Anyone have a formula for....

[davejohnwright]

Anyone have a formula for loss of lumens due to distance? I found one that I'm not quite sure about.

davejohnwright Reviewed by davejohnwright on 07-08-2007. Anyone have a formula for.... Anyone have a formula for loss of lumens due to distance? I found one that I'm not quite sure about. Rating: 5

[rhizome]

Morning Dave-

It's a function of the inverse square law. Here's the math, as we know you love numbers Sorry, couldn't seem to get a clearer thumbnail. ( Note- edited to include better thumbnail)
Chart looks bout right to me. Don't forget to allow for reflection- inverse square is only a clean calculation if there's no reflective light. If you were to build the space up and then sample w/ a light meter, you'd find that the math holds good until the plane where reflective intersects direct, @ which point they reinforce. You'll find smaller than predicted loss of intensity as you move lower in the space- still there, but the loss ceases to be purely porportional and becomes somewhat fractional, as the level of reflective has an inverse relationship with the level of direct.

Intensity i @ distance r=

[the image reaper]

here's the short, simple version, for us dumb guys: "the closest the plant can get to the light without heat damage, the fastest the plant grows"

[davejohnwright]

Thanks Rhizome, I'm trying to rethink how tall I can let plants get under my light without the bottom branches getting to little light.

[oldsanclem]

A good parabolic reflector helps

[davejohnwright]

Im gonna save a buck and use the hood I already have. Besides a 1000w puts off alot of heat, and I've never seen an air cooled parabolic.

[Weedhound]

Buy yourself a nice cheap handheld temp gun....tell you exactly how close you can put your light to keep leaf surfaces under 80 degress....which I am told is optimum.

PS...I'm told by the same source....(who knows his shit btw) that that is how the "pros" do it......with a light meter and temp gun which will tell them max watts per sq foot so I'm not sure there is "one" right formula for plants.

[oldsanclem]

Note one way to suck heat off a parabolic is to place alm. vent at the top of the fixture and use a bathroom 70 cfm to pump out the extra heat.
I used on with a suncircle with a 1000 watt MH and a 400 watt hps. The vent temp was about 15 degrees differance between room temp and venting temp.
The room was about 20% less time on a normal venting time.
I use a single bulb system now, as very little co2 get picked up by the vertical heat rising from the bulb. The tanks last about the same amount of time. A extra advantage to the heat pump is it warms up the grow room and clone space.

[the image reaper]

Thanks Rhizome, I'm trying to rethink how tall I can let plants get under my light without the bottom branches getting to little light.

if you have room, try this trick: ... awhile back, a friend (Custom39), came up with the idea of placing his pots on a 30-degree angle ... he built a false-floor, but you can just 'block it up' with a piece of wood, under the bottom of the pot instead ... every day, he would spin the pots 1/4 turn, resulting in the whole side of the plant being exposed to the light, as well as the tops ... check the pic for the result ... that plant was only 30"-32" tall, but yielded 7 ounces of DRY buds ... I'd be doing it that way too, but my cabinet is too 'tight', not enough room to lean my plants over ...

[rhizome]

Cool trick. Thanks.