How far should your lights be from the plants?

[Myztery]

Hi all,
this is my first time growing in maybe 3 or 4 years. I have a hydro NFT veg cab built already and I am now in the process of drawing out the blue prints for my flowering tent. When I grew before, I moved the plants from my previous veg cab directly outdoors because where I am its natural 12/12, 24/7. Which is why I never had to deal with HPS lights etc. Therefore, I would like to know the safest distance apart from the lights to the top of the plants which would not burn the plants or cause any problems so I can work out what the height of my tent should be. Thanks all.

Keep it green =).

 

[Myztery]

p.s. I forgot to mention that I will be using a 400w HPS light but I would like to know the difference between 600w and 1000w in case I ever change my lights. =D

 

[guineapig]

A 400 watt light allows for a closer distance between canopy and bulb than higher wattages.....

Here's a trick you can do which will help answer your question:

Turn on your light......place the palm of your hand 2 feet below your bulb, face down, so that the light from your bulb is now shining directly on the back of your hand......slowly move the back of your hand upwards towards the bulb......ever so slowly, inch upwards.....slowly.....now when you notice that the back of your hand has begun to feel so uncomfortable, on the verge of painful, then you have found the spot where the canopy should not exceed......

factors like air-cooling your reflector and using the UV glass shield will slightly affect this distance, but do this test for yourself whenever you need to know the optimum distance between the canopy tops and the bulb......

One other thing to remember is that some of the reflectors on the market (usually the cheaper ones) can create "hot spots" where defects in the sides of the reflector concentrate light (like a magnifying glass)......flowers can get burned this way......the burned parts of the flowers are concentrated in a very small area, and flowers next to and below the burned flowers are unaffected and growing just fine......thats how you know you have a "hot spot"......it is possible that defects in the bulb itself could cause these "hot-spots," and i personally fear that the influx of Chinese-made HID bulbs has the potential to cause an increase in grower-reported "hot-spots"......however, although i have no direct evidence of Chinese-made bulbs causing this problem, i absolutely have heard stories of these "Chrome Dome" bulbs (with a reflective surface built into the bulb housing) causing all kinds of problems......melted bulbs, improper firing of bulb, etc......so these days, i try to buy the more expensive bulbs......(i guess i'm getting off-topic, but i'll start a thread comparing all the different kinds of bulbs)

Hope this helps!!!!! sorry for the tangent.....

kind regards from guineapig

 

[BeeBee]

I have a lot of experience with 600 watt hps. The bulb can be as close as 10 inches to the nearest vegetation. That gives the same intensity as noonday sun at the equator.
I usually have the bulb 12 to 14 inches from the vegetation, once the plants have adjusted to the high-intensity.
From what I've read, a 1000 watt light needs to be 1.5 times as far as a 600, so 15 inches at the closest, and 18 inches for normal, very-high-intensity illumination.
I like high-quality, standard HPS lamps, made in Europe, such as GE, Sylvania, Philips or their horticultural cousins which cost 10 to 20 per cent more.
Having good air-circulation under the lights reduces hot-spotting. Often, increasing circulation is a better choice than raising the light, when slight leaf-burn is noticed. Furthermore, some burning is tolerable, when not too severe, so that lower parts of the plant are able to continue to receive the benefits of high light intensity.

 

[Myztery]

Thanks for all the help guys. Really appreciate it =). I have decided the height for the tent should be 2.2m tall.