LEDs: Much more than meets the eyes

LED lighting technology is being deployed at pace in broadcast studios, and increasingly for feature film with the promise of significantly reduced running costs, yet the marriage of LEDs with digital cameras can produce alarmingly different qualities in color reproduction.

In an illuminating explanation of the color science behind traditional and new lighting technologies at the Technology Summit on Cinema, Ryan Fletcher, LED Product Manager at ARRI, drew attention to the disparities in color rendition that different LED light sources output.

“With digital imaging and LEDs there is much more than meets the eyes,” Fletcher said. “If we can’t trust a meter or our eyes – how we do know how to light talent with white LEDs?”

Fletcher explained that a white LED has not in fact been invented. Instead, white LEDs can be made by combining RGB LEDs or by placing a phosphor filter over a blue LED.

“This is important because LEDs make white with a discontinuous source,” he said. “When that is combined with a discontinuous method of capture - which is inherent in the sensor technology of all digital cameras - then we are faced with some scary consequences of bad color reproduction.”

A series of tests comparing subjects shot with tungsten with different LED sources illustrated this. Each of the white LED sources produced subtly different color reproductions – some as good as tungsten, others significantly worse.

“A white LED light will look white to the human eye and the measurement tools which we have been using for years will tell us that is white, yet when we examine the light’s spectral distribution [with a spectrometer) the color rendition can look startlingly different,” he said.

“The upside is that you can get very good lighting with LED but it requires more investment in time and in tools to test, you get great efficiency and a key advantage is the ability to tune the color by using different LEDs.”

Plus, he said, LED technology continues to improve. “In ten years we won’t be talking about LED and color – but it is a topic that we need to address today.

Tungsten technology is essentially unchanged in 100 years and it remains the most popular lighting source and the main reference light. But 95% of the electrical energy is converted into heat. 

“One of the pushes is financial,” said Fletcher. “When you install a studio with tungsten you generate a lot of power, a lot of heat and a lot of air con. If you go LED you get rid of power and reduce the AC by a factor of 4 – and your talent stays cool. The advantages in terms of ROI are quick to realize – we just need to be aware of what we are dealing with.”