regularguy

Agent you are correct in what the figure would be.

choader

foot candles and lumen are the same.
You are mistaken to use lumen and not have your units match up

E=I/d^2 with d in FEET because of the measurement of the lumen by definition. So when you use a light meter to measure foot candles(E) at one foot it should equal the lumen rating for the bulb.(in theory but the bulb doesnt all point at the light meter) As the equation goes i may be wrong in that you need to multiply by 4pi(d^2) or something to get the area. but that would be for the light around the whole light at a distance d. I am fairly certain that the 4pi can be canceled out because you are just using a square foot on the sphere. So for E=9000 you can find the lumen by 9000*(1ft^2)= 9000 lumen. Im on summer break and really not functioning correctly so maybe when i sort that out i will try to do the same here.

choader

The meter readings recorded here are in lumens. Seems like it should be lumens/(some area unit). what is the area component?

Choader

Agent86

Hi Guys:

Maybe this will help.
I failed algebra so I'm not even going to try to figure this out.

I went back to the lighting store & held the light meter 1' under the center of the bulb, ( should have done this the 1st time, the sales guy's getting tired of me bugging him), & the lumens were only 6,100 not the advertised 8,900. It still seems like the lumens at 2 1/2" should be alot higher but I checked it again & got the same readings. By the way the meter he used has a digital read-out. He said they cost about $500.00. So I figure it must be a pretty accurate meter.

This doesn't mean the EnviroLights suck or anything, & it doesn't mean I'm going to go trade my lights in on another 430w hps, actually it really doesn't mean $hit. What's really going to matter is the dry bud weight. Remember, I think I'm the only one here who has already used the EVLs for a complete grow, and not under the best of conditions. I got 5.5 oz. from one 33"tall plant.

Like I said before I really don't know jack about all of this scientificaly, I just like the way the lights work for the size of my grow cabinet.

Later Grow Bros.
86.

__________________
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Trouble Shooting Guide ~ Educational Pictures ~ Guide to Successful Germination ~ Mite Tea
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While genius knows it has limits, idiocy is always unbounded.

regularguy

UHHH ithinki got it figured out

You do need the 4pi thing because of the sperical area we are describing. OK here we go again. I am going to relabel everything and you can disregard my previous post.
E=footcandles It is what you measure with the light meter.
I=lumens What the manufacturer gives you on the box.
A=area=4pi(d^2) with d in feet. This is where i went wrong.

OK so E=I/4pi(d^2)

E=19000 lumens at the highest reading.
d=2.5in/12in/ft=.208333ft

I=19000*4pi(.208333^2)=10362 lumens

There we go. Right on, if not a little high. Which im kinda glad about because the only reason i started researching lighting for indoors was because i want to start an indoor grow and im looking for the best light.

BUT we are only halfway there. We have more that we need to find out about this light and others.

1. You need to go back to the store and get the measurements for other CFL lamps to compare with.
2. We need to find out what spectrum all of this light is in. If it is all in the wrong spectrum than you wont have really dense bud. Also you have to count bud per lumen per day as it would not be fair to take 2 months of vegging and 3 months of flowering and compare it dead on with MH/HPS grows that were done at 1mo veg and 2mo flower.
3. We need to figure out how it actually compares to MH/HPS in actual lumens presented to the plant. I know heat and all that. So iwill try to work out a fair calculation to distances for MH/HPS setups from the plant at different distances and will post them when i get done. I will use standard lumen readings from reputable manufacturers such as philips.

I think we are finally getting somewhere
Also if anyone sees a shortcoming in the calculations let me know

regularguy

Agent

Judging from the shape of the EVL I bet with a reflector you could get the advertised 9000 at 1 foot. That is most likely how they measured them to get the results printed on the box.

choader

Here is some text I found at the following link:

"Light intensity Lab

"Light intensity is an indication of the strength of a light source. The SI unitof light intensity is the candela. The Onset HOBOs can be set to record using a variety ofdifferent units, but the most common choices are lumens per square foot or lumens persquare meter. A typical light intensity reading in a lighted room would be around 100lm/ft2(roughly 1000 lm/m2). When you move the sensor away from a point light source, you expect the lightintensity reading to decrease as you go. Specifically, light intensity should fall off as thesquare of the distance from the HOBO to the source.

For example, if you measure 2000lm/m2 with the logger 2 feet from a source, then you would expect to measure 500 lm/m2 when the logger is 4 feet from that source. If distance increases by a factor of two, then light intensity should decrease by a factor of four. The explanation for this relationship is simple. A point light source emits a given amount of power (we'll call this E for energy), which is spread out in all directions. The further from the source you go, the greater the surface area (SA) that the light source must illuminate. The power is evenly distributed across that surface area, so lightintensity at a distance r equals E/SA. Since the surface area of a sphere of radius r (theset of all points a distance r from the source) is proportional to the square of the radius(specifically, SA = 4r2), we get the equation:

Light intensity = k/r2(where k = E/4)

Thus light intensity falls off as the square of distance

Choader

Agent86

Regularguy:

That was with a reflector, in an open room.
Where the problem might be is that we were using a reflector made for 2 bulbs, ( like the one I have) instead of a single bulb.
I'm not going to bug the guy at the store anymore so just go with the 8900 lumens.

86.

__________________
Posting Guidelines ~ Grow Guide ~ Day by Day, Bubbler Grow Guide ~ The Library
Trouble Shooting Guide ~ Educational Pictures ~ Guide to Successful Germination ~ Mite Tea
The only difference between a wise man & a fool, is in the magnitude of his mistakes.
While genius knows it has limits, idiocy is always unbounded.

choader

If you know that you get 8900 lumens at 12", then can't you solve for initial lumens?

Choader

JoseHempSeed

the bulb puts out 8,900 lumens. by definition, that's total lumens, measured at the bulb.

so if you could somehow get all these lumens spread over just 1 square foot, you'd have 8.9k lu/ft sq.

reflectors don't add any light; they just direct the light you already have. there's NO WAY a light bulb that puts out 8,900 lumens can measure 19,000 lumens - at ANY distance, with ANY reflector - there just is not that much light to start with. you can't make light from nothing!

agent86, are you sure the meter measured lumens - not micro-candelas or something else???

choader

Is it 8900 lumens at:

a) the bulb, meaning total energy output
b) 12" from the bulb
c) some other distance

Maybe we should call them. Without knowing what 8900 represents, we are p*ssing in the wind.

As as aside, seems like a manufacturer would want to make it look as good as possible. That means 8900 is probably right at the bulb. However, there may be some industrial standard which defines what can be put on a label.

But that still doesn't explain the instore readings.

Choader

PS - I love this conversation. The EE in me is excited.