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Self preservation

Martin Professional’s Exterior 400 range uses colour calibration and thermal management to overcome some of the problems common to exterior LED luminaires. Ben Cronin takes a closer look

Exterior LED luminaires have come a long way in a very short space of time but, if you asked a lighting specifier to list his or her reservations about this type of product, there’s a decent chance that two questions would feature prominently in the response. The first line of interrogation would no doubt ask how the luminaire reacts to extremes of temperature; the second would probably question the colour consistency of the LEDs.

The Exterior 400 range from Martin Professional takes both of these concerns and tries to address them in a novel way. That the product recently won a product innovation award from US-based Architectural SSL magazine was at least partly due to what product manager Jonathan Meineke describes as its ‘dual innovations’. “The real story that overarches the whole range is heat management and colour calibration,” he says.

Heat of the moment

Like almost any LED product, the luminaire employs a heat sink to keep the LED array cool but where it differs is in how it responds to the extremes of temperature you might see in Africa or the Middle East. “There’s a heat sensor on the LED PCB that tells the driver in the control box if it’s getting too hot, so that it turns down the LEDs,” says Meineke. “It’s a very simple thing, but it’s not actually done by a lot of people.”

If this conjures up images of dimly-lit and ever-changing exterior schemes, Meineke is quick to add that the defense mechanism only activates in ‘extremely hot’ conditions, and even then, he thinks it is preferable to the alternatives. “In layman’s terms, I say the product goes to the maximum brightness that is acceptable for that ambient temperature, which in the vast majority means 100 per cent brightness,” he says. “But, if it gets incredibly hot, it dims down to protect itself. I think most designers would prefer a product that dims to, say, 90 per cent when it gets hot, as opposed to one that switches off completely, or one that keeps on running at full power and really degrades the LEDs.”

To explain at what point that dimming process might start, the product’s designer, Flemming Bjerre, suggests a junction temperature of 125°C would have a deleterious effect on the LED array. But the luminaire stops it from getting to that point. “We have an internal safety margin, but the product only dims so the temperature is constant,” says Bjerre. “Roughly speaking, it starts to dim when the ambient temperature hits 45 to 50°C and carries on dimming for temperatures beyond that. Theoretically, it could dim to 0°C, but most of us wouldn’t be around to see it if the ambient temperature reached the point where that was necessary.”

Life in colour

That deals with the thermal management of the product, but it is on the issue of colour consistency that Meineke really gets animated. “In my opinion, what we do with the colour calibration is the most interesting thing about the product,” he says.

Taking the RGBW unit as an example, he describes how each luminaire is tuned so that it will match exactly the colours of a corresponding fixture in the range, thus overcoming any binning issues with the LEDs in each luminaire. “At the factory, the fixtures are put into a machine which has a camera that tells each fixture how to adjust itself, so it gets the right mix of colour. Then that data is stored on the LED PCB so that each fixture knows its own set of co-ordinates. Each co-ordinate is going to be different for each fixture.

“If you look at the front of the fixtures you’ll see each one has a slightly different mix it has to do to get to the same colour point. By calibrating, you’re making sure each of the fixtures is putting out the exact same colour, so it doesn’t matter if, say, the red LEDs aren’t perfectly matched. That difference will be adjusted for by the greens, blues or whites.”

This approach even extends to a single-colour unit, the patent-pending, blue Exterior 430. “On the 430 unit, out of 56 LEDs, they’re all blue, except for four reds and four greens,” says Meineke. “That enables you to adjust the fixture to get the blue you want, but it also enables you to get the same colour out of the box. “In the majority of installations we find that designers want one colour. They’ll say: ‘I want blue, but I don’t want that blue’. Previously, the only way to solve that was by custom-making LEDs, which is very expensive. The other problem is the binning. If you had ten blue fixtures and you replaced one, there’s a very good chance you’d never be able to get those fixtures to match.”

Click here for a talk from Product Manager Jonathan Meneike

Inside Exterior 430

An interior look at the design of the Exterior 430

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