Light distance

Can someone post a chart of light distance, i need to know how the distance affects the lumes. i have a 250mh for veg in a 2x4 room and need to know at what height covers the room equally? thanks

Bumpbumpbump

Check this thread bro. Might shed some light on the topic. No pun intended. Gohydro posted the best chart I've seen yet. https://www.rollitup.org/indoor-growing/238649-correct-hieght-hid.html#post3044227

You may find this link interesting as well http://www.unitconversion.org/illumination/foot-candle-conversion.html

Thanks for the interesting chart, what i don't get is a 400w covers 4' x 4' but at what height they don't say anything about that.

reading those charts suggests that the height from the canopy should be 18" Mh and similar for Hps

It depends on your reflector... technically a 150watt HPS could cover 10x10ft, it'd just be dark as shit on the outside. If you want to cover 4x4 ft with a 400watt light, I'd say 18 inches away from the canopy.... but as I said it depends on your reflector and how much it covers the sides of the bulb. If the reflect or is mostly above the bulb, then it won't be in the way at all. If the reflector covers the sides a lot, you might have to move it even farther away because only a small angle of light is coming from below the reflector. You can't follow a chart with this stuff unless you know what reflector you use, but for a 400watt light and most reflectors... 18 inches should be good.

At 18 inches from the canopy:

The middle of the walls would be 2.5ft from the bulb and the farthest corners of the canopy would be just over 3ft away(which is still enough intensity to give decently sized buds at the top of the canopy, not considering any light that is still reflected off the walls).

Personally for a 400 watt light I do 3x3ft... but it all depends on how dense your plants are and how you're growing. With 4x4ft I wouldn't want my canopy any deeper than 9 inches... with a 3x3ft I'd say let it get 12 inches deep. Unless, of course, your plants are very bushy.

jonboy30 said:

reading those charts suggests that the height from the canopy should be 18" Mh and similar for Hps

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I have the vented reflectors with glass and I can keep them10-12 inches from plants..
the difference of the vented reflectors in night and day..I turned my lights on before I hooked up the exhaust vent and they were too hot to touch..now hooked up, there just warm to the touch as most of the heat escapes

I got WW growing right up against a 1000W HPS with glass. Let ur go man. The light distance thing is just something we all think we need to know. Let the plant decide how close it wants to be. 5 weeks 12/12.

downrivertrader said:

I got WW growing right up against a 1000W HPS with glass. Let ur go man. The light distance thing is just something we all think we need to know. Let the plant decide how close it wants to be. 5 weeks 12/12.

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Bad advice... keep the plant canopy 12-18 inches (any farther is kind of a waste)

personally I try to have mine as close as possible without heat stress. I got an indoor/outdoor thermo from Lowes, it mounts on the wall and gives a temp reading and humidty reading. It has a seperate sensor on a wire that is supposed to go outside to measure temp, but I mount it a few inches below my light to know the actual temp at the tops of my plants. It takes a lot of the guess work out, and only cost me about $12. I would highly recommend one.

Redeflect said:

Bad advice... keep the plant canopy 12-18 inches (any farther is kind of a waste)

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I think he said closer..not further away..

#1Raiderfan420 said:

I think he said closer..not further away..

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He did say closer... and I said don't put it that close. I said that was bad advice. Put it 12-18 inches away and not farther or else light is wasted.

Those were two separate things.

The point was not to put it as close as possible, 12-18 inches should be good, and any farther away is a waste.

downrivertrader said:

I got WW growing right up against a 1000W HPS with glass. Let ur go man. The light distance thing is just something we all think we need to know. Let the plant decide how close it wants to be. 5 weeks 12/12.

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I'd say were in the same boat. when i bought by 400w HPS and vented hood, it was hot! you could cook an egg on it. once I hooked it up to a 600CFM fan, it is cool to the touch. I would assume it is about 2-4 degrees above the external ambient temp outside of the grow room. Even with a filter attached, it hasn't changed at all. The plants are 1-2 inches from the glass.

It all depends on the external temp of the air being pulled into your grow room, the CFM of the fan pulling the heat from the reflector and how quickly your getting the hot air to it's final exiting point. Radiant heat from the bulb can also be an issue. so make sure you can move the cool air around the grow room.

If you don't have a vented hood, you will have to follow the guidelines for distances. Your plants will always let you know, and so can the back of your hand. if you put your hand under the light and it gets hot, your too close.

I have mine going in a 1'x2' closet and its in a cool tube 8" away. There is so much light in there its like im looking right at the sun..

msgmehere1 said:

I'd say were in the same boat. when i bought by 400w HPS and vented hood, it was hot! you could cook an egg on it. once I hooked it up to a 600CFM fan, it is cool to the touch. I would assume it is about 2-4 degrees above the external ambient temp outside of the grow room. Even with a filter attached, it hasn't changed at all. The plants are 1-2 inches from the glass.

It all depends on the external temp of the air being pulled into your grow room, the CFM of the fan pulling the heat from the reflector and how quickly your getting the hot air to it's final exiting point. Radiant heat from the bulb can also be an issue. so make sure you can move the cool air around the grow room.

If you don't have a vented hood, you will have to follow the guidelines for distances. Your plants will always let you know, and so can the back of your hand. if you put your hand under the light and it gets hot, your too close.

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I hear ya Bro...I have a couple 1000w HID,s ( switchable) and I did the same thing.. turned on the lights before I hooked up the exhaust.. you could def cook on them before and warm to the touch after..I am using MH right now and they are about 10" above, when I move to HPS I'll let the plants tell what they like

Motorbreath said:

personally I try to have mine as close as possible without heat stress. I got an indoor/outdoor thermo from Lowes, it mounts on the wall and gives a temp reading and humidty reading. It has a seperate sensor on a wire that is supposed to go outside to measure temp, but I mount it a few inches below my light to know the actual temp at the tops of my plants. It takes a lot of the guess work out, and only cost me about $12. I would highly recommend one.

Click to expand...

Spot on the exact same thing I do. Good call +rep