Low Pressure Sodium lights for growing marijuana?
Marijuana is only growing one to three leaves instead of five to eleven is it normal?
September 4, 2010How can I get a medicinal marijuana card for depression?
September 4, 2010
Zach asked:
If there was just one or two plants trying to be grown would a 75 watt LPS ( Low Pressure Sodium ) light work and how far would it have to hang above the plant? If it would not work what type of lights would? (specific) Thank you.
2 Comments
High intensity discharge (HID) lamps like yours are very bright so a 75 watt LPS light would be plenty of light for a couple plants. There are a couple things to remember though. Light intensity decreases with the square of the distance (inverse square law), so if you have 50,000 lumens at a distance of 1 foot, and you double the distance to 2 feet, the intensity will be 1/4 or 12,500 lumens. If you double the distance again to 4 feet, the intensity is 1/16 or 3,125 lumens. So you see it is important to have the light close if you want the most intensity.
BUT, HID lamps are very hot. And if you increase the intensity with a reflector, you’ll be reflecting the heat toward the plant also. This means you have to keep the lamp farther from the plant to prevent burning.
Therefore, the distance you use depends on the wattage of the lamp, the type of reflector, the intensity of light you want, and how much heat the plants can take.
Personally, for plants I grow indoors during the winter, I use 100 to 500 watt compact fluorescent lights in dish shaped reflectors. Fluorescent lights aren’t as bright, but because they are cool, you can have them as close as 1 inch from a plant without harming it. They also don’t need a special power supply like HID lamps.
You can see the different spectrums of low pressure and high pressure sodium lights here:
There’s a reason folks use HPS lights. As you can see, the spectrum is much broader and thus better for your plants. Plants need light from the blue end as well as red, and LPS lights have little if any blue. In general, the more light, te better production of buds. For just one or two plants, I’d use a 400 watt HPS hung 12-18 inches above the canopy.