A hair color approved in the salon and disputed the next day in daylight: the problem rarely comes from the product. It comes from the light under which you and your client judged the result.
The two figures to remember: between 4,000 and 5,000 K for a salon where color is done, and especially a CRI above 90. The second matters more than the first.
What overly warm light does
At 2,700 or 3,000 K, the light is yellow. It warms everything it illuminates: an ash blonde appears golden, a cool brown turns chocolate, and the green reflections of a botched bleaching go completely unnoticed.
It's pleasant for reception and atmosphere, but it's a trap for the color station. Many salons have the good reflex of separating the two: a warm ambiance at the entrance, neutral light where work is done.
What overly cool light does
Above 6,500 K, the light tends towards blue. Complexions appear grey, blondes take on a cool reflection that doesn't exist, and the overall effect gives a clinical impression that no one wants in a salon.
This is the difference with a detailing bay, where we deliberately push towards 6,500 K: there we judge a car body, here we also judge a complexion and a mood.
Temperature chart
| Temperature | Effect on hair | Where to use it |
|---|---|---|
| 2,700 – 3,000 K | Warms everything, masks cool reflections | Reception, waiting area |
| 4,000 K | Neutral, slightly warm | Cutting and coloring stations |
| 5,000 K | Close to daylight, very accurate | Color diagnosis station |
| 6,500 K | Accurate but cool on complexions | Reserved for technical workshops |
CRI matters more than kelvins
Color temperature describes the general hue of the light. CRI describes its ability to accurately render each color. A 4,000 K lamp with a CRI of 75 will poorly render reds and coppers — precisely the most delicate shades in hair coloring.
A useful benchmark: daylight has a CRI of 100 by definition. Below 90, you won't see the same thing your client will see outside. That's why CRI is the first criterion to check on a product sheet, even before kelvins.
The display window test
There's a free and immediate test: take a treated strand of hair near the display window, in daylight, and compare it with what you see at the station. If the color changes significantly, your working light is not telling you the truth.
Do this test before buying; it will give you the measure of the problem. Do it again afterward; it will tell you if you've solved it.
Only one series of panels
If you equip the salon in several stages, use the same reference. Two different series advertised at the same color temperature almost never give exactly the same hue, and in a salon — where nuances are precisely compared — the difference is immediately visible on the ceiling as well as on the hair.
Key takeaways
- 4,000 to 5,000 K at workstations, warm light remains for reception.
- CRI above 90: this is the number one criterion for color.
- The display window test tells you in ten seconds if your light is lying.
- Only one series of panels throughout the salon.
See white hexagonal LED kits — color temperature and CRI are indicated for each configuration.
