts to flower, so we are mostly interested in using the blue spectrum for most of our growing.

The Light Balance

Growing Basil Light Spectrum

However, like everything in life, it is good to maintain a healthy balance. Studies have shown that basil grown with red light wavelengths have larger leaves with more water content. This suggests we shouldn’t disregard other wavelengths of light, as this will help bring out some very desirable attributes in our basil plants. For growers who strictly use metal halide grow lights, having some natural light coming from windows would be helpful to provide some of those other wavelengths. If no natural light is available, fluorescent lighting can be used to supplement. By using a metal-halide light system for growing basil you can expect to see leafy and compact growth of the herb. Adding some red light will cause it to grow more leggy. For more information about the wavelength study see my article Artificial Light for Growing Basil.

Hot Stuff
MH lamps are powerful and efficient, but they also get very hot. The lamp is essentially a tube that contains mercury, argon and some halide salts. When voltage is applied across its electrodes, the heat generated by the arc vaporizes the gas and salts into a plasma. Temperatures inside the tube can get to be 3000 degrees Fahrenheit. Never touch the bulb or the enclosure as it can reach several hundred degrees during operation! When you get a MH bulb you will need to purchase an electrical ballast as well. The ballast regulates arc current and makes sure proper voltage is applied to the bulb at all times. These lights give off some serious heat, so you will need to hang them several feet above your basil plants to avoid damaging them. If you are growing in a small space which is poorly ventilated you may want to consider getting an air-cooled hood for your setup.  These specially designed hoods come with air vents that normally fit a standard 6″ exhaust fan system. Another alternative for small spaces is to use a LED grow light system instead of metal halide.

MH Wattage Coverage (sq. ft.)
1000w 64 sq. ft.
400w 16 sq. ft.
250w 6.25 sq. ft.
100w 1 sq. ft.

Light Coverage
Metal halide grow lights are quite efficient and are difficult to beat, even by new LED grow light technology. MH bulbs put out approximately 125 lumens of light for every watt consumed. Compare this to 39 lumens per watt, as produced by regular fluorescent grow lighting. A standard bulb will provide about 10,000 hours of regular use before needing to be replaced. As for coverage, a single bulb can cover a large space. A 1000w grow light can cover 64 sq. ft. A 400w grow light can cover 16 sq. ft. and a 250w grow light can cover a little over 6 sq. ft. Most people don’t go below 250 watts with MH.

If you believe metal halide grow lights are for you, one cost-effective solution is the 400 Watt Super HPS MH Grow Light System.  Please note, this is a link to a product being sold on and I do get a commission if you buy through this affiliate link. Thanks in advance and happy growing!