View Full Version : Height of Growlight

01-11-2009, 05:16 AM
I have a 400w HPS with a Phillps MasterColor CMH bulb. I have it about 2 1/2 feet above the tray, is this about right?

I am growing cumcumbers and tomatoes.

John M.
01-12-2009, 05:23 PM
The recommended height to keep a 400 W HID above your plants is anywhere from 12-24 inches. You can bring the bulb closer by air cooling your hoods and using a diffuser to lessen the hot spot directly below the bulb. Some growers use the back of the hand method to feel for uncomfortable warmth, though this would require you to do so constantly as your plants grow. Most will find a desirable distance and hang string as an indicator of when the bulb/hood should be raised.

02-22-2009, 05:28 PM
I had them at 12 inches when I started, but the 400 watt was just way too hot, I didn't have any ventilation fans....

John M.
02-24-2009, 01:32 PM
12" is a little on the close side if you are not working with an aircooled hood.

If you are not using an aircooled hood and still want to bring the bulb closer, a diffuser under the bulb does an excellent job of misdirecting the "hot spot" so that your plants can withstand being closer to the light source.

02-27-2009, 06:49 AM
thanks John, I have since brought the light up higher, going to look into a diffuser.....