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Light, wavelength and optical filters

  1. Nov 20, 2015 #1
    Hi, I have read from previous topic regarding color of light vs wavelength. It is a bit confusing for on my self as I do not have any background on this. Hopefully someone could chime in and educate myself. Here it goes,

    it has been lingering in my head that the color of light emitted by a bulb (or any other source) corresponds to the wavelength. I am into corals and they need a specific light wavelength/ color (if I may say) which is around 430nm to 500nm to thrive base on my readings on coral propagation. Most light sources (fluorescent, LED) have purplish or bluish shade if we go for that range of wavelength. An example, actinitic light bulbs are on this color and fall within the wavelength range (430 to 485nm). Am I correct to say that my assumption or notion on color vs wavelength is correct?

    Another thing, I have read that using optical filters (glass or plastic sheets) could limit/filter the light on the discharge side. Say, I buy a PAR 38 LED bulb (daylight) then use an optical filter (plastic sheet or glass) to emit color or wavelength necessary for coral growth (which is stated above). Can I do this?

    I am trying to make my hobby more economical by enlightening myself (and others) using scientific facts. If the above is doable, this is great news.

    Please help.

  2. jcsd
  3. Nov 20, 2015 #2


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    This is a good concept for monochromatic light, it doesn't work if you have multiple wavelengths in the light. The color your eye and brain visualize then depends on details of the human eye and brain. Something the corals don't care about.
    The filter will remove some wavelength (range), it won't add light that was not present before. Check the emission spectrum of your available light sources to see if they have the right range in them.
  4. Nov 21, 2015 #3
    Hi mfb, thanks for your reply.

    For corals, different acropora species require different wavelength. This is being reflected on the coloration intensity that they show when subjected to correct light.

    The monochromatic type of light for corals are very costly, especially the led lights. This is the reason why I am trying to decipher the relationship of color vs wavelength and optical filters. If my guess is correct, it is cost effective and cost efficient to buy standard daylight bulbs paired with a highly efficient optical filter to deliver filtered light with specific wavelength range.

    With regards to optical filters: my bulb is rated as daylight and white in color. As per my readings, it would take a mixture of colors to create white. I only need the blue and indigo colors (430 to 486nm) which is present in white light. Correct to say that i could use optical filters to have light emission of this range for white light?

    i could not check the emission of light spectrum of commercially available, big box store type flourescent, cfl and led bulbs as they are not published and also not shown in the manufacturers website

    Sorry if i have confused you. I am just trying to educate myself.
    Thanks again for your help.
  5. Nov 21, 2015 #4


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    It is possible to get light that appears white without that wavelength range. Without the spectral data or details about the light production process you can't be sure.
    Blue LEDs shouldn't be that expensive. Their power consumption is significantly lower as well.

    I'm not sure if you need the filters at all: is additional light at different wavelengths harmful?
  6. Nov 21, 2015 #5
    Sir, thanks again for your reply.

    If I may explain, what I am trying to do is try to find out the el cheapo way of coral keeping. Lighting is one of the major expense of the hobby that has many myths.

    base on the experimentation done by one enthusiast, corals will thrive on the previously mentioned wavelength. Algae, on the other hand will grow on the yellow and red side of the color spectrum. And we dont want that.

    If I can use a regular cfl bulb and just add a filter to sustain coral growth, that would be nice. Then I can spread the word on it.
  7. Nov 22, 2015 #6


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    See some example spectra. There is probably some intensity in the right wavelength range.

    Okay, if algae grow using different wavelengths then filters sound useful.
  8. Nov 22, 2015 #7
    Thank you.
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