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post #6 of (permalink) Old 07-05-2012, 06:40 AM Thread Starter
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Emitter Layout

6. Emitter Layout

How far apart should I space them?

This will depend on several things: What emitters are you using? What current are they running at? What height are they from the substrate? What are the dimensions of your tank? What PAR are you trying to achieve? What optics are you using? Fortunately, Hoppy has done the work for us with his Excel Calculator.
What pattern works best?
Pattern isn’t as important as spacing - unless you are blending different colors. Whatever pattern you use, even spacing of emitters will provide the most even coverage. To avoid cool/hot spots, make sure the emitters are evenly spaced in all directions. Consistent patterns with blended colors will limit bizarre shadow patterns and disco effects.
How do I get the best shimmer effect?
Fewer emitters = stronger shimmer, but watch out for spotlighting!
What is spotlighting?
Spotlighting occurs when there are not enough LEDs to fully saturate an area with even coverage of light. This results in areas of intense light surrounded by areas of less intense light creating bright spots. If this in itself doesn’t bother you, know that is will likely lead to plants “leaning” toward the more intense light cones, and possibly insupportable PAR in the dim areas. While completely eliminating spotlighting by cramming a fixture with emitters is possible, it is quite a bit more expensive than simply calculating the minimum necessary for even coverage for your particular tank, and spacing the emitters appropriately.
Remember to think 3-dimensionally!

The beam spread of an emitter crates a cone of light that is narrower at the top than it is at the bottom. Your plants fill the full 3-dimensions of your tank, so you may not be spotlighting the bottom, but the top could have dark and bright spots, leading to plants leaning near the surface of your tank. Work for close to even coverage from the substrate all the way to the surface! Here is a great example diagram testing several layouts for coverage that provides a great 3-D picture of what the light cones look like.
What is the disco effect?
Reefers talk about the “disco” effect. This happens when you use multiple colors that are spaced too far apart, or spaced unevenly or in different quantities.

LED’s are different from fluorescent lamps. Fluorescents produce a diffused, largely even spread of light in every direction from a relatively large surface area. LED’s are what is referred to as “point source emitters” meaning that the light is produced by a very small surface area. This creates a crisper, more focused light that renders very sharp shadows and a cone-shaped area of highly focused, intense light.

If you have a red light and a green light striking an object from different angles, the area lit by both lights will appear “white”, and the shaded areas will appear in bolder colors. Adding a red light to the green side and a green light to the red side will help, but the positional difference will still result in “disco” colors in the shaded areas. The more colors you use, the more colors you will see in the shadows. Cree has produced a "3-up" star that is supposed to limit the impact of this effect by placing 3 emitters in popular color combinations on the same star.

Here is a picture that demonstrates an example of what disco looks like:

Photo from:

Last edited by theblondskeleton; 07-20-2012 at 08:59 PM. Reason: fixed link
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