User Tag List

Informational! Informational!:  0
Likes Likes:  0
Page 1 of 3 123 LastLast
Results 1 to 8 of 19

Thread: Calculating Light Amounts

  1. #1

    Join Date
    Jul 2005
    Location
    Beaverton, OR
    Posts
    83
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    Unhappy

    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=πr

    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/(4πr). 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
    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) = .13m


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

    3. LIGHT LOSS
    P1 - P2 = (9000 lm) - [(18,000 lm/m)(.13m)] = (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 A + B = C and solving for C (the hypotnuse) and then doubling it will give me a distance, r. 2C = 2[(A + B)^(1/2)] = r. Converting my inches to meters and plugging them in I get [(.5m) + (.1)]^(1/2) = (.25m + .01m)^(1/2) = .26m^(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)] = (9000 lm)/(3.14m) = 2866.24 lux. Then I do the last surface E3 = (9000 lm)/[4π(.3m)] = (9000 lm)/(1.13m) = 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)(.13m)] = (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



    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?

  2. #2
    Always a newbie glider14's Avatar
    Join Date
    Oct 2005
    Location
    Louisville, Kentucky
    Posts
    3,956
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    *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
    Everything is explainable. The seemingly unexplainable is but a result of our insufficient knowledge.- Hans Brewer

  3. #3

    Join Date
    Nov 2003
    Location
    Singapore
    Posts
    1,453
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    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.

  4. #4

    Join Date
    Mar 2006
    Location
    mexico
    Posts
    99
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    complicate to me but i read it all!!

  5. #5
    nepenthes_ak's Avatar
    Join Date
    Mar 2006
    Location
    Spring Feild Ohio
    Posts
    3,116
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    that was pi? it didnt look like pie....

    Thanks though!
    Cheers

  6. #6

    Join Date
    Mar 2006
    Location
    mexico
    Posts
    99
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    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 or somering i tink is a math stuff, i read it from a book a yeras ago and i tink is infynyte...

  7. #7
    Cardiac Nurse JB_OrchidGuy's Avatar
    Join Date
    Apr 2005
    Location
    SC
    Posts
    3,818
    Mentioned
    2 Post(s)
    Tagged
    0 Thread(s)
    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
    JB
    Friend me on facebook with JB_orchidguy@yahoo.com.
    Growlist Updated 05/08/13

  8. #8
    nepenthes_ak's Avatar
    Join Date
    Mar 2006
    Location
    Spring Feild Ohio
    Posts
    3,116
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    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

Page 1 of 3 123 LastLast

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •