Questions about CRI: Why light affects perception more than you think

We spoke with Mantas Šatkus, professor of lighting design and international consultant, to unpack why high CRI isn’t a luxury, but a baseline requirement when lighting performers on stage or in the studio. He explains how CRI affects skin tone perception, what happens when it’s lacking, and why the R9 channel is particularly crucial. We also touch on common pitfalls and practical advice—because even good fixtures can fail when CRI is misunderstood.

Why is a high CRI essential when choosing lighting fixtures for theatre and broadcast? How does it affect the final image?

This is one of the most important questions—because:

First, the human eye evolved under daylight, which has a CRI of 100. We instinctively sense when lighting is “off.” With a low CRI, the face appears greyish, sometimes with a green or muddy undertone. It loses dimensionality, warmth, and looks flat or wax-like. The result is visual discomfort. Even physiologically, it leads to faster eye fatigue, reduced focus, and degraded visual accommodation—especially under prolonged exposure.

Second, the entire scene must be lit with fixtures offering equally high CRI. Otherwise, there’s a perceptual mismatch, especially obvious in broadcast. A simple example: mix daylight sources with low-CRI LEDs, and suddenly the actor’s face is contaminated with “dirt”—unwanted hues that don’t actually exist in the physical environment.

Particularly critical is the R9 channel (among the 15 test colors used in CRI measurement). R9 measures strong, saturated red—and it directly affects how alive and natural the face appears. If R9 is weak, skin tones lose their warmth, and even with a high overall CRI score, the image feels “dead.”

How do you work with fixtures that have varying CRI levels? Do you have specific preferences depending on the scene or material?

My rule is simple: any light that touches the face must have high CRI—no compromises. This is especially true in television, where the face is the focal point of the entire frame. Background lighting is more flexible, particularly if it uses strong color. But if it’s white light—even in the background—I still prefer it to have a decent CRI to avoid color contamination through bounce or bleed.

Can you recall specific cases where low CRI negatively impacted the lighting quality or overall image?

Absolutely. There have been TV productions where low-CRI fixtures were used directly on performers’ faces. We had to compensate in post or by overcorrecting with camera settings, which made the image look sterile and over-processed—but only on screen. Live, the faces looked off—greenish or dull grey.

I’ve also seen issues with followspots using aging discharge lamps, or spot heads with poor optical design. Even modern LED fixtures can suffer from spectral gaps or color “noise.” All of this reduces image vibrancy, pollutes white balance, and makes fine tonal details harder to read—especially in close-up.

The conversation with Mantas Šatkus will continue. In the upcoming third part of the interview, we will shift from theory to practice in “Questions about hands-on experiments” — focusing on on-site lighting tests for cameras. This next chapter will explore how fixtures behave under real-world conditions, what the camera “sees” versus the human eye, and why practical trials are indispensable for professional lighting design.