The two essential numbers for any lighting proposal

A two-Michelin-star French restaurant in Shanghai called me a few years ago with a problem nobody in the building could name. The kitchen was excellent, and everyone involved knew it. But the business was unstable, and the second-floor bar was the worst of it. Guests would eat, then leave without ordering a drink upstairs. The owner assumed it was the food, or the service, or the wrong crowd.

But it was none of those things: It was the lighting.

Specifically, the light rendered red badly enough that a beautifully plated dish came out slightly grey by the time it reached the table, and a glass of wine upstairs looked flat rather than refreshing. The kitchen had done its job, but the dining room ambience was undoing it. There’s an order to things that most people don’t notice but subconsciously do: you’ll see a plate before you smell it, and you smell it before you taste it. If the first step fails, the other two will never get a fair chance.

In a previous article, I wrote about the four questions to run through any lighting proposal before you sign off: how it balances atmosphere against fixtures, how it layers, whether colour temperature stays consistent from room to room, and how it treats materials. But there’s another question: have you checked the CRI or TM-30 scores of your fixtures?

What CRI and R9 actually measure

CRI is the number most people have heard of, usually printed on a light bulb box as something like Ra 80 or Ra 90. It's an average score built from how a fixture renders a shortlist of pastel reference colours, measured against daylight. The problem is that deep, saturated red isn't part of that shortlist. It's measured separately, as an extended value called R9, and it's often the first thing to collapse even on a fixture with a perfectly respectable average CRI. A restaurant with meat, wine, sauces and skin tones under its lights usually leans on R9, even if it’s been specified or not.

TM-30 is the newer standard built to close that gap. Instead of a narrow shortlist averaged into one figure, it tests a fixture against a much wider spread of reference colours and reports how closely that fixture tracks real sunlight. It's the best thing the industry has introduced to help guide lighting and interior designers to find the most appropriate fixture for a space, which is exactly why it's still mostly confined to the top tier of fixtures. Most manufacturers haven't implemented the TM-30 standards in their products just yet.

Why the number never makes it onto the page

Most architects and interior designers I work with still confuse CRI with colour temperature, the warm or cool tone of a light, which is a completely different measurement. This isn't a knock on anyone's competence, but a reality: spec sheets will highlight colour temperature but bury (or sometimes omit) CRI and R9 entirely, because manufacturers know most buyers won't ask.

Even on projects large enough to justify finding TM-30 data, I'm often the one requesting it directly from the manufacturer, because it still isn't standard on a spec sheet. It's a recognised global standard, but it just isn't a popular one yet, and until it is, the responsibility for asking sits with whoever is reviewing the proposal, not with whoever wrote it.

Just to recap: CCT/Colour Temperature (measured in Kelvin, K) shows the visual appearance of light. TM-30 measures the colour fidelity, saturation, and accuracy.

What to ask before you sign off

Call it the red gap, the space between what a fixture's average CRI promises and what actually happens to red once food, wine or skin is under it in the room. Closing that gap doesn't cost what people assume. On most projects, the price difference between a high CRI fixture and a low CRI one is small next to what gets spent on furniture and finishes, and it's arguably the best return on investment in the entire room, because it allows everything else to look the way it was designed to look.

Before signing off on a proposal, ask the supplier to share both the CRI rating and the R9 value for each fixture, not just the colour temperature. If TM-30 data exists, ask for it, particularly on anything where visual value matters: retail, hospitality, a showroom, a home kitchen. But this doesn’t only matter at the top end. A budget restaurant has fewer other things doing the persuading, which makes the lighting that makes the food look good even more important, not less.

A few questions I still get asked

Does every manufacturer report R9? No. Some higher-end manufacturers list it alongside CRI, but plenty leave it off entirely, usually because the fixture wouldn't perform well on that number and it's simpler not to mention it.

How much more does a high CRI, high R9 fixture actually cost? In the US, you’ll get standard, or low-CRI bulbs for $1 to $2. High-CRI bulbs will cost anywhere from $3.50 to $20 (depending on the speciality, brand, and need). While it might sound like a lot, on most projects the gap is small relative to the rest of the budget, especially compared to furniture and custom finishes. It's one of the cheapest decisions in a proposal with one of the biggest visual payoffs.

Is this only relevant for hospitality projects? No. It’s worth it anywhere visual value drives the outcome: retail, showrooms, residential kitchens and dining rooms – all benefit from the same scrutiny.

About the author

Jimmy Chu is a lighting designer with 15 years of experience leading AECOLIGHT, an award-winning lighting design agency. He is the founder of CHUBIC, which helps architects and interior designers make confident lighting decisions that better match their original design intent.