How good is your light?

The human eye and the camera sensor do similar things. But they are not the same and sometimes that matters.

Our ability to interpret images and compensate for visual defects helps us get through daily life, but this can make us poor judges of artificial lighting. As a result, most of us can’t tell a cheap LED bulb apart from a premium model, a professional fluorescent from a cinema tube.

 

The digital image captured by a camera sensor is, however, quick to show up green hues or poor skin tones. When clips are graded in post, these errors become real problems, with the editor or colourist unable to correct for poor lighting. Gaps in the light spectrum create an image that can look well exposed but may be impossible to match with other pictures.

Officially Speaking

Help is at hand from the EBU and its TLCI scores which accurately and scientifically test the output of LED lights. The often quoted CRI index score is also a useful marker, especially for traditional light sources, such as tungsten or fluorescent.

A Home Test

Sadly, the list of lights that have been given a TLCI score is not comprehensive, while CRI scores have limited value with LEDs. What’s more, the equipment required to undertake full BBC R&D-style analysis is not a viable option for the majority of buyers. But a quick and easy solution is close at hand.

A pocket spectroscope, available from a variety of online stores for around £30 is all you need. It can be used for fast and efficient examination of spectral composition of white light. The spectroscope consists of a metal tube with drawn out focusing, and an adjustable slit fitted with achromatic objective glass and a 3-element prism. Peer through the spectroscope and a really good light will look like this:

Poor results are easy to spot…

…but are difficult or even impossible to fix.

So a £30 investment could stop you buying an inferior light, or help you purchase a low cost option that actually performs pretty well.