New Lighting Buzzwords
Recently I wrote a post “In the Studio with LED Lighting.” Since then I attended the WPPI trade show that brought me in contact with lots of new lighting systems and I wanted to update and expand that post, which is what I am doing today…
Working with LED lighting systems brings you face-to-face with terms like lux, lumens and foot-candles but don’t freak out, there was a time when megapixels were alien too. A lumen aka luminous flux is a small unit and equivalent of 1.46 mW of radiant electromagnetic power at a frequency of 540 THz. Lux is a unit of illumination equal to one lumen per square meter or the equivalent of 0.0929 foot-candles. Sekonic’s chart compares Exposure Value to foot-candles and lux. Charts, like Jim Beecher’s, convert EV numbers into shutter speed and lens apertures if only on an order of magnitude basis, such as when you discovered that the Nikon D800 had 36.3 megapixels, you knew “that’s a lot of megapixels.”
Some WPPI presenters were talking about “this new thing called CRI” but the Color Rendering Index standard was introduced in 1948. CRI has a scale from zero and 100 that measures a light source’s ability to accurately reproduce color. A CRI number is determined by comparing the color rendering of a test source to that of a perfect source and uses a standard formula averaged over the number of samples to get the final rating. At 80 a light reproduces 80% of the visible color spectrum while a CRI of 100 accurately reproduces the colors found on a sunny day at noon.
For photographers serious about their craft, it’s not just the way that light from LED sources are measured it’s also the quality of that light that’s important. Not all LEDs are created equal and based on my experience testing several different systems there doesn’t seem to be a direct correlation between price and quality. Although some cheap LED lights reflect their price point others are surprisingly good, just as some expensive LEDs systems are not that great producing a spectrum with missing color and spikes in others. Your eyes automatically adjust for any missing color bands or spikes but your camera cannot do this and any difference results in more time spent in the digital darkroom trying to get the color right. To give me a handle on this aspect of LED lighting for future lighting system reviews I obtained a small Diffraction Grating Spectroscope at WPPI that will let me visually inspect a light source’s spectrum and actually see peaks and missing color bands.