Thursday, October 6, 2011

The Academy on LED Lighting Technology

BETWEEN 2% AND 10% of a motion picture's budget is for lighting, and if we consider that much of that cost is for electricity and for the purchase of low-life expectancy lamps, then new technologies look quite promising. Solid state light emitting diode (LED) lamps produce great amounts of light at low power consumption, they don't generate much heat, they have a long life, they are lightweight, and they are tough, making them unbreakable and safe to work around. The new solid state lighting has many benefits, and the United States government is heavily encouraging its use.

The Academy of Motion Picture Arts and Sciences is studying the new LED lamps for suitability in motion pictures. Their preliminary research can be found at the Solid State Lighting Project page.

The results are not good. LED lamps do not present colors very well to the camera.

Generally speaking, according the presentation linked above, LED lighting is currently a poor choice for getting good color, most particularly for getting good skin tones, which are particularly harmed. The example tests show skin looking more green and sickly instead of having a healthy ruddy glow. The tests show also that makeup looks inconsistent under LED lighting, and does not blend as well with bare skin. Tans, light browns, and reds tend to be harmed significantly, while some blues are enhanced. Colors in general appear to be less differentiated under LED lighting, and complex fabrics tend to 'flatten' and have less pronounced shading and texture. The use of these lights could impose greater costs, requiring color checks before filming.

Tungsten lamps and daylight produce a flat, uniform spectrum, and so are perfect at rendering colors accurately. Film stock and digital sensors render the colors from this kind of lighting very well.

In the Academy's opinion, the discontinuous spectra produced by LED lighting is problematic. The terms 'color temperature' and 'color rendering index' are not particularly useful when discussing LEDs, because of their discontinuous color quality. A solution, they think, may not be in improving the LED lamps themselves, but rather in developing custom film stock and digital sensors that better match the LED spectra. They also think that custom discontinuous filters could be used, but this will remove much of the electrical efficiency of the lamps, making their use largely moot. These fixes are not likely to help photographers who are much less in control of their lighting, and who need more general-purpose equipment — an LED optimized sensor would do a rather poor job under daylight.

Visually, the various light sources look the same to the human eye: but the camera does not perceive light the same way and colors are rather unpredictable. I ought to note that much research is currently being done to make a visually balanced LED spectrum, but this by no means is expected to work well with photography. Every model of sensor will have a different response to the LED lighting, making color matching more difficult.

The Academy thinks that LED lighting products are being rushed to market without taking into concern the needs of quality color reproduction. They also see the need to have quality third-party evaluation of the products emphasizing cinematography.

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