How Can You Ensure Lighting Reveals an Artwork’s True Colors?

Your high CRI lights¹ make colors look dull. This disappoints visitors and misrepresents the art. You need to look beyond just CRI to reveal the true, vibrant colors in your gallery.

To reveal an artwork's true colors, don't rely solely on a high CRI score. You must also evaluate advanced metrics like IES TM-30² (for color fidelity³ and gamut⁴) and a high R9 value⁵ (for rich reds), especially for critical pieces like portraits or ancient textiles.

I've seen many clients feel frustrated after investing in what they thought were the best lights. They chose fixtures with a CRI of 95 or higher, expecting perfection, only to find the reds looked muted or skin tones appeared unnatural. It's a common problem, but one with a clear solution. Understanding the limitations of CRI is the first step. Now, let's explore what you should be looking for instead.

Why Isn't a High CRI Score Enough for Perfect Color?

You've been told CRI is the gold standard for color quality. But relying on it alone can lead to poor results, making priceless artifacts look cheap and disappointing everyone.

A high CRI score is not enough because it's an average of only eight pastel colors, and it completely ignores strong, saturated colors like deep red. This means a light can have a 95+ CRI score but still make vibrant artwork look washed out and lifeless.

For over a decade, I've worked with museum curators who were puzzled by this exact issue. They would specify lights with a CRI of 97, yet the rich crimson in a royal garment or the warm blush on a portrait would look flat. The Color Rendering Index, or CRI, was developed a long time ago. It was a good start, but it has significant limitations for modern applications like museum lighting.

The Problem with Averages

CRI calculates an average score based on how a light source renders eight specific, muted color samples⁶. The problem is that art isn't just made of muted colors. A light source can perform well on these eight samples but poorly on others, especially deep, saturated colors.

The Missing Red

Crucially, the standard CRI calculation does not include a deep red color. This specific value, known as R9, is measured separately. Red is a vital color in art history and is essential for rendering natural skin tones. A light with a high CRI but a low R9 value will always fail to bring life to portraits and many historical textiles. For museum-quality lighting, a high R9 value⁵ (ideally above 90) is non-negotiable.

How Can TM-30 Give You a Truer Picture of Color?

You need a reliable way to judge a light's color performance. Without a better metric, you are just guessing, risking a poor presentation of your collection and wasting your budget.

TM-30 gives you a truer picture by using 99 color samples⁶, not just eight. It provides two key numbers: Fidelity Index (Rf)⁷ for color accuracy and Gamut Index (Rg)⁸ for color saturation. This dual-metric system offers a much more complete and practical evaluation.

When IES TM-30² was introduced, it was a game-changer for our work at Dothelight. Finally, we had a system that spoke the language of artists and designers, not just engineers. It helps us explain to procurement managers like Mr. Smith why one light fixture is superior to another, even if their basic CRI scores are similar. It moves the conversation from a simple number to a meaningful discussion about visual intent.

Fidelity and Gamut Explained

Think of TM-30 as giving you a two-part report on a light's performance.

• Fidelity Index (Rf)⁷: This is similar to CRI in that it measures color accuracy against a reference source. An Rf of 100 means the colors look identical. We aim for an Rf of 90 or higher.
• Gamut Index (Rg)⁸: This measures how saturated or desaturated colors appear. An Rg of 100 means the saturation is the same as the reference. A score over 100 means colors are slightly more saturated, which can make them "pop" visually.

Using Rf and Rg Together

The real power of TM-30 is looking at both values. You might want pure accuracy for a historical document, so you'd look for an Rf near 100 and an Rg near 100. For a modern abstract painting, you might prefer an Rg of 105 to make the colors feel more vivid, while still keeping a high Rf.

How Do You Apply These Metrics in Practice?

Knowing the theory is great, but you face real-world project deadlines and budgets. How do you translate these numbers into a confident purchasing decision that guarantees a stunning visual result?

In practice, you must demand a full TM-30 report and the R9 value from your supplier. Next, request a physical sample of the proposed light. Finally, test that sample directly on the most color-sensitive artworks in your space to see the results with your own eyes.

I will never forget a project for a gallery exhibiting ancient silk robes. On paper, the client's existing lights were fine—they had a CRI of 96. But the deep reds and golds looked lifeless. We brought in one of our zoomable spotlights with a high R9 and a specific TM-30 profile (Rf 94, Rg 102). When we lit the robe, the director gasped. The gold thread shimmered, and the crimson looked as rich as the day it was dyed. This is why on-site testing⁹ is the most critical step. Data sheets don't have the final say; your eyes do.

Your Practical Checklist

When I consult with a client, I walk them through a simple, three-step validation process.

1. Demand the Data: Do not accept a spec sheet¹⁰ with only a CRI value. Ask for the full IES TM-30² report (which includes Rf, Rg, and a color vector graphic) and the specific R9 value. A serious manufacturer like us will always provide this.
2. Get a Sample: Never commit to a large order without first testing a physical sample. The performance of a light can be affected by its optics and thermal management, so you need to test the final product.
3. Test in Context: Take the sample into your gallery. Shine it on your most challenging pieces—the ones with subtle skin tones, deep reds, or delicate pastels. Compare it side-by-side with your current lighting. Observe how it renders color, texture, and depth. Trust your visual judgment¹¹. This final step removes all risk and ensures you get the exact visual effect you desire.

Conclusion

To truly honor an artwork, select lights based on TM-30 and R9 values, not just CRI. Always test samples on-site to guarantee the perfect visual result for your collection.

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