Viewing LEDs in A Different Light

It was impossible to imagine that these dim, monochromatic, red indicators could ever become a useful source for illumination.
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Despite my (well-deserved) reputation for being a tech-head who always wants to try out the latest technologies and ideas, I remain very conservative with the light sources I choose for creating pictures. When it comes to making images of familiar things like peoples' faces and clients' products, I am ever-so-slightly obsessive about color accuracy.

While I'm well aware that our beloved viewers have the power to completely nullify our efforts at color accuracy with the press of a key on their remote control, I nevertheless hold firmly to the ideal of supplying them with better quality images than they rightfully deserve. One consequence of this conservatism is that I have regularly been among the last to move to new generations of light sources for portraiture and product lighting.

As an enthusiast who has been playing with electronics since the age of eight, I was fascinated by the idea of LEDs, and used them as indicators on my projects as soon as I could afford to buy a few from the electronics parts store. It was impossible to imagine that these dim, monochromatic, red indicators, which were so easy to burn out when prototyping, could ever become a useful source for illumination. And for a very long time they weren't.

THE EFFICIENT LED

The LED's main strength—its high efficiency at just one wavelength—is also its major downfall for general lighting applications.

The familiar traditional light sources such as the sun, oil lanterns, fires, candles and even filament electric lamps, all produce light by heating something up until it glows (incandescence).

The heating process produces a very broad mix of light wavelengths, which we identify as "white" light. Unfortunately almost all of the light produced in this way is in the invisible infrared band, which doesn't help our eyes to see or our cameras to shoot naturalistic pictures. Incandescent sources have a deservedly bad reputation for energy efficiency.

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The Litepanel Micro in use on a Panasonic camera The light-emitting diode chip, on the other hand, uses a much more refined physical process to produce just one wavelength of light, much more efficiently than simple heating. The output wavelength depends on the mix of semiconductor materials that the diode chip is built from. As longer wavelengths such as infrared and red light are the easiest to cajole out of semiconductor chips, LEDs of these wavelengths were the first available. We continue to use high-efficiency infrared LEDs in the vast legions of remote control units that burrow into the crevices in our furniture.

Further developments in LED semiconductor materials eventually led to the production of shorter wavelengths and hence to yellow, green, cyan, blue, mauve and eventually even ultraviolet LED chips.

It became possible to cluster a selection of LEDs together to produce a mix of wavelengths that roughly approximate the white light from incandescent light sources. These clusters are what we see used in LED display screens and in the variable color LED effects lighting that appears everywhere in contemporary television production, from talent search and game shows to news sets.

While producing white light for general purpose illumination is clearly possible with clusters of LEDs, it is neither a particularly cheap nor particularly energy-efficient approach.

The overwhelming majority of today's white LED light sources are based around a single blue-emitting chip embedded in a fluorescent phosphor material that glows yellow when illuminated by blue light. The resulting (blue + yellow) light from the LED appears to be a cool white, and everybody applauds the application of this new technology to the current problem of energy efficiency.

THE PROBLEM IS...

Today's LEDs may be thousands of times brighter than their forbears, but they still need a protected and nurturing environment to thrive, and are usually being driven so hard that they require complex heat management strategies to avoid self-immolation.

The really big problem with the modern white LED, however, is that the output spectrum often has a noticeable magenta cast and is more than a little lacking in the red area of the spectrum, the very area that is so important when lighting skin tones.

Given my trepidation at using LEDs for production lighting, it was very interesting for me to receive a Litepanels Micro softlight to evaluate. Part of a well-designed system of light sources, mounting accessories, battery packs, power supplies and filter frames, the three-watt Micro is very cute, but just doesn't pack enough punch for the work I was doing at the time, so I passed it on to Pete, a news cameraman friend, for a workout.

Since the Micro runs for over an hour on just four standard alkaline AA cells, he used it as a soft fill for close-ups when he was in a hurry and didn't have time to set up a utility-powered light source.

The Litepanel really came into its own when Pete was sent on assignment to cover the inaugural flight of a new air route to the Antarctic, but given an absolutely miniscule weight allowance for his camera gear. The only lighting equipment he took with him was the little LED Litepanel and a box of AA ProCells.

Judicious selection of camera positions and the battery-powered LED softlight to fill the holes enabled him to get the quality of results that he had hoped for, despite the serious baggage restrictions. After the Antarctic trip the Litepanel came out more often and was passed around between news crews who were shooting in unusual locations.

The news cameramen were impressed with the concept of the Litepanel softlight, even though the Micro was sometimes struggling to produce enough light to do the job. Its built-in dimmer rarely ran at anything less than 100 percent.

As a result, they pushed station management to purchase the Micro's larger (8.5 watt) sibling: the MiniPlus. The news crews now have a single-head kit and a dual-unit kit of MiniPlus units, complete with lithium ion battery packs, chargers, filter and diffuser kits, and a range of mounting brackets and other grip gear. I recently had an opportunity to use the MiniPlus heads on a shoot that was part of a lighting course for would-be cinematographers and was impressed with their output considering their size, weight and portability. The Litepanels were also borrowed from the news department for a night shoot for a small drama production. They acquitted themselves very well, especially when mounted on microphone fish poles and surreptitiously slipped into the setup as the Steadicam tracked in from an ultra-wide shot to a medium close-up.

Everything I've learned about the Lightpanels is very positive, with the sole exception of their color rendering. When used in the field for capturing news footage on the run, a highly efficient, lightweight softlight is a bountiful blessing. Getting an image at all is a major achievement in some news situations, so if the skin tones have a magenta cast in places, while not exactly ideal, it's still acceptable. After all, the dichroic daylight correction for the Quartzcolor Redheads was always noticeably magenta, and they saw action around the world for decades before the advent of portable metal halide fixtures.

When used in conjunction with other nominal "daylight" color temperature sources, the news cameramen have found that a 50-percent covering of half-density plusgreen fluorescent correction gel (Cinegel 3315/Lee 245) takes care of the magenta cast. However, I would want to do some more controlled camera tests before mixing these LED sources with HMI, daylight or tungsten on something as critical as a studio talking head or a client's iconic can of rich, red tomato soup.

Andy Ciddor has been involved in lighting for more than three decades as a practitioner, teacher and writer. You can reach him via e-mail c/o TV Technology.