What's new
TerraForums Venus Flytrap, Nepenthes, Drosera and more talk

Register a free account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members through your own private inbox!

Calculating Light Amounts

Lots of people have been asking about their light setups so I thought I'd post how to find out exactly how much light your plants are getting. This only bothers with amounts of light, not the color temperature and index, so remember to get the right ones! This doesn't factor in everything so it is just a way to get a very close approximation

1. Measurements
a. The power of your bulbs. This is represented as P and is measure in Lumens. Lumens measure the intensity of light.
It should say on the box your lights came in how many Lumens your light emits. This measurement is taken from the surface of the bulb.
b. The distance between the light and the plants. Your plant lights are most likely going to emit light sphericaly so this distance is actually the radius of a circle. Because this circle only touches one point on the entire surface area of the plants, and you most likely have more than one light you have to deal with this by averaging the distances your lights are apart, as if the all the light is coming from one source.
c. The surface area you are lighting. A=πr²

2. The Math
Now for some math and physics. We want to find out the amount of lumens per square meter that the plants are getting. To factor in the amount of light lost from traveling to your plants you need to calculate its new intensity. For this we use the equation for intensity of electromagnetic waves, which is E=P/(4πr²). E is the intensity you want to find out. P is your total amount of Lumens added from each bulb and r is the distance (in meters) between your average 'light' and straight down to the center of the surface area of your plants. Your Intensity, E, will be in Lumens per square meter. This unit is known as luminous flux or lux for short.

Here is a chart of lux values from This website for you to compare your own to:

Outdoor Illuminance (lux)
Bright sun 50K - 100K
Hazy day 25K - 50K
Cloudy bright 10K - 25K
Cloudy dull 2K - 10K
Very dull 100 - 2K
Sunset 1 - 100
Full moon 0.01 - 0.1
Starlight 0.001 - 0.001

3. Light Loss
unnecessary, but interesting to know. To find the amount of the light lost traveling to the surface area of your plants, or change in P, you take your initial sum of Lumens and subtract the final sum of Lumens. To find your final sum of Lumens take the area of the plants you are lighting and multiply it by the intensity.

4. Mylar!
USE MYLAR AND A REFLECTOR! This will greatly increase your light amount! For each reflective surface find the distance between the light source to the center of the the reflective surface and to average center spot on your plants. Mylar reflects somewhere near 90% of light so calculate the light intensity reflected by each surface onto your plants and multiply them by .9. Now take your orignal Intensity and add each of the reflective surface's intensity's to it for a new E.

5. Light Gain
smile.gif

After finding your new intensity because of reflective surfaces, use it to find your new change in P. To do so take your new Intensity and multiply it by the area you are lighting then subtract this new number from your P initial. Negative means you gained light and positive means your still losing light but probaly a lot less than before!

EXAMPLE:
This is probaly still a little hard to understand or do so I'll take you through it by calculating the light in my new closet growshelf thats in the other thread. Hope this helps:

1. MEASUREMENTS
a. I have 4 Philips fluorescent tubes that are 2250 Lumens each. Adding them all together gives me a total of 9000 Lumens.
b. Distance from the center of these lights straight down to the surface of my growing area is about 8". 8" is about .2 meters, so my r is .2 meters.
c. The Surface area the light is going to at an 8" radius is A = π(.2m)² = .13m²


2. MATH
E = (9000 lm)/[4π(.2m)²] = (9000 lm)/(.5m²) = 18,000 lm/m² = 18,000 lux
This is equivilant to a very bright cloudy day.

3. LIGHT LOSS
P1 - P2 = (9000 lm) - [(18,000 lm/m²)(.13m²)] = (9000 lm) - (2,340 lm) = 6760 lm

4. REFLECTIONS
I don't have mylar yet but I plan on it. With 3 reflective surfaces I can measure the distance the light goes by starting at the light source and measuring the distance to each reflective surface then the distance to the spot below the light where the plants are. Surfaces 1 and 2, the left and right sides, are both 8" high. the distance from these walls to the center spot is 19.5". Drawing my ray of light gives me two symetrical triangles that I need to find the length of hypotenuse's for. Using Pythagoreans theory of A² + B² = C² and solving for C (the hypotnuse) and then doubling it will give me a distance, r. 2C = 2[(A² + B²)^(1/2)] = r. Converting my inches to meters and plugging them in I get [(.5m)² + (.1)²]^(1/2) = (.25m² + .01m²)^(1/2) = .26m²^(1/2) = .5m. My third surface, the back, is 8" high and 9" away from the center. Repeating the triangle process I get .3m

5. LIGHT GAIN
Starting with the two surfaces where the light bounces at the plants from a distance of r = .5m I plug this into the intensity equation. E1&2 = (9000 lm)/[4π(.5m)²] = (9000 lm)/(3.14m²) = 2866.24 lux. Then I do the last surface E3 = (9000 lm)/[4π(.3m)²] = (9000 lm)/(1.13m²) = 7964 lux. Adding all of the light intensitys gives us the final total. E = Eo + E1 + E2 + E3 = (18,000 lux) + (2866.24 lux) + (2866.24 lux) + (7964 lux) = 31968 lux. My cloudy bright day just went to an slightly hazy sunny day.

To see how much light was lost with the reflective surfaces I subtract the new P final from P initial. P = P1 - P2 = (9000 lm) - [(31968 lux)(.13m²)] = (9,000 lm) - (4120.5 lm) = 3879.5 lm

as you can see the light loss for reflective surfaces is half of what it would be with no reflective surfaces. When you add a reflector right next to the bulb you can do some serious damage
smilie4.gif




Hope this helps, please correct any errors if you can because I know there are much more accurate and complex ways to do it! What are your guys' light conditions?
 
*faints and convulses* (in weak voice)too much math! cant take it all in...i...am supposed to be on spring break......lol thanks for all of this! maby this should be stickyed up!
alex
 
You might want to do a simple version like how you did here
That was pretty easy to follow for most ppl without the b = L/4(pi)r^2 things. Takes a considerable time to figure it out. But anyway, something like this should be stickied, good job for initiating it.
smile.gif
 
complicate to me but i read it all!!
smile.gif
 
that was pi? it didnt look like pie....

Thanks though!
Cheers
 
pi is 3.1416314163141631416314163141631416314614163141631416314163141631416314163146141631416314
163141631416314163141631461416314163141631416314163141631416314614163141631416314163141631
416314163146141631416314163141631416314163141631461416314163141631416314163141631416314614
163141631416314163141631416314163146141631416314163141631416314164163141631416314163146141
631416314163141631416314163141631461416314163141631416314163141631416314614163141631416314
164163141631416314163141631416314614163141631416314163141631416314163146..... i was going to put a entire page of this but i tink it would b a bad joke XDDDD am i right?, well answering the question if u say pi the symbol like ñ¬ or somering i tink is a math stuff, i read it from a book a yeras ago and i tink is infynyte...
biggrin.gif
 
Thanks for the information! This will come in handy for some people. Call me lazy, but I ordered a light meter to do the work for me. LOL
 
hear are the first 500 digets of pi

3.
14159 26535 89793 23846 26433 83279 50288 41971 69399 37510
58209 74944 59230 78164 06286 20899 86280 34825 34211 70679
82148 08651 32823 06647 09384 46095 50582 23172 53594 08128
48111 74502 84102 70193 85211 05559 64462 29489 54930 38196
44288 10975 66593 34461 28475 64823 37867 83165 27120 19091
45648 56692 34603 48610 45432 66482 13393 60726 02491 41273
72458 70066 06315 58817 48815 20920 96282 92540 91715 36436
78925 90360 01133 05305 48820 46652 13841 46951 94151 16094
33057 27036 57595 91953 09218 61173 81932 61179 31051 18548
07446 23799 62749 56735 18857 52724 89122 79381 83011 94912
98336 73362 44065 66430 86021 39494 63952 24737 19070 21798
60943 70277 05392 17176 29317 67523 84674 81846 76694 05132
00056 81271 45263 56082 77857 71342 75778 96091 73637 17872
14684 40901 22495 34301 46549 58537 10507 92279 68925 89235
42019 95611 21290 21960 86403 44181 59813 62977 47713 09960
51870 72113 49999 99837 29780 49951 05973 17328 16096 31859
50244 59455 34690 83026 42522 30825 33446 85035 26193 11881
71010 00313 78387 52886 58753 32083 81420 61717 76691 47303
59825 34904 28755 46873 11595 62863 88235 37875 93751 95778
18577 80532 17122 68066 13001 92787 66111 95909 21642 01989

38095 25720 10654 85863 27886 59361 53381 82796 82303 01952
03530 18529 68995 77362 25994 13891 24972 17752 83479 13151
55748 57242 45415 06959 50829 53311 68617 27855 88907 50983
81754 63746 49393 19255 06040 09277 01671 13900 98488 24012
85836 16035 63707 66010 47101 81942 95559 61989 46767 83744
94482 55379 77472 68471 04047 53464 62080 46684 25906 94912
93313 67702 89891 52104 75216 20569 66024 05803 81501 93511
25338 24300 35587 64024 74964 73263 91419 92726 04269 92279
67823 54781 63600 93417 21641 21992 45863 15030 28618 29745
55706 74983 85054 94588 58692 69956 90927 21079 75093 02955
32116 53449 87202 75596 02364 80665 49911 98818 34797 75356
63698 07426 54252 78625 51818 41757 46728 90977 77279 38000
81647 06001 61452 49192 17321 72147 72350 14144 19735 68548
16136 11573 52552 13347 57418 49468 43852 33239 07394 14333
45477 62416 86251 89835 69485 56209 92192 22184 27255 02542
56887 67179 04946 01653 46680 49886 27232 79178 60857 84383
82796 79766 81454 10095 38837 86360 95068 00642 25125 20511
73929 84896 08412 84886 26945 60424 19652 85022 21066 11863
06744 27862 20391 94945 04712 37137 86960 95636 43719 17287
46776 46575 73962 41389 08658 32645 99581 33904 78027 59009

94657 64078 95126 94683 98352 59570 98258 22620 52248 94077
26719 47826 84826 01476 99090 26401 36394 43745 53050 68203
49625 24517 49399 65143 14298 09190 65925 09372 21696 46151
57098 58387 41059 78859 59772 97549 89301 61753 92846 81382
68683 86894 27741 55991 85592 52459 53959 43104 99725 24680
84598 72736 44695 84865 38367 36222 62609 91246 08051 24388
43904 51244 13654 97627 80797 71569 14359 97700 12961 60894
41694 86855 58484 06353 42207 22258 28488 64815 84560 28506
01684 27394 52267 46767 88952 52138 52254 99546 66727 82398
64565 96116 35488 62305 77456 49803 55936 34568 17432 41125
15076 06947 94510 96596 09402 52288 79710 89314 56691 36867
22874 89405 60101 50330 86179 28680 92087 47609 17824 93858
90097 14909 67598 52613 65549 78189 31297 84821 68299 89487
22658 80485 75640 14270 47755 51323 79641 45152 37462 34364
54285 84447 95265 86782 10511 41354 73573 95231 13427 16610
21359 69536 23144 29524 84937 18711 01457 65403 59027 99344
03742 00731 05785 39062 19838 74478 08478 48968 33214 45713
86875 19435 06430 21845 31910 48481 00537 06146 80674 91927
81911 97939 95206 14196 63428 75444 06437 45123 71819 21799
98391 01591 95618 14675 14269 12397 48940 90718 64942 31961

56794 52080 95146 55022 52316 03881 93014 20937 62137 85595
66389 37787 08303 90697 92077 34672 21825 62599 66150 14215
03068 03844 77345 49202 60541 46659 25201 49744 28507 32518
66600 21324 34088 19071 04863 31734 64965 14539 05796 26856
10055 08106 65879 69981 63574 73638 40525 71459 10289 70641
40110 97120 62804 39039 75951 56771 57700 42033 78699 36007
23055 87631 76359 42187 31251 47120 53292 81918 26186 12586
73215 79198 41484 88291 64470 60957 52706 95722 09175 67116
72291 09816 90915 28017 35067 12748 58322 28718 35209 35396
57251 21083 57915 13698 82091 44421 00675 10334 67110 31412
67111 36990 86585 16398 31501 97016 51511 68517 14376 57618
35155 65088 49099 89859 98238 73455 28331 63550 76479 18535
89322 61854 89632 13293 30898 57064 20467 52590 70915 48141
65498 59461 63718 02709 81994 30992 44889 57571 28289 05923
23326 09729 97120 84433 57326 54893 82391 19325 97463 66730
58360 41428 13883 03203 82490 37589 85243 74417 02913 27656
18093 77344 40307 07469 21120 19130 20330 38019 76211 01100
44929 32151 60842 44485 96376 69838 95228 68478 31235 52658
21314 49576 85726 24334 41893 03968 64262 43410 77322 69780
28073 18915 44110 10446 82325 27162 01052 65227 21116 60396

66557 30925 47110 55785 37634 66820 65310 98965 26918 62056
47693 12570 58635 66201 85581 00729 36065 98764 86117 91045
33488 50346 11365 76867 53249 44166 80396 26579 78771 85560
84552 96541 26654 08530 61434 44318 58676 97514 56614 06800
70023 78776 59134 40171 27494 70420 56223 05389 94561 31407
11270 00407 85473 32699 39081 45466 46458 80797 27082 66830
63432 85878 56983 05235 80893 30657 57406 79545 71637 75254
20211 49557 61581 40025 01262 28594 13021 64715 50979 25923
09907 96547 37612 55176 56751 35751 78296 66454 77917 45011
29961 48903 04639 94713 29621 07340 43751 89573 59614 58901
93897 13111 79042 97828 56475 03203 19869 15140 28708 08599
04801 09412 14722 13179 47647 77262 24142 54854 54033 21571
85306 14228 81375 85043 06332 17518 29798 66223 71721 59160
77166 92547 48738 98665 49494 50114 65406 28433 66393 79003
97692 65672 14638 53067 36096 57120 91807 63832 71664 16274
88880 07869 25602 90228 47210 40317 21186 08204 19000 42296
61711 96377 92133 75751 14959 50156 60496 31862 94726 54736
42523 08177 03675 15906 73502 35072 83540 56704 03867 43513
62222 47715 89150 49530 98444 89333 09634 08780 76932 59939
78054 19341 44737 74418 42631 29860 80998 88687 41326 04721

It does not repeat its self it is never ending... Highest number counted is like 85,000 digits remberd..

Cheers
 
Wow you sure have a good memory Nep_ak!
smile_n_32.gif


I think some types of cameras can be used as a light meter as well, but don't know the procedure.
 
  • #10
I agree that a light meter would be by far the best way to find out, because this method does not take into account 100% correctly the reflection, light loss factor, lamp lumen maintenance factor, luminaire maintenance factor, room surface maintenance factor, utilisation factor, light output ratio of luminaire, flux distribution of luminaire, room proportions, and spacing to height ratio.

Later on in my free time I will try to make little ammendments and an extension to the article of how to do it with all these factors. For now I would stick with my sort of inaccurate average way to do it or consult this article that requires things like calling the actual light company to find the depreciation rate of lumens for specific lights and etc.
 
  • #11
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.
 
  • #12
[b said:
Quote[/b] ]This doesn't factor in everything so it is just a way to get a very close approximation

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.
 
  • #13
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.
 
  • #14
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.

<table border="1"><tbody><tr valign="bottom"><td align="left">LW EV</td><td align="left">Lux ca.</td><td align="left">fc appr</td></tr><tr valign="bottom"><td align="right">-5</td><td align="right">
</td><td align="right">0.016</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">0.02</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">0.025</td></tr><tr valign="bottom"><td align="right">-4</td><td align="right">
</td><td align="right">0.032</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">0.04</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">0.05</td></tr><tr valign="bottom"><td align="right">-3</td><td align="right">
</td><td align="right">0.065</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">0.08</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">0.1</td></tr><tr valign="bottom"><td align="right">-2</td><td align="right">1.4</td><td align="right">0.13</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">0.18</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">0.21</td></tr><tr valign="bottom"><td align="right">-1</td><td align="right">2.8</td><td align="right">0.26</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">0.33</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">0.4</td></tr><tr valign="bottom"><td align="right">0</td><td align="right">5.5</td><td align="right">0.5</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">0.63</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">0.79</td></tr><tr valign="bottom"><td align="right">1</td><td align="right">11</td><td align="right">1</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">1.26</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">1.6</td></tr><tr valign="bottom"><td align="right">2</td><td align="right">22</td><td align="right">2</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">2.5</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">3.2</td></tr><tr valign="bottom"><td align="right">3</td><td align="right">44</td><td align="right">4</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">5</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">6.3</td></tr><tr valign="bottom"><td align="right">4</td><td align="right">88</td><td align="right">8</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">10</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">12.7</td></tr><tr valign="bottom"><td align="right">5</td><td align="right">175</td><td align="right">16</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">20</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">25</td></tr><tr valign="bottom"><td align="right">6</td><td align="right">350</td><td align="right">32</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">40</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">51</td></tr><tr valign="bottom"><td align="right">7</td><td align="right">700</td><td align="right">65</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">82</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">103</td></tr><tr valign="bottom"><td align="right">8</td><td align="right">1400</td><td align="right">130</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">164</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">206</td></tr><tr valign="bottom"><td align="right">9</td><td align="right">2800</td><td align="right">260</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">328</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">413</td></tr><tr valign="bottom"><td align="right">10</td><td align="right">5500</td><td align="right">500</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">630</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">794</td></tr><tr valign="bottom"><td align="right">11</td><td align="right">11000</td><td align="right">1000</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">1260</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">1580</td></tr><tr valign="bottom"><td align="right">12</td><td align="right">22000</td><td align="right">2000</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">2500</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">3180</td></tr><tr valign="bottom"><td align="right">13</td><td align="right">44000</td><td align="right">4000</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">5040</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">6350</td></tr><tr valign="bottom"><td align="right">14</td><td align="right">88000</td><td align="right">8000</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">10800</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">12700</td></tr><tr valign="bottom"><td align="right">15</td><td align="right">175000</td><td align="right">16000</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">20100</td></tr><tr valign="bottom"><td align="right">
</td><td align="right">
</td><td align="right">25400</td></tr><tr valign="bottom"><td align="right">16</td><td align="right">350000</td><td align="right">32000</td></tr></tbody></table>
 
Last edited by a moderator:
  • #15
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?
wink.gif.gif
 
  • #16
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.
 
  • #17
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?
wink.gif.gif

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.

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).

:hail: 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.
 
  • #18
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?
 
  • #19
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.
 
Back
Top