Colour mixing great by Phil Rhodes – ProVideo Coalition – ProVideo Coalition
Exactly how we get here is not as important as where we’re getting to.
Recently, the world has become very excited about the technologies underlying colour mixing LED lights. Here’s why we shouldn’t.
It’s been a while since LED lights have generally been able to do what they’re intended to do, and do it pretty well. Even the quest for higher power is starting to encounter the reality that the bigger they get, the smaller the market is, particularly once power levels exceed the capacity of the 15-amp NEMA connectors common in American domesticity. Other problems are simply hard to solve: finding two lights both described as “daylight” from different manufacturers which actually, visually match is still more difficult than we’d all like it to be.
The sunlit uplands are perhaps not quite as evenly sunlit as they should be, even if modern full colour mixing lights can solve the problem given a bit of tweaking. Overall, though, after a decade of madcap innovation, things are perhaps calming down a little.
“How I love my coat of many colours”
How colour mixing mixes colours
Consider the tendency for everyone to become concerned about the technology underlying colour mixing lights. No longer is it enough for lights to change colour; the manner in which they do so is now a point of contention. Lights based on red, green, blue and (one or two shades of) white LEDs now compete directly against those with red, green and blue plus amber, cyan, lime, and other things.
The problem is, that’s still too simple a way to describe the technology. Even if we have two lights using similar emitter configurations, there’s at least two major ways to create red, green and blue light with LEDs. Direct-emission types use different materials in the structure of the LED emitter itself to change colour; phosphor-converted types use a blue or violet emitter to excite a phosphor that emits light that isn’t blue or violet.
The advantage is a less saturated colour; a less spiky spectrum. The disadvantage is that phosphor conversion is an inefficient process, particularly in the red, which is why colour mixing lights using phosphor-converted red often have a large preponderance of red emitters. The choice is to trade off some efficiency for the broader, potentially kindlier spectrum of phosphor conversion, or to trade off some colour quality for output and efficiency. Welcome to the engineering compromise, and that’s just one specimen of the many engineering compromises involved in LED lights.
Whether or not a light is using PC emitters makes possibly at least as large a difference to its output and colour quality as the emitter configuration. For a start, there aren’t really PC green LEDs which are realistically available to people designing lights – well, there are, but the closest option is what’s usually called lime in the RGBACL combination. It’s a fairly unsaturated mint, and while lights have been made using that as the only green, the result has good colour quality in whites but can’t produce a deep emerald. Phosphor red is inefficient, and still less saturated than direct red, although to a great extent the broader spectrum is the point of phosphor conversion.
But do you want a nice powerful Star Trek alert red, or subtle tints of pink?
LED video walls suffer many of the same …….