We've been trialling LED lights in our Southern Regional office and they've been working well with our Canon DSLR rig. We had a failure in one of our light banks and the replacement lamp was a subtly different colour to the other. We wondered - how can a light that's sold as daylight white (5600K) actually be different from batch to batch?
LED and fluorescent light is very different to incandescent light bulbs. In incandescent bulbs the piece that makes light produces light that is made up of all the colours in the spectrum. In contrast, in an LED or fluorescent light that piece that creates light produces light of a single wavelength - a bright blue. In order to make it look white, phosphors are added to change this colour to white.
Comparing Daylight and High CRI fluorescent lamps, daylight is comprised of an even spread of colours from Ultra violet through to Infra red. The colours close to the Ultra violet and Infra red aren't as defined in fluorescent light, and there is a "spike" in colour in the blue and green. Colours lack contrast when lit by fluorescent light compared to daylight making them slightly "flat" or dull.
The effect is even stronger when you look at the LED lights. The light still "looks white" to our eyes, but to a camera device it really only sees a strong light blue and a yellow, with a small amount of greens and reds.
Manufacturers use a method of sorting whereby LEDs are categorised by lumen, colour temperature and voltage - and this small amount of tolerance makes a real difference. Enough to make one light bank not look like another light bank. This is why, if one of your LED light banks fail, you'll need to replace both of the banks.
For more in-depth explanation of LED vs Fluorescent lighting, download our PDF.