Have you read the EBU Fact Sheet on LED lights? Why here is one we prepared earlier. The EBU suggests LED lights need to be measured and rated with the Television Lighting Consistency Index (TLCI) instead of the current CRI method which dates back to 1960.
As a modern and efficient light source for television productions, LEDs are an attractive solution. However, their introduction is leading to unintended and possibly expensive consequences of poor colour reproduction. The EBU is helping to address the issues.
Broadcasters are continually looking for more efficient technologies and thus more and more are introducing LED lighting in their studio environments. But it isn’t until the final images are seen that the problems of colour-rendering consistency become obvious.
And when a television camera captures the wrong colour it is firmly embedded in the signal; no colourist can correct all of the problems this creates.
THE CHALLENGE FOR BROADCASTERS
LEDs offer several advantages in terms of energy efficiency, light weight, their long life and the reduced need for power hungry air conditioning systems. Most EBU member broadcasters are already using these light sources in their daily production for reasons of economy.
Nevertheless, LED lighting opens the door to several problems with colorimetry or colour reproduction , resulting in reduced picture quality. As broadcast television is constantly seeking to improve picture quality (in order to maintain sales potential in a converging market), colour fidelity and consistency are important factors in these efforts.
The Macbeth ColorChecker chart on the left shows the different appearance of a set of colours under different lighting conditions
This photo on the right illustrates the impact that different LED light sources can have on skin tones.
There is only one internationally approved measurement system for the assessment of light sources, the Colour Rendering Index , which dates originally from the 1960s, and is aimed at colour rendering for the human viewer rather than the TV camera. The BBC pioneered some research with the development and proposal of a Television Lighting Consistency Index (TLCI) in the 1970s and 80s, but needed to be updated for modern camera channels.
WHAT IS THE EBU DOING?
The research on the TLCI has been taken forward by an EBU project group on LED lights. The group has produced a Recommendation on lighting measurement, R 137. A 2012 update of the TLCI was produced as part of the work, with software and supporting documentation
available for download.
Rather than assess the performance of a luminaire directly, as is done in the Colour Rendering Index, the TLCI mimics a complete television camera and display, using only those specific features of cameras and displays which affect colour performance. The TLCI is realised in practice using software rather than real television hardware. The only hardware that is required is a spectroradiometer to measure the spectral power distribution of the test luminaire, and a computer on which to run the software analysis program to perform the calculations.
Hit EBU up for more.