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Thread: Light

  1. #1

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    Light

    Lets talk light for a minute.
    Now light coming from a globe isnt dependant on the power is uses ie a 25W T5 isnt giving out 25Watts of light this is meaningless as light is measured by the amount of photons (packets of light) per amount of time another measure is lumans output

    This equivalent part is what gets me 1Watt isnt the light its putting out its the power its consuming.
    most T4 lights are approximatly 60-70 lumans per watt (some new ones up to 90lumans/watt)
    most T5 are around 70-80
    CFL are around 50-65 but are cheap usually in comparison
    MH are aroudd 60-100ish (higher wattagaes are more efficient but cost more to run)
    LED are 110-136lumans per watt (these have their own draw backs aswell)

    Geneal rule for scrubbing
    0.5 actual (not equivalent) fluorescent watts per gallon MINIMUM.
    1.0 actual (not equivalent) fluorescent watts per gallon for HIGH filtering.
    now watts is what the light unit uses to gennerate its light output which for light is lumans (packets of light per unit time) which is what we are interested in.

    So in the guide it says not equivalent fluroesscent watt and as far as i can tell you based it on T5 lighting and that you cant have too much light essentially but cost of running lights and effective scrubbing are two very different things.
    Therefore assuming 70-80lumans per watt we are using T5's as the SM100 puts out 7-8000lumans as its 100watt total. (assuming good reflectors so that close to 100% of the light emitted is directed to the screen)

    This is for high filtering (1W per square inch)
    The screen is 200cubic inches so essentially we have 40 lumans per square inch of screen.
    2X100 square inches = 200 inches^2 total
    8000/200 = 40 lumans/square inch.
    so 40 lumans per squareinch of screen has been found to be high level of scrubbing by your design which speaks for itself in effectivness.

    Now lets look at it from a tank volume point of view. tank volume is 100 gallons so thats an easy 70-80 lumans per gallon for good filtering

    common sizes of tank and light needs
    28 gal needs 2000lumans at 1.5inches away form screen
    50 gal needs 3500 lumans at 1.5inches
    100gal needs 7000 lumans at 1.5inches.
    150gal needs 10500 lumans at 1.5 inches .
    500gal needs 35,000 lumans at 1.5inches.

    Lets look at Lux or light power per unit area
    Now lux (SI) or footcandle (IMperial) is the light power per unit area.
    40 lumans on 1 square inch (0.000625m^2) is 64,000 lux (close to 6000 foot candle) as a rough guide to the amount of light you should be aiming for for good filtering. As a guide direct sulight starts at 32,000 lux and goes up to 130,000lux so the light needed is around 1/2 the power of the sun ( this doesnt include infared light which is the power of the sun that we feel its the sun in light intensity)

    Lux depends on the area we are illuminating. Decent reflectors are a way to focus the light but they can only do so much so placing the light source close to the screen is a good way to increase effective irridance. look at reflectors that throw the light to the entire screen surface while being as close as possible to the screen to give uniform light distribution. but being in this 1-2inch range is where the aquerium reflectors ad DIY reflectors are going to be able to throw most of the light effectivly.

    I hope this helps a little to the knowledge of light needs and hope it helps future development of lighting or design.

  2. #2

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    Re: Light

    Very good analysis.

    And I like the last part about emphasizing Lux.
    That is really the critical scientific measurement to use : Lux value at the screen.
    Everything else has way too many variables and can be almost meaningless.

    Unfortunately, the math does not match what I measure. And I think the problem is that
    your assumption of near 100% is pretty far off.
    I checked your calculations quickly, and it does seem that a T5 at one inch would be 64,000 lux.
    From memory (I need to check again), my measurement was something like 25,000
    That was with the best available refector, and an over-driving icecap ballast.
    But it was with a 1/8" acrylic shield. Reflectors are far from perfect. Specs are not always what they say.

    The second factor, which is excruciatingly hard to quantify, is spectrum.
    Algae use a completely different spectrum than we, or our normal light meters, use.
    If you match that, you can get a huge increase in efficiency.
    Incidentally what I really hope to achieve with LEDs.

    I also want to mention the value of optics.
    With a point source of light, the lux drops as the cube of the distance.
    With a linear source of light, it drops as the square.
    But a focused beam (laser) drops barely at all.
    Basically, with a cheap CFL, no reflector, if you move it from 1" away to 4" away, the lux drops 1/64.
    But with a focused beam, say an LED with a 30-deg optic on it, the difference is almost nothing.

    Maybe someone can measure the lux of our gold-standard SM100, right at the screen.

  3. #3
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    Re: Light

    Come over and measure

  4. #4

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    Re: Light

    Thanks for some solid data on the lux findings you are getting.

    There are some funny things with lux in that it is a measure of the light the human eye precieves in that it is weighted toward the yellow/green part of the spectrum. a PAR metre is weighted for what plants see. they are distinctly different as can be seen below in the picture


    A is what the PAR meter measures and is the wavelegths needed by plants(coral, photosynthesis etc) to provide food for themselves.
    B is what the human eye see's and lumans is weighted the same as LUX (what the eye see's)

    That is why LED for instance give us very good PAR regulated output now and thus needs to output more light that we are not sensitive too to get similar lumans to CFL since CFL have alot more green/yellow light emitted then LED's.

    LED's at 100lumans would give out more PAR then T5 fluro's at 100 lumans with everything else being equal like LUX etc because of the weighting oof the light components. this is why it is easier to make high lumans yellow light as that what its measured on. and why you dont see lumans values for blue and red LED's etc as the weighting is so low on those colours.

    Polycarbonate is very good at transmitting light only a few %loss similar with acrylic being a % or more loss.

    Algae as far as i can tell form what little data is available is that it makes use of the light spectrum that most plants dont use ie the 500-600nm green yellow part of the spectrum and one of the biggest reason for the push to LED for Display tanks is that is supresses the liklyhood of algae growth as it limits those wavelengths.

    What is needed is to find out what type of algae we are actually growing im assuming just the nice green hair algae and then do some experiments on that with different spectrum weighted lights.

    This could give a massive increase in efficiency. i have seen somewhere possible SM said that 3200K globes work the best. If you can remember the brand of these globes SM or whoever said it i'll look up some output tables and do some analysis.

    last thing is the algae that grows is green hair algae im assuming?

  5. #5
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    Re: Light

    Green hair is best, but other types work too.

  6. #6

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    Re: Light

    That "A" curve for what algae needs looks fairly incorrect. Where did you get that?
    It seems far too high in the center green regions.

    Some good threads with a lot of data (biased, since I started a few)
    viewtopic.php?f=3&t=435
    viewtopic.php?f=3&t=560
    viewtopic.php?f=3&t=561

    Several of us have been experimenting a lot with different LED types.
    Still no real agreement.
    Seem like a combo of deep red + blue + some warm-white is good though.

  7. #7

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    Re: Light

    The curve isnt for algae just a comparison from light plants need vs what the human eye sees (from which lux and lumans are deterimened) i believe that the A is just a averaged result form all the photon aceptors in plants (chlorophyll etc etc).

    Upon furthur looking it seams as if all green algaes make their food and thus photosynthesise via chlorophyll and thus the non abosrption of green light which gives it its green colour.

    the spectrums of absorption for chlorophyll A and B are as follows

    chlorophyll a has approximate absorbance maxima of 430 nm and 662 nm, while chlorophyll b has approximate maxima of 453 nm and 642 nm

    So if we can provide light in the 400-500nm as well as 620-680nm region it should be able to get all of its light required. using these two regions will cause the algae to grow the best. Releative equal amounts of these two bands will give the best growth rate. While not so crash hot for DT lighting it would promote good growth.

    Spectral distribution.
    A far as i can tell form Cree's specs the XP-G that is common for LED lighting has some of the peaks covered but to reach the 450-500nm range some royal blues and blues are need to beef up that part of the spectrum and there is no 630+nm led that cree make to boost that part of the spectrum so that mite be difficult but the rest seams to be very well covered. the fluroessence of chlorophyll a is about 670 so soe of the light it acepts it mite be able to break down and make it useful.

    grow lights made for hydroponics use a fair amount of red LED's mixed with blues to make the plants grow the best. i need to look at some more LED manufactures to see if any make long wavelength LEDs though

  8. #8

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    Re: Light

    Hm reading through 22 pages of that LED thread shows some very good advancement and data found out.

    have you increased your flow to your led screen yet rygh and has it helped with getting your screen green as opposed to yellow?
    like you said there are ppl using twice the power in LED's that you are using and they are getting green so SM's assumption of flow mite be the crutial thing. afterall flow in a natural reef is 10 fold what we replicate in a tank so maybe that really is the key.

    the deep red plus blue spread is looking good. even if you are producing yellow algae it still seams to be filtering very well.

  9. #9

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    Re: Light

    The trick to making it green instead of yellow was to reduce the lighting.
    (Also advice by SM)
    Lighting is at 12 hours/day, and there are some duct-tape strips for further reduction.
    Increasing flow had no effect.

    The 30W of LEDs was just too powerful. Cool!

    It is doing fairly well now as the only filter in the system. The skimmer and RDSB have been removed. Extra feeding as well.

    The problem I have is that it cannot really out-compete the purple bubble algae in the main tank.
    Really seems to be a function of the horizontal design.
    So I am building a vertical version. Also needed for a future larger tank.

  10. #10

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    Re: Light

    Manufacturers make any wave length you want. The problem is cost at that point once you wander out of the "main stream" All mainstream blues are going to be between 450-470 which means the blue spike on the white LED's from that manufacturer are also going to be in the same spot since white LED's are blue LED's modified with phosphors.

    I've used just warm white 3200k. If you've looked at the graphs Cree has up you can see the spectrum output of them..and all LED's output is roughly the same per given Kelvin rating.I too was looking at and thinking about trying to hit all these chlorophyl absorbtion peaks..but after getting results with the 1 watt warm white only I just dropped it. Trust me I spent weeks pouring over graphs and information on algae its sick.

    They reasonably aproximate the output of a low kelvin CFL.I used 1 watt LED's to get the light spread more evenly and at the right intensity. You can also get cheap 1w LED's off ebay that are like 70lumens per watt. roughly 50-70 cents each if you can deal with LED's that are not star mounted. about $1.50-$2 each if they are star mounted. You can buy either in lots of 10-20-50-100 etc and save a great deal of money.

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