A Modern Metric for a Digital World
The Television Lighting Consistency Index (TLCI) was created to address the significant shortcomings of older metrics like the Color Rendering Index (CRI). The fundamental problem with CRI is that it was designed to describe color performance for the human eye, but the digital sensors in modern cinema cameras do not ‘see’ color in the same way. A light source could have a nearly perfect CRI score but still produce unexpected and undesirable color shifts on camera—such as skin tones appearing slightly green or magenta—which then require time-consuming correction in post-production.
TLCI was introduced by the European Broadcasting Union (EBU) as a more relevant and reliable standard for the film and broadcast industries. Instead of asking ‘How does this look to a person?’, TLCI asks the more pertinent question: ‘How much work will a colorist have to do to make the colors from this light look correct?‘
The Science Behind the Score
The TLCI measurement process is far more comprehensive and relevant to digital cinematography than CRI.
- Full Spectrum Analysis: First, a spectrophotometer is used to measure the complete spectral power distribution of the light source in question.
- Broader Color Sample: Instead of CRI’s 8 pastel colors, the TLCI calculation uses the 18 standard color swatches found on a Macbeth color checker chart, which includes a much wider and more saturated range of colors, including skin tones.
- Simulated Camera: The crucial step is that the system’s software uses this spectral data to simulate how a standardized, three-chip broadcast camera would capture those 18 colors when illuminated by that light.
- Correction and Scoring: The software then calculates the amount of color correction a colorist would need to apply to the simulated camera output to make the colors perfectly accurate. The less correction needed, the higher the TLCI score. A score of 100 means no correction is required.
Interpreting TLCI in Practice
Unlike CRI, the TLCI score has a direct practical meaning for a production workflow. The EBU provides a clear guide for interpreting the results:
- TLCI 95-100: Excellent. The light can be used with confidence that colors will be accurate and require virtually no correction.
- TLCI 90-95: Good. Minor color correction may be needed, but it is easily manageable.
- TLCI 75-90: Acceptable, but the colorist will have to perform significant corrections.
- TLCI below 75: Poor. The light source has serious color deficiencies that may be difficult or impossible to fully correct in post.
The TLCI analysis even provides a ‘Colorist Advice’ chart, indicating the specific adjustments (e.g., ‘+1/4 Green, -1/2 Magenta’) needed to fix the light’s color casts. For this reason, TLCI has become the gold standard metric for Directors of Photography and gaffers when evaluating the quality of any professional lighting fixture, especially LEDs.