NAB 2013: Properly Engineered LED's

Posted by Phil Rhodes
Apr 09 2013 05:17 PM

I've spent a while today walking around all of the places hawking LED lights - which is a lot of places - challenging each of them to explain why their particular LED lighting devices produce acceptable colour rendering for film and TV work, given that we now know the traditional CRI assessment does not adequately characterise discontinuous-spectrum sources in that regard.

Most places responded with phrases along the lines of "It's got high CRI, stop asking awkward questions. The one single outfit that didn't was the company BBS Lighting, who make the Area 48 light. Four of them look like this:

Since the scale isn't necessarily Each subunit is about a foot on the long side. The diffuser is actually a phosphorized panel that's removable. Taken off, you can see the blue LED emitter elements which drive the phosphor:

They're so intense, there's a safety interlock to prevent you burning a regular pattern of little holes in your retina when the phosphor panel is removed.

This is good, because you can remove the phosphor panel and replace it with one which produces a different colour temperature, or even, soon, coloured light for effects or illuminating chromakey screens. This approach also gives the company a lot more granular control over how the things behave, since it can specify any phosphor for the panel and develop those phosphors independently of the LED driver technology. Most approaches rely on an LED driver that's a solid block of plastic with the phosphor and diode junction sealed inside, which is much less flexible. The company also makes all the right noises about thermal management (and remember the phosphor isn't attached to the heat-generating LED in any case), including making it clear that you can leave them on for hours in an un-air-conditioned barn in Death Valley in August and they won't get dimmer as the thermal management circuitry kicks in.

Now, this isn't the first time this has been shown (they were at BVE in London a few weeks ago), but it is the first time I've ever had anyone correctly refer to the much more recent Television Lighting Consistency Index (read about it in this EBU article). While this is really designed quite specifically to evaluate lighting for television, TLCI certainly a much more comprehensive analysis than CRI and any light which scores high for TLCI is much more likely to be suitable for critical work.

So, full marks to BBS Lighting!

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