Developing Desire

 

We interviewed ETC software engineer Tim Robbins and hardware engineer David Cahalane about the development, science and art behind the new Desire™ line of fixtures – and how time at the gym is helping ETC make better LED luminaires.

Tim and Dave, there are powerful functional aspects of ETC’s Desire fixtures that take LED PARs to a different level. What were some of the challenges you worked on to make these better LED PARs?

Tim Robbins: One major requirement for our Desire products was color calibration. So two fixtures that receive the same HSI (hue, saturation, intensity) value, for instance, will match each other within a reasonable range of error.

Vendors ship LEDs to us sorted in batches, according to brightness range. The problem is that within the bins there can actually be quite a wide range of error in the color of the LEDs. So what we did is build a calibration instrument that records the wavelength data across the visible spectrum for each color of LED. Then it downloads that data to the fixture itself. So the fixture knows what it’s capable of and uses that data to figure out how to produce a particular color.

David Cahalane: Heat management has been another area of emphasis in the development of our fixtures, to work on the problem of ‘droop’ that all LEDs inherently have (the output of light is reduced as the temperature rises in the LED). So, we worked on solutions to regulate the fixture better thermally than other LED brands. 

First, we have a fixture completely naturally convection cooled. We spent a lot of time trying to make sure that we can get the most out of the unit under extreme operating conditions. We measure temperature at the different LED strings so we have real-time data on the thermals. 

We were also able to jump early on a new LED coming out. For the same current going into this improved LED, you use less power, which translates into less heat and gives us an immediate advantage, resulting in less droop.

Different LEDs are more and less susceptible to droop, right?

Cahalane: Right. For example, previous red LEDs had been notoriously bad. Your light could be cut in half over a period of time. The advantage of the new red and orange LEDs we’re using is what they call ‘low VF’ (low forward voltage), which translates into less power in the LED itself, less heat, less droop. One of the interesting things we found with some of our tests is that when we used some of these new reds with a fully hot fixture, we were getting more light out of the new reds than we were with a cold fixture of the old reds.

Robbins: We are also doing power regulation in the fixture to anticipate thermal droop. We don’t run the LEDs at their full power, and that allows us to increase power slightly as the fixture warms up. The idea is that the fixture will hold brightness and color as it heats up.

And holding color is definitely something a stage designer is concerned about. The Desire family includes a line of Studio fixtures, featuring the new white Rebel LEDs.

Cahalane: The Rebel ES is Luxeon’s energy-saving LED (“ES” for “energy-savings”). It’s a larger die physically, puts out more light for basically the same amount of power, and the thermal resistance is lower so that also helps with keeping the junction temperature lower and counters droop. 

So this Desire Studio LED fixture puts out more light than a lot of studio fixtures that are not using that particular Rebel LED.

Cahalane: Right. Same amount of power in, but you get more light output and less droop.

Cool. And you developed different operating settings for the fixtures. So when the fixture’s in Studio Setup, you have a different group of controls at the back and you’re able to set white points differently. How does that work?

Robbins: In a studio situation, the technician may not have a DMX console. At the fixture, the user can vary the intensity and the color temperature, and that will just follow Plancks Law (the Black Body Spectrum). Then we also give them the option to control the tint. It can either go more pink or more green.

Let’s talk about RDM in Desire. One of the goals of this fixture was to make it fully RDM compliant.

Robbins: When we started the project we wanted to just go with the basics – be able to discover the fixture and set the DMX address. Then as we were figuring it all out – what if someone wants to set this, what if someone wants to set that – we ended up going over the deep end a little [laughs] and  implementing everything on the back of the fixture, minus a few of the UI settings, that you can set and get from RDM. 

That’s a huge advantage because once the fixtures are hung all over these pipes in the theater, and then you decide “Oh, I want to turn Red Shift off because I don’t like the way it’s working…” 

Robbins: …you don’t have to get out ladder or anything. You can do it kind of remote control, just like channel surfing.

What are Desire’s Quick Setups?

Robbins: In case someone who didn’t know the fixture well felt overwhelmed by the options or they just didn’t need that many, we came up with some simplified settings. Basically, we created underlying modes for what someone using the fixture for ‘stage’ or ‘high-impact’ or ‘studio’ would want. 

So, if you select the Stage Setup, what happens ‘underneath the hood’?

Robbins: We gave you settings that make sense for theater lighting: ‘red shift on,’ ‘incandescent fade,’ that sort of thing. One of the coolest things about our Desire fixture is that we have recreated qualities that users like in their tungsten fixtures. So, when you dim down a tungsten-lamp fixture it shifts red (which is where we get “red shift” from), which is actually a flaw in the lamp source. So we’re almost replicating flaws in existing lighting, deliberately.

It’s like comfort food – nostalgia lighting. You like the way that light behaves. You’re used to it.

Robbins: In the Stage Setup, we’re also operating in a thermal-management setting where we’re holding color. A lighting designer sets a purple in the morning, the fixture runs all day. They want to come back in the afternoon, go back to that cue and have the fixture be the same color to their eye. This setting gives them what they expect.

Cahalane: In the Architecture Setup, we’re doing a different kind of thermal management. We’re actually doing what we call ‘power budgeting,’ which reduces the overall output of the light, but the tradeoff there is we believe we can run at more extreme conditions for longer periods of time without the fixture overheating. Imagine a fixture out in a theme park in the heat and humidity all day – especially a black fixture in the sun – it’s just a bad combination.

It’s like a black dog in the sun…

Cahalane: To simulate that extreme climate, we even put the fixture up on the roof of ETC’s building in the middle of August.

You guys put a lot of time and effort into these new Desire LED fixtures.

Robbins: You could say that [laughs]. One of my R&D coworkers, Troy Hatley, happens to go to the same gym I do, and we talked a lot there – running around and around the track – about how all this stuff could be done. So much so that we joked that ETC should probably reimburse us for our membership.