Understanding RGB LED . Mythbusting

Discussion in 'Lighting' started by Jamie@Vertex, 30 Oct 2011.

  1. Jamie@Vertex


    Posts: 189
    6 Aug 2011
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    With all the hype going on with RGB (red, green, blue) LED combinations, I wanted to take a moment and explain some of the mythology associated with this approach. I know we are all fascinated by a potential magic bullit.

    First, we need to understand what light is and what light LEDs produce. Most of us know that visible light is but a splinter of the electromagnetic spectrum, which includes wavelengths such as infra red (heat) to gamma radiation (destroys living tissues). LEDs are a technology that can produce very specific radiation wavelengths. We are familiar with the current favourites such as Royal Blue (450nm), Blue (470nm) and Cool White (a phosphor LED with a mixed spectrum peaking elatively low in the yellow-green and high in the royal blue). These are all within the photosynthetic spectrum, often called PAR (photosynthetic active radiation). This is essentially visible light. Depending on the organism, various parts of this spectrum are utilized for their photosynthesis. This is an evolutionary adaptation which allow the organism to thrive in its given environments. Needless to say, the actual parts of the PAR spectrum utilized can vary greatly. Land plants utilize most of the red to far red spectrum, as well as the blue to UV spectrum. Sea plants, such as zooxanthellate alga, use mainly the blue spectrum, as this is most abundant in shallow seas. The red is simply filtered out in the first few meters of water and thus not available for photosynthesis.

    Now, this demarcates the area of useful radiations for any given environment, which we often refer to as PUR (photosynthetic utilized radiation). For our marine aquariums, this embraces the spectrum from about 530nm down to 380nm, of which most of the PUR is between 400nm-500nm with strong peaks at about 410nm and 450nm, give or take a little. This makes radiations outside of this spectrum less interesting for our corals and most other creatures found on the average reef, which is typically 10m deep or more (the exception being tidal reef tops, of course).

    Now, with this base information in mind, let us look at RGB lighting. We can simply say we have radiations at 470nm (blue), 530nm (green) and 630nm (red) from the get go. Of these, the blue is the most usefull for corals, although it peaks a bit high. Many animals do use this spectrum and it does enhance many fluorescent pigments. A definite win for the aquarium. The green radiation comes on the border of usefull radiation. For photosynthesis, it is largely useless, but for the production of certain pigments or at least their fluorescence, it is usefull. On the other side of the coin, it starts the range of cynanobacteria PUR, which then runs up into the yellow. It is a radiation to enjoy in smaller amounts and with some caveats. Now, the red, at 630nm, is at the start of the classic land PUR for very shallow water life forms. It will encourage certain alga, but, interestingly enough, will actually restrict the populations of zooxanthellae in a coral! (this may be guild related). An interesting quality. In very large amounts, it could potnetially damage or even kill a coral via bleaching, while in controlled amounts will aid in modeling the colour of corals via this zooxanthellae restriction. It is an area that needs to be better researched.

    OK, this alls sounds fascinating, but what about all the cool colour blends one can create with an RGB set-up? Yes, with these colours one can visually mix any given colour (within reason, as colour is a bit more complex) for their aquarium. Our eyes will be quite happy with the results. However, to attain the humanly aesthetic results, we are tricking ourselves into believeing that our corals are getting what we see. Let me explain.

    Our eyes will mix received radiation and create colours that are radiation-wise not there. For a simple example, a combination of red and blue light will appear violet to our eyes. This is not violet radiation! If we analyze the spectrum, we will find that it is still a combination of 450nm and 630nm, not a true violet at 420nm! The same is true for any visual colour effect mixed via this method. It is the same thing we see in printed materia, where we are using cyan, yellow and magenta with black to create the entire rainbow. Our eyes are tricking us into see what we have lead them to see. Actually, a very cool thing, as, without this, colour printing would be close to impossible. Many will remember from school tha the cones in our eyes detect specific groups of radiation with preference, creating wehat we call trichomatic vision. The cone receptors of our retina interpret blue-violet, green and yellow-orange (red) wavelengths into the complete rainbow or possible colours. Of course, our corals do not see the world through our eyes and, with a RGB spectrum are missing much of the vital radiation they need to fill their PUR spectrum. The bottom line is: if the radiations are not produced by the light source, it is simply not there! Regarless of what our eyes are trying to relate to us.

    This is not to say that RGB is a bad thing, simply that one must understand what one actually has. As a supplement to a good PUR spectrum, it does allow the aquarist more scope in mixing the aesthetic. It does not substitute for missing parts of the electromagnetic spectrum.

    If you have questions, do ask. Many of the obvious questions can be better answered with a Google search, where you will find in-depth discussions of human vision and the visible spectrum, as well as PUR and PAR.
    Last edited: 30 Oct 2011
    dallasg likes this.
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  3. Yuri


    Posts: 1,999
    9 Jul 2008
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  4. Dirkie


    Posts: 171
    20 Mar 2013
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  5. stevenfryman


    Posts: 1
    25 Jun 2013
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    Which light strips?

    I need help designing a main lighting for my 120 gal freshwater aquarium
    It's about 20" deep and is heavy planted.. I want strong plant growth, I would like to use light strips! Thanks for any help.
  6. Snoek


    Posts: 926
    12 May 2013
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