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Ageing T8's

Discussion in 'Lighting' started by scottward, Mar 9, 2010.

  1. Philosophos

    Philosophos Lifetime Charter Member
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    Maybe you can clear me up on this one, but I thought CRI had nothing to do with PAR, and little to do with aesthetic given that we're not always looking for full rendering?
     
  2. SuperColey1

    SuperColey1 Guru Class Expert

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    I have to state I am by no means sure of this as I am not an expert in this field but I am under the assumption that a like for like tube in different K gives different Lumens and different PAR, meaning that a red light gives less than a white light and white les than blue etc.

    If so then if a tube is 99% accurate to 5000K and that 5000K gives say 150Par at source then I would assume a '5000K' tube that is 50% accurate may be within the region of 4000 - 6000K. As we know that 4000K is pink and that we are assuming that pink gives less PAR than white and blue then all of a sudden the CRI does come into play because you bought a tube expecting 5000K and 150 PAR when the actual may be that it is 4000K/pink giving 120Par or 6000K/green giving 180Par (These are assumptions and made up figures :) ) therefore if we can get a high CRI then the colour should be more accurate when you get the lamp and also not wander from the starting point as quickly.

    Now I could be wrong and it could be that it is Lumens (not the altered figures for the human eye but actual) that drop of in the reds and gain in the blues where PAR stays the same!!! who knows :) It may be that the CRI is also a human interpretation of colour where the actual light (PAR/PUR) remains the same :)

    AC
     
  3. shoggoth43

    shoggoth43 Lifetime Charter Member
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    CRI is Color Rendering Index? One would think they'd correlate with PAR but I don't know if that's true. I'm also not sure if the 50% means the color could be off like you suggest. It could just be that the phosphors in use leave "gaps" in the spectrum. i.e. Reds/greens/blues are fine, the white balance is good, but there's a distinct lack of purple or some such like that. Otherwise everything is spot on. I don't really know, but that's always been my assumption on that given how they tend to show the spectrum charts on some of these lamps. Then again, maybe what I thought it was ends up being your concept anyway since if you have enough gaps in the lighting the color would look like it shifted anyway.

    -
    S



     
  4. Brian20

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    In my experience, more CRI more overall quality. You see the plants and fishes with more natural color, it is like sun light. Low CRI is more like the red or blue tubes that "tint" the water that color.
     
  5. nipat

    nipat Guru Class Expert

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    No, a low CRI bulb can give pure white (doesn't tint water) to human eyes too.
    But its spectrum is unlike sunlight at that K (generally lacking some ranges as
    S said). So objects under that low CRI light will have more chance to look unlike
    under sunlight at that K. That's why high CRI lights are needed for color critical jobs.
     
  6. Brian20

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    In other words, low CRI have low % of some colors and high % in other and high CRI have high % in al colors that make withe light. You say CRI light are needed for color, so high CRI is the best for colors in the planted tank.
     
  7. Brian20

    Brian20 Guest

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    I need to check that place sell to PR?
     
  8. Philosophos

    Philosophos Lifetime Charter Member
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    I did a bit of reading. CRI is completely based around matching sunlight, and it's subjective. Wikipedia even has a controversy section on the article because of just that.

    I'd say that high CRI isn't always favorable. Do you really want to encourage yellows and browns to make your imperfections pop? Do you want full greens when much of the tank is already bright green, but reds are scarce? I think it's all about aesthetic. Understanding rendering and color theory is important to a good show tank, but I don't think a CRI of 100 is always the goal.
     
  9. barbarossa4122

    barbarossa4122 Guru Class Expert

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    I have electronic ballasts and Giesemann bulbs. I should be OK for 2 yrs, I hope.
     
  10. csmith

    csmith Guest

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    I was always under the impression that anything other than T-12s (namely T-5s) were fine until they burn out because they don't lose enough to be useless before they go. Is this not true?
     
  11. Brian20

    Brian20 Guest

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    well in my experience high CRI is better. yeah, maybe CRI 100 not is good idea, still the aquarium looks better in CRI 90 for example than CRI 69. Still almost all tubes Daylight are CRI 80 and up. I always looks for the more CRI tube and more lumen. I currently use a mix of tubes, ones with CRI 90 and other with lower CRI. THe CRI 90 (or more I think) are daylight.
     
  12. SuperColey1

    SuperColey1 Guru Class Expert

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    Not true no. The replace every 6-12 months is a myth but after a certain time the tubes will dminish. Like I posted earlier. tests were showing 5% loss after 40% of life. I use a conservative lifetime of 20000 hours to reach a 40% figure of nearly 3 years. Many tubes quote 36000 hours as their lifetime therefore 40% of this would be nearly 5 years.

    The lifetime quote is from when it is first turned on until the tube burns out. That may mean it runs for the final year of its life at a very faint glow but not quite fully burnt out :)

    Therefore between 3 and 5 years the amount should be minimal if running on programmed electronic ballasts.

    Its not that the tubes are T12 that makes them burn out quicker than T5. It is because they are all run off magnetic but I dare say there are electronic ballasts available for T12, just hard to find. T12, T8, T5 will all last as long. technology moves for everything and a T12 made today will be better than a T12 made in the 70s due to advances.

    AC
     
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