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Oh and if you have anything to add to the article that could give more insight please pm me explaining it as somone helpful has already done and we can discuss it or extend the article. I think this thread should be for people to input on eachothers ideas and improve on them until we have a reached a final decision on a way to calculate the light. THEN a new thread can be made with the exact way to do it and it can be stickied.
not a very close approximation , remember that the formula that you use is for a pountual source of electromagnetic radiation , the lamps are not , especialy fluorescent tubs.Originally Posted by [b
The calculation made like you presented will give a much higher value than the real one.
Elandolf - thanks for the thread, as I’m also interested in the amount of light my setup delivers. I have four 2000 lumen lamps about 10” from the top of my pots and based on your post I figured I’m around “Cloudy Bright”. I decided to check the numbers with my SLR camera.
I got a white sheet of paper, drew a cross in the middle, set my camera to F22, set it to Aperture priority (so the camera would pick the shutter speed), 400 ASA film speed, auto white balance, and full zoom (14mm). I let the camera auto focus on the cross and read the shutter speed. Here’s what I got today at noon (the sky was pretty clear with some scattered clouds that weren’t blocking the sun when I took the outside readings):
* *3 – room with a block window facing north
*30 – outside on the north side of the house in the deep shade
*50 – on the CP shelf about 18” from the light
*60 – on west side of the house in the shade of a pillar
*80 – on the CP shelf about 14” from the light
120 – on the CP shelf about 12” from the light
160 – on the CP shelf about 10” from the light
320 – pointing the camera directly at a shelf bulb
640 – outside in the full sun
From these numbers it appears that about 10” from my bulbs the light is 25% of the full sun, which is also “Cloudy Bright”. In this trial it appears that your formula and using the light meter on my camera agree.
It's easier than that if you have a hand held light meter. My Gossen Luna-Pro F is calibrated to measure Lux when set to ASA 50. I just take a reading and get the EV (exposure value) reading and look at the chart printed on the bottom of my meter. EVs are used in photography for the Zone system made famous by Ansel Adams.
Sunny, partially cloudy, over the sun - EV 12.33 ~= 22500 Lux or cloudy bright.
My tank lights (I'm going to redo them) at the distance where my Drosera is (3-4" from lights) gives an EV of 9 ~=2800 Lux or cloudy dull.
In order to get an accurate reading you either have to take an incident reading (with an incident lens cap - use a styrofoam coffee cup if you don't have one) over the lens or a reflected reading from a standard 18% gray card.
Below is the table as calibrated for my hand held meter for a setting of ASA 50. A word of caution: just because my light meter is calibrated to use this scale it doesn't necessarily mean that this scale is applicable to any other light meter (other than another Gossen Luna-Pro F). However if your light meter can report Exposure Values then by all means experiment with this chart.
LW EV Lux ca. fc appr -5
0.016
0.02
0.025 -4
0.032
0.04
0.05 -3
0.065
0.08
0.1 -2 1.4 0.13
0.18
0.21 -1 2.8 0.26
0.33
0.4 0 5.5 0.5
0.63
0.79 1 11 1
1.26
1.6 2 22 2
2.5
3.2 3 44 4
5
6.3 4 88 8
10
12.7 5 175 16
20
25 6 350 32
40
51 7 700 65
82
103 8 1400 130
164
206 9 2800 260
328
413 10 5500 500
630
794 11 11000 1000
1260
1580 12 22000 2000
2500
3180 13 44000 4000
5040
6350 14 88000 8000
10800
12700 15 175000 16000
20100
25400 16 350000 32000
Last edited by Joseph Clemens; 01-27-2007 at 04:10 PM. Reason: Too much empty space
Grand Hotel... always the same. People come, people go. Nothing ever happens.
Not a Number – yeah it would be easier with a light meter, but since I’ve owned a number of cameras and never got a light meter I figured I would use one of my cameras. Actually, with the camera it’s pretty easy – all you have to do is measure the light at your plants, and then go outside (on a clear/bight day) and measure again, then use the table posted by Elandolf to see where you fall.
I do own a sound level meter, maybe I could use it?
I say again , not a very close approximation , remember that the formula that you use is for a pountual source of electromagnetic radiation , the lamps are not , especialy fluorescent tubs.
The calculation made like you presented will give a much higher value than the real one.
I have a digital lux meter.
Using a through the lens light meter is fine as long as you are aware that digital cameras have metering patterns (a feature introduced by Minolta in the 70's). Thus the meter has hot spots that are more sensitive or weighted to give priority readings. Many cameras have different metering pattern programs you can choose from. Thus if you are not aware of the metering pattern of you camera your readings can be skewed simply by having a hot spot on a dark area where a light area is expected. One stop difference will double or half the calculated lux figure. Take a reading through your camera then turn the camera upside down and compose the shot identically - most likely you'll get a different exposure reading depending on the mode your camera is set.
Not a Number – yeah it would be easier with a light meter, but since I’ve owned a number of cameras and never got a light meter I figured I would use one of my cameras. Actually, with the camera it’s pretty easy – all you have to do is measure the light at your plants, and then go outside (on a clear/bight day) and measure again, then use the table posted by Elandolf to see where you fall.
I do own a sound level meter, maybe I could use it?
As stated before to get around this either take an incident reading (the styrofoam coffee cup or incident reading cap over the lens) pointed at the light source from position of the subject (plant) or take a reading off a standard such as a grey card or a white card. If your camera has a spot metering mode use that. The important thing is to measure off a standard point of reference that fills the entire metering area (either the spot or entire frame).
If you're able to get a light reading using a sound meter then congratulations - you've done what Einstein and quantum physicists have not - solved the Unified Field Theory Equation.
Grand Hotel... always the same. People come, people go. Nothing ever happens.
Yeah, light and heat is the biggest issue for me. I wouldn't be able to do the maoth too work it out, but could someone twll me what the maximum heat should be inside the terrwaium? I have the Issue of just living In a place that is hot, Inside and outside. If my terrarium is 85, that's pretty "cool". I have fans thst blow but it just circulates fresh air in and old air out, its not a cooler. Then If they run for too long, I lose all humidity. Yet all I can find is a 15 minute timer.
Temp gets too high, I lose dew from my sundews and lose humidity. Too low and i dont get humidity. Tried wet sponges, frozen bottles... I dont understand how you balance It all, doesnt seem possible.
This morning when I woke up, the lights were of course off, the humidity was 70%, yet my plants didn't look too good so I just put then outside.
Think I'm gonna give up terrarium, I need an outdoor setup. But that costs a ton of money too.... Can't win. Lol.
Anyone wanna buy a t5, 4 bulb, 4 foot light? This thing just doesn't work right for me. Too big, too hot. Maybe a t8, 2 foot, 2 bulb?
What theremometer are you using? The exo-terra thermometers read really high (90+*) if water condenses in it. I put my mouth to the thermometer and suck out all the water, then look for a reading. I have noticed that the temps in the terrarium can get up to about 90* without ill effect though. How are you humidifying the terrarim? Instead of spraying, consider running an ultrasonic humidifier 24/7 and leave the top open with the lights hanging 4-6" above the terarium. I did that for a few months, and it worked really well except when the ceiling fan was running; then all the humidity left.
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