| Kevin Maxwell AKA TheMAXX wrote on Sat, 05 June 2010 19:46 |
From what I have seen of LED fixtures and I don’t know a lot about them so maybe someone will correct me. When looking into an LED fixture you don’t see the mixed color, you see the individual colors of the LEDs. You only see the mixed color on what the fixture is shinning on. So you don’t get that look of a gelled can from the audience perspective. And that is part of the lighting look.
I wish that the LED fixtures would look like a gelled light when looking into them. I think if they overcome that issue it would make them more usable. Someone on here had a workaround that involved a par LED with a deep enough fixture with a prismatic plastic piece on the front of it to diffuse the LEDs. I understand that it did absorb a bit of the light in the process.
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LEDs, unlike virtually all other light sources, emit relatively narrow-spectrum light (white LEDs get a broader spectrum by adding a phosphor). This allows for additive color mixing, instead of subtractive color mixing (color filters). For this additive mixing to occur within the fixture (and not in the space between the fixture and the object it is illuminating), either the output from all the LED channels needs to be mixed in some flavor of optical train, of the LEDs need to be packed close enough together so as to be perceived as a single source by the human eye. This last approach is a function of both the LED spacing and the viewing distance.
Mixing multiple color channels within an optical train isn't that difficult - it's done in 3-chip projectors all the time. The problem is that it's bulky, complex, and not horribly efficient. Very few fixtures are using this approach (I know of 2, both from the same manufacturer). Putting a diffuser some distance in front of the fixture is an example of this.
Getting the sources close together is the simpler approach, but it has its own collection of problems. First is that you need an LED package that has multiple color channels in the same package. Second, packing more LEDs (and thus more power) into a smaller area, the thermal management problem becomes more complex. Third, getting consistent color becomes more difficult because you can no longer bin each color individually - your package has multiple color channels, each with their own binning. So you've gone from x bins per LED to x^n bins, where n is the number of color channels. And then there's the sourcing issue. Not all LED vendors make multichannel packages, and those that do aren't putting their latest technology into those packages. The available multichannel packages are all a generation behind cutting edge (at least). Multicolor packages also have a larger emitting area, often with different optical centers for each color. This makes getting narrow beams difficult, if not impossible, at least if you don't want significant beam artifacts. The Elation fixtures listed are using a tri-LED, which puts 3 colors of LED in a single package, complete with all the associated drawbacks.
That said, colormixing within the fixture not only eliminates the "Lite Brite" look, but also helps to eliminate the multicolored shadows you get from LEDs that are spaced out. There are also advantages to spacing out the LEDs, instead of combining them all into a single source. Higher brightness, higher efficiency, and passive thermal management are all advantages of using multiple single-color LEDs.
As designers, though, we need to understand the different tools at our disposal, realize that each one has strengths and weaknesses, and choose the right one for the job at hand.
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