Agent86

Using the chart below tell me if there is something wrong with my calculations.

If you take a measurement 1" from the bulb wouldn't you need to divide the reading by 144sq. in. to show what the lumens are over 1 sq.ft. at 1" from the bulb. Then you would need to figure out how much of the surface area of the light is shining directly onto the square foot of space you are measuring. You would then take this answer & multiply it with the sq.in. to lumen answer.
Here is an example.
A 95w EVL is approx. 36sq.in. 12"Lx3"W
56,700lumen@1"/144sq.in.=393.75x36=14,175 lumen at 1" over 1sq.ft. with a 95w EVL centered over the sq.ft measured.
You would need to test the lumens without a reflector for this to be somewhat accurate.
In other words we need to take into account how much of the surface area of the light is shinning on the light meter when it's only 1" away from the bulb. The above calcultion only works if you assume that the lumens your measuring at 1" came from 1sq.in. of the output of the bulb.

Lumens of 95w full spectrum EVL with reflector.
1' = 3,780 lumen
10" = 8,820
8" =11,340
6" = 15,120
4" = 22,680
2" = 37,800
1" = 56,700

Does this make any sense or am I just really high & up to late?

Later.
86.

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JoseHempSeed

hey agent86

i think you're making things harder than they really are.

it can be a little confusing...especially when you really look at some of the details...but if you just forget about everything else and start over...

1 foot-candle is the same brightness as 1 lumen per square foot.

so if you measure 57,000 ft-candles, that's the same as 57,000 lumens per square foot. whether you're 1 inch away or 1 foot away or 1 millimeter away.

now if your lamp actually illuminates the entire 1 square foot area with the same 57,000 foot-candles (57,000 lumens per square foot), is another story. i think that's your question?

Agent86

Hi JoséHempSeed:

1 foot candle does not = 1 lumen
1 foot candle = 12.6 lumen.

What I'm trying to say is that what my meter measures 1" from the bulb won't be the same over 1 sq.ft. unless the light is also 1sq.ft. Since the bulb is not 1sq.ft. you are going to have a diminishing amount of light towards the outer edge of the 1sq.ft. you are measuring.

Make since.

Later.
86.

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JoseHempSeed

that's correct. 1 foot-candle is the equivalent brightness as 1 lumen per square foot.

that's correct, too, but ONLY if you are measuring your light source 1 foot away. and by the definition, you MUST be measuring a candle!!!

you're making this way too hard...

Agent86

Ok Jose':

I think I'll just stick to mist's theory.
[quote]
Light grows plants good, keep light, light grows plants bad, throw out light, get new one.

But I still think we are missing something.

Later.
86.

__________________
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While genius knows it has limits, idiocy is always unbounded.

denspot

"One Lumen is equal to the amount of light emitted by one candle that falls on one square feet of surface one foot away."...

"One foot candle equals the amount of light that falls on one square foot of surface one foot away from the candle."

And there you have it...

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powercow9

and another def for lumen
Lumen: by definition there are 683 lumens per watt of radiant powercows at a wavelength of 555 nm

just feeling silly trying to confuse things. First I am most impressed with your light reading agent86 and I really could care less if it is in lumens or foot candles or whatever.. I still think it's only one small part of light.. I think cri and kelvin and luminous efficiency have alot to do with it as well.. ( but i do like the comparison of the enviro's at 1" and the hps at 1') From the looks of agent86's grow.. the envirolights lights arnt be half bad and I guess product really matters.... I also wonder about bulb life concidering their expense.

Last have any of you ever concidered sad-lights.. for people with winter depression.. supposed to be 10000 lumens/m2 with a cri of 98..checkem out here.http://www.sunalite.com/s_lightboxes.cfm

ps
1 lux = 1 lumen uniformally distributed over the are of 1 meter.. and since we are all using feet here.. I figure I'd leave it to you all to scratch you head with.


pps

powercows translates to power for most of the rest of the world.

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denspot

- so wait a minute... does one lux = 12 powercows/ sq ft. or 41.8 powercows/ sq. meter???

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regularguy

OK all
Ive got a job and stuff so i had to drop out of the thread for a bit as my real life called. Using the proper equation

I=L/A

with
I Illuminance
L lumens
A area of sphere = 4pi(d^2)

the actual lumens put out at the following foot candle readings varied. It shouldnt and i will give my reasons and presumptions later.

One EVL
inches foot candles Lumens of bulb
12---------300------------------3770
10---------700------------------6100
8----------900------------------5025
6 ---------1200------------------3770
4 ---------1800------------------2515
2--------- 3000------------------1050
1--------- 4500------------------3925

2 EVL lights
inches foot candles Lumens of bulb
12 ---------- 875------------------10995
10 ---------- 1250------------------10900
8 ---------- 1500------------------ 8375
6 ---------- 1800------------------ 5655
4 ---------- 2500------------------ 3500
2 ---------- 3000------------------ 1050
1 ---------- 3300 ------------------ 2880

Now, none of the calculated lumens come out to equal the advertised lumen reading. I would guess that if you take the average and disregard the readings 4 inches and closer,see reason 2a, you get an average lumens of 4500. And for 2 bulbs, 9000.


OK the lumens for the bulb should have all equaled the same number but they don’t for various reasons.
1.human error in measurement
2.hot spots from the reflector
3.too close to the reflector and it is not a sphere you are measuring anymore
4.The bulbs measured were old
5.The output of these lights is not in the green spectrum so the light meter doesn’t measure it "correctly". I am doubting this one because either mist or agent said that the EVL appeared so much brighter than a MH lamp. The brightness would indicate more output in the green than the MH lamp.


Reasons that the readings were either too low or too high.
1a.The reflector makes it only part of a sphere. This would make the measurements given the highest possible because you are intensifying the light where you are measuring and then saying that it is that intense over a sphere which it is not.
2a.They would be wrong altogether at the close distances to the light because you cant make a sphere around a point source if the point source is bigger than the sphere you are making.

HPS readings
feet foot candles lumens
1 ----- 2250----- 28200----- 400hps
2----- 5000----- 252200----- 600hps
2----- 5200----- 261250----- 1000hps
1----- 180----- 2260----- 40w flouro
.0833--3700----- 3872----- 40w flouro

Same notes about the readings appy to these also.

Comments?
Who knows HTML and how to insert blank spaces inbetween text?

denspot

What???
those numbers don't make sense!!! Or am I just wasted....
Huh???

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