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Offlinezzzzzz
Stranger

Registered: 02/18/13
Posts: 136
Last seen: 6 years, 6 months
Re: The truth about leds [Re: zzzzzz]
    #660241 - 02/25/13 09:42 PM (6 years, 7 months ago)

I remember reading a very good article about light penetration and associated myths.  The easy way to check for truth regarding this is a light meter.  I don't have one but I do have an old SLR camera with light meter, which can be used.  The reason, for example, that the sun's rays don't diminish over the height of a plant is that it's so powerful and has already traveled so far, that 10 or 50 feet doesn't diminish the intensity (square of the distance ....).

I'm going to try to find that article and get back here.

Unless you or anyone has more factual information regarding this issue ....


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Offlinezzzzzz
Stranger

Registered: 02/18/13
Posts: 136
Last seen: 6 years, 6 months
Re: The truth about leds [Re: zzzzzz]
    #663749 - 03/27/13 05:54 AM (6 years, 6 months ago)

I thought these comments, from another forum, were thought-provoking.  I've had similar thoughts myself. 

"A question, I've been pondering for a while, for you to consider:

Background:

Most of the information below is from the "Marijuana Horticulture, The Indoor/Outdoor Medical Grower's Bible", 2006 edition, chapter 9 "Light, Lamps & Electricity" and I'm using "initial" lumens ratings for everything. Initial lumens are when the bulb is new and will decrease over time, not a measurement at the source as some have suggested. Lumens are what the plant "sees" and includes light that we cannot see.

Let's say that a one thousand watt HPS puts out one hundred thousand lumens (probably low, but it keeps things simple).

By definition lumen ratings are based or taken one foot from the source so (according to that inverse square law thingy), at twice that distance, two feet from the source, the lumens drop by three quarters, (one divided by two squared equals one quarter) to twenty five thousand lumens. At three times the distance, three feet, from the source, the lumens drop by eight ninths, (one divided by three squared equals one ninth) lumens for a total of eleven thousand one hundred eleven lumens, etc.

Now for my question, what happens when you move closer to, rather than further away from, the source?

Let's say I have eighteen, sixty-five watt CFL bulbs (total eleven hundred seventy watts going in, slightly more than the example above) rated at thirty six hundred lumen each, for a total of sixty four thousand eight hundred lumen.

Now, if I move these lights to six inches from the plants (one half the distance at which lumen measurements are taken), would the formula then be the same only with a distance of one half instead of doubled?

Due to the definition of a lumen, I cannot decrease the distance between the source and receiver below one foot and still call it a lumen. Or can I?

In this case the math indicates that at six inches(1/(.5 X .5)) X lumen rating goes up by four times. If calculated on a single bulb (lumen are based on single point sources), thirty six hundred lumens times four equals fourteen thousand four hundred "perceived by the plant" lumens. And with eighteen point sources that equals two hundred fifty nine thousand two hundred "perceived by the plants" lumens.

Wow, I gotta be wrong somewhere, how about it guys?

Let's see what happens (if my assumptions are correct) when the bulb is three inches (1/4D) from the plant... Wow again, sixteen times thirty six hundred lumens equals fifty seven thousand six hundred "perceived by the plant" lumens. And with eighteen point sources that equals one million thirty six thousand eight hundred "perceived by the plants" lumens.

What an I doing wrong here? Anyone?

I have six height adjustable rows of three bulbs surrounding five rows of two plants in a two foot by six foot closet. Recent temperatures are eighty two degrees in the canopy and seventy three degrees at the same distance from the floor outside the closet, using passive air intake (full louvered doors with three quarters at the top closed off) and a small fan in the ceiling (mostly to flush the odor).

From the first three plants, the largest bud/cola was nine inches around and twelve inches long. The second largest was very close to that.

I await any help on this subject as I'm growing, just not knowing. So many changes in lighting methods since my "bible" was published..."

So, since HPS lights have to be so far away and their light output diminishes significantly with that distance, is it possible fluorescent lights (CFL) CAN offer more light?


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