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LED Beam Blending
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<blockquote data-quote="Rob Timmerman" data-source="post: 15396" data-attributes="member: 172"><p>Re: LED Beam Blending</p><p></p><p>Since you are looking for a relatively wide beam when using these fixtures on the upstage truss, you may have some luck putting the diffusion (or other beam spreader, such as a prismatic lens sheet) beyond the mixing distance of the fixture, so that mixed colors hit it.</p><p></p><p></p><p></p><p>Some background, shamelessly copied from a previous post of mine on another forum:</p><p></p><p></p><p></p><p>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.</p><p></p><p></p><p></p><p>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.</p><p></p><p></p><p></p><p>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 [Elation OPTI TRI 30] listed are using a tri-LED, which puts 3 colors of LED in a single package, complete with all the associated drawbacks.</p><p></p><p></p><p></p><p>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.</p><p></p><p></p><p></p><p>The information I have on the Elation fixture comes directly from Elation's datasheet <a href="http://www.elationlighting.com/pdffiles/opti-tri30-cutsheet.pdf" target="_blank">http://www.elationlighting.com/pdffiles/opti-tri30-cutsheet.pdf</a></p><p></p><p></p><p></p><p>There are some photos on page 2 of that datasheet that show the front of the fixture when it is mixing between 2 colors. Of interest is the photo where the fixture is producing magenta, and you can clearly see that the red and blue beams don't overlap perfectly. This issue is an artifact of the narrow optics and the fact that a tri-LED has a different optical center for each color. [LED optics are typically imaging optics]</p><p></p><p></p><p></p><p>''Binning'' is a way of quantifying the inherent variation between LEDs as they come off of a production line. Every manufacturer does things a bit differently, but a google search for ''LED binning'' turns up some useful info</p><p></p><p></p><p></p><p></p><p></p><p>And in the interests of full disclosure, I work for Philips Color Kinetics, a manufacturer of LED lighting fixtures.</p></blockquote><p></p>
[QUOTE="Rob Timmerman, post: 15396, member: 172"] Re: LED Beam Blending Since you are looking for a relatively wide beam when using these fixtures on the upstage truss, you may have some luck putting the diffusion (or other beam spreader, such as a prismatic lens sheet) beyond the mixing distance of the fixture, so that mixed colors hit it. Some background, shamelessly copied from a previous post of mine on another forum: 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 [Elation OPTI TRI 30] 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. The information I have on the Elation fixture comes directly from Elation's datasheet [url="http://www.elationlighting.com/pdffiles/opti-tri30-cutsheet.pdf"]http://www.elationlighting.com/pdffiles/opti-tri30-cutsheet.pdf[/url] There are some photos on page 2 of that datasheet that show the front of the fixture when it is mixing between 2 colors. Of interest is the photo where the fixture is producing magenta, and you can clearly see that the red and blue beams don't overlap perfectly. This issue is an artifact of the narrow optics and the fact that a tri-LED has a different optical center for each color. [LED optics are typically imaging optics] ''Binning'' is a way of quantifying the inherent variation between LEDs as they come off of a production line. Every manufacturer does things a bit differently, but a google search for ''LED binning'' turns up some useful info And in the interests of full disclosure, I work for Philips Color Kinetics, a manufacturer of LED lighting fixtures. [/QUOTE]
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