Taming LED’s Color Issues

Vendors look beyond CRI for more accurate rendering.
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SEATTLE—When LED lighting fixtures exploded on the cine, video and television scene, one of the first things that early adopters discovered was that all LED lights weren’t created equal, especially in the area of color rendering.

Complicating the problem was that you couldn’t measure color rendering by eyeballing it.

“When you look at visible light, it has all the colors of the rainbow, all the way from infrared to ultraviolet,” said Jose Maria Noriega C.A.S., president of professional lighting provider Fluo-Tec. “Of course the eye will try to compensate for color aberrations.”

A film or digital camera is nowhere nearly that forgiving when displayed on a high quality, well calibrated monitor. “The best lighting equipment will provide colors as accurately as the eye sees it,” Noriega said.

WHAT YOU SEE IS WHAT YOU GET

The Color Rendering Index (CRI) rode to an early rescue by measuring a light fixture’s rendering of eight colors. The CRI results measurement ranged from zero to 100%, 100 being a perfect score.

The original Color Rendering Index (CRI) samples included no saturated colors.

The original Color Rendering Index (CRI) samples included no saturated colors.

“The problem with that is those eight colors are all light pastel shades,” said Pete Challenger, who manages U.S. business development for Italian-based lighting vendor Lupo. “So you can have a light that’s rated 98 CRI that makes people look like corpses.”

More sophisticated color measuring systems have been developed. One is an expanded CRI that includes 15 colors, including saturated colors. The Television Lighting Consistency Index (TLCI) uses a software program to calculate a score. And a Spectral Similarity Index (SSI) system is being developed by the Academy of Motion Picture Arts and Sciences.

Seven additional samples to the Color Rendering Index (CRI) added saturated colors.

Seven additional samples to the Color Rendering Index (CRI) added saturated colors.

But Challenger is feeling pushback from customers. “[They’re] coming around to what we’ve been preaching for years: the only real way you can assess a light is to point the camera at the kinds of thing you point cameras at, lit by that light, and see what it looks like on that camera.”

Al DeMayo, co-founder and CEO of Litegear, pointed out that as professional lighting people learn more about color science, “they’re starting to ask for things that not only help them do their jobs easier, but also make them better at their own job.

“In the past, with incandescent fixtures, you had tungsten-balanced film and that’s a perfect white balance,” DeMayo added. “But today, with digital cameras and programmable LED fixtures, that white balance is a moving target.”

He noted that one anomaly in bicolor lighting fixtures is that while their color rendering might be near perfect at the daylight and tungsten white light extremes, “it’s a little magenta in the middle.” To counter that, Litegear and others have added saturated red, green, blue and sometimes other LEDs to balance out a magenta or green shift.

MACHINE LEARNING

BB&S Lighting’s founder and owner/co-founder Peter Plesner noted that color shifting is even more complicated when a bi-color LED lighting fixture is dimmed while the color temperature is in the middle of its color temperature range.

Litegear recently introduced its S2 LiteMat, which it says is nearly 40% brighter than the original LiteMat, has better color quality and a widely extended Kelvin range all without an increase in power draw. In addition, overall CRI increased to 95+ with a matching TLCI of more than 95 as well.

Litegear recently introduced its S2 LiteMat, which it says is nearly 40% brighter than the original LiteMat, has better color quality and a widely extended Kelvin range all without an increase in power draw. In addition, overall CRI increased to 95+ with a matching TLCI of more than 95 as well.

“We have a lot of algorithms we’ve developed to correct that. It’s been kind of like machine learning,” he said. “This technology is something we’ll be using in all of our color lighting products in the future.”

All customers are concerned about color accuracy, according to Byron Brown, product manager for Litepanels.

“But depending on the customer, they’re going about it in several different ways,” he said. “Those at the less sophisticated end of the spectrum, are looking at indicators like CRI. Or maybe some of them have progressed into a TLCI kind of measure, and as long as your number is high, then they’re OK.”

Many of Litepanels high-end customers start there, but then they do their own measurements, Brown added. “And these are either with a meter, or in many cases they’re actually measuring with a camera,” he said.

Brown said that where his company used to have to do a lot of custom work on LEDs, now many LED makers have adopted those kinds of technologies as a matter of doing business.

Kino-Flo has developed its newest firmware to allow “all of our soft lights to match the color spectrum on the cameras being used in the studio,” said Scott Stueckle, sales and public relations manager. The company has done a series of tests in studios where the use Kino-Flo’s lookup tables (LUTS) to match to the camera’s spectral curve.

“If you wanted to take a Kino Flo fixture and match it to some kind of a light source in a shopping mall or something like that that’s a little different, you can do that. You can take a meter reading and get the XY coordinates, and match our light to that ambient light.”

MISSION-CRITICAL

Color accuracy in terms of white light is absolutely mission critical, according to Rich Pierceall, CEO of Cineo.

“One of the things that digital lighting provides for us is the ability to customize the spectrum,” he said.

Pierceall pointed out the look the production crew is after may not be a numerical color temperature match. “What we have focused more on is the red end of the spectrum, primarily because people are red, and we want to make sure that when a camera captures an individual, that person looks healthy,” he said. “That generally means giving them a heavier representation in the deep reds.”

Last month Cineo was acquired by NBCUniversal. The Cineo brand, its products and staff all remain intact, according to a company spokesperson.

UNIT-TO-UNIT CONSISTENCY

All of ARRI’s color science is based off of calibration, according to Mike Wagner, senior product manager for the company.

“Every single fixture that leaves our factory, is calibrated,” Wagner said. “That process allows us to identify the exact wavelengths and LEDs and everything within that particular fixture. We can store that information on the fixture.

“Then we’re doing our color science math on that fixture with that information, and that allows us to get very, very accurate results,” Wagner added. “So we’re now using a kind of lookup table, we’re using the data from the LEDs within that fixture, and that gives us really high grade unit to unit consistency. That also allows us to hit very accurate color points because we know what the LEDs are doing and how to control them. That’s really the key to what we’re doing.”

Though none of the lighting fixture manufacturers make their own LEDs, “it really starts at the chip level” when it comes to color rendering, said Craig Asato, product manager at Zylight. Lighting makers “will pay a little more for tighter binning on the production lots. Chip manufacturers have different binning levels,” and for the best color rendering you want the best of the best LEDs.

Tighter binning “means we’ll pay the cost goes up, because the yield from the chip manufacturer’s standpoint goes down,” Asato added.

In the future, look for even better ways of evaluating the color rendering in LED fixtures.