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Thread: kelvin rating vs colour spectrum ANSWERED!

  1. #46
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    There is a lot of good info here & without reading it all, I think that like I did, most people are going to read the 1st post 1st, then a few more before they draw a conclusion.

    Based on that, I think there are at least 2 points that should be edited from the 1st post.

    1. Kelvin rating is NOT negligible. If you believe that then get a $2 coles tube & see what happens. Plants need UV, heat & light to survive. The kelvin rating, as has been established is a light-heat rating & is VERY important to plant life. I have an 18,000k T8 tube & it's great for plant growth, but I had to lift it 70mm from the tank as it was burning my plants.

    2. Heating metal is not a good example. I have a lot of experience in metal trades & welding etc & I'll guarantee that when heated, steel particularly goes red, then orange then just before melting point turns blindingly white. The only time it goes blue is when it's cooled.

    I've got one for you. Can someone explain why my 18,000k T8 tube has a yellow/pinkish tone to it, definitley not blue? It is defenitely 18,000k. I spoke to someone at a shop about it & they had done the research on it & had a theory pertaining to the properties of the glass but it's beyond me.
    Last edited by Sharky1; 02-07-09 at 03:55 PM.

  2. #47
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    I think it's more that kelvin is a perceptually based rating, and so not always an accurate measurement of the PAR of a particular light source.

    "$2 coles tubes" can be various kelvin ratings and I'm using them now.
    Last edited by killimike; 03-07-09 at 09:23 AM.

  3. #48
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    Quote Originally Posted by Sharky1 View Post
    1. Kelvin rating is NOT negligible. If you believe that then get a $2 coles tube & see what happens. Plants need UV, heat & light to survive. The kelvin rating, as has been established is a light-heat rating & is VERY important to plant life. I have an 18,000k T8 tube & it's great for plant growth, but I had to lift it 70mm from the tank as it was burning my plants.
    Sharky, i think you're a bit confused here. Kelvin rating as a measure of colour temperature has nothing to do with kelvin as a measure of heat temperature.

    Without getting too technical, Kelvin in heat temperature parameters is the same unit size as degrees celcius + 273. so if you really did have a 18,000 kelvin (in terms of heat) tube, it would be 17,726 degrees celcius. to put this into perspective, the surface of the sun is only 6,000 kelvin. so your aquarium would probably become the next chernobyl!


    Quote Originally Posted by Sharky1 View Post
    2. Heating metal is not a good example. I have a lot of experience in metal trades & welding etc & I'll guarantee that when heated, steel particularly goes red, then orange then just before melting point turns blindingly white. The only time it goes blue is when it's cooled.
    again without getting too scientific, the kelvin colour temp is based on the colour emitted by a black body at various temperatures. so basically it's an indication of COLOUR, not HEAT.
    when you say your steel turns blue, that's the colour of the steel once cooled, not the colour of the heat emitted. as you indicated, heating makes it go through the colours of red orange and white and cools down the same way. blue in your example is the colour of the steel itself. in terms of black body, it is a theoretical concept. no such thing exists, but basically what a black body is, is something that reflects no light and therefore is absolute black. this is different to steel which actually has colour.

    hope that clears up your doubts.
    kelvin as in terms of colour temp does not matter. that's why your 18,000K tube grows plant just as well as someone else's 6,500K tube
    [sigpic][/sigpic]
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  4. #49
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    Oh rightio. I've obviously misunderstood explanations I've had previously.

    What you say makes sense. So what is it in a tube that gives plants what they need to grow?

    I know they need, UV light & heat (along with water, nutrients & CO2) & different species like different amounts of each but what would make you chose a 10,000k & a 6500k tube combo over a single 15,000k or 18,000k tube (besides aesthetics)? If it's negligible then what are the other varying factors that matter?
    Last edited by Sharky1; 03-07-09 at 10:32 AM.

  5. #50
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    thanks for the explanation.

  6. #51
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    Something I've wondered: Would a bulb with a higher CRI always grow plants better?

    Say for example I have a bulb with a CRI of 90 and one with a CRI of 80, however the one with a CRI of 80 has larger peaks in the blue and red regions of the spectrum. Which would you expect to perform better?

  7. #52
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    Sorry posted then realized I'm 3 years to late for the question.
    cheers Jim
    Last edited by jimbshrimps; 27-01-11 at 08:38 PM.
    The speller/writer from hell,
    Sorry I suffer spelling and grammar difficulties, Please be patient. "THANKS"

  8. #53
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    SA ADEL
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    So the question remains, what is a light brand / link to buy thats best available and easy to get in Aus?
    The ultimate measure of a man is not where he stands in moments of comfort and convenience, but where he stands at times of challenge and controversy.
    Martin Luther King, Jr.

  9. #54

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    I agree that only different light color(wave length) has effect on plant's grow. All factories who make led grow light design led light pattern to completely red, blue or pink(red and blue). A study from Japan(i forgot what it is called) also proved this. Maybe Kelvin is related to the light's lifespan or efficiency i guess. as i know heat dissipation is a great problem for led product.

  10. #55

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    Just reading comments over the past 3 years of this thread. Some really great articles posted on page 1 of this thread.

    Great and an informative read !!

  11. Default

    Could you share the data from your underwater spectroradiometer? We are considering building a LED light source for aquariums.

  12. Default

    Kelvins are a unit of measure of CCT - correlated color temperature - see http://www.lrc.rpi.edu/programs/nlpi.../whatisCCT.asp

    It has nothing to do with the lifespan or efficiency of a lifespan.

    Heat management is very important in designing a LED product because the hotter you run an LED the quicker it will fail. We design our LED products to run very cool. There are other areas of concern that need to be addressed if your product is going to live up to the promise of ultra high efficiency and extreme long life.

  13. Default

    CCT as expressed in Kelvins is not about heating metal. It is an idealized black body temperature that produces white light when heated to a certain temperature Kelvin.

    Don't go nuts over Kelvin temperature. Plants evolved under sunlight. The CCT of sunlight continually varies because of the passage of the light through the atmosphere. It has a much lower CCT at sundown and sunset and much higher at noon. The amount of moisture in the air has a significant effect also. Clouds also effect it.

    Some examples of CCTs can be found at http://www.schorsch.com/en/kbase/glossary/cct.html

  14. Default Different Plants have different lighting needs

    This seems obvious but this factor may cause some confusion to neophytes to the hobby. Choosing plants that can be found in the same microclimate should simplify the lighting needs.

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