Colour rendering and colour temperature

The short answer

Colour rendering describes how faithfully light shows the colours of objects. For most cleanroom work, CRI above 80 meets EN 12464-1. Choose CRI 90 to 95 where people inspect products, judge colour or look at skin and tissue: visual inspection of vials and tablets, colour checks, operating theatres. Check R9 (saturated red) as well as the headline figure. For colour temperature, 4000 K is the usual choice in production and clinical areas, with 3000 K for rooms where a warmer feel matters more than inspection.

What CRI (Ra) means

The colour rendering index (CRI), written Ra in European standards, compares how a light source renders a set of test colours against a reference source of the same colour temperature. A score of 100 matches the reference.

• Ra is the average of eight pastel test colours (R1 to R8).
• It doesn’t include saturated colours. A light can score Ra 82 and still render strong reds poorly.
• Manufacturers usually state minimums, such as “CRI > 80” or “CRI > 95”.

Ra	What it suits
80 or above	General work, production areas, corridors and support rooms. The minimum EN 12464-1 sets for most indoor workplaces.
90 or above	Colour inspection, laboratories doing visual assessment, operating theatres and treatment rooms.
95 or above	Colour-critical inspection, clinical areas where tissue colour matters, and work where small colour differences must be seen.

R9 and the special indices

Beyond R1 to R8, there are further test colours. Two matter most in clean areas:

• R9, saturated red. LED light can be weak in deep red. A low R9 makes blood, tissue, red labels and some product colours look dull or brownish. For theatres and colour inspection, look for a positive and preferably high R9.
• R13, light skin tone. Relevant wherever people’s skin colour is assessed, such as in theatres and treatment rooms.

Some of our high-CRI luminaires state high R9 and R13 values. We quote what the manufacturer publishes and can send the full colour rendering data where it is available.

You may also see TM-30 values (fidelity Rf and gamut Rg). They give a fuller picture than CRI, but CRI remains the figure most specifications and standards use.

Why higher CRI helps in clean areas

• Visual inspection. Operators checking vials, ampoules, tablets, packaging or wafers rely on seeing small differences in colour and surface. Better colour rendering makes defects, discolouration and particles easier to spot.
• Colour-critical checks. EN 12464-1 asks for Ra 90 for colour inspection tasks.
• Clinical work. EN 12464-1 also asks for Ra 90 in operating theatres. Surgeons and theatre staff judge tissue and blood by colour, so R9 matters too.
• Comparing samples. Where colour is compared against a standard, use a dedicated colour assessment cabinet as well as good room lighting. Room lighting alone isn’t a calibrated viewing condition.

Higher CRI usually costs a little efficiency. Use it where the task needs it, and standard CRI elsewhere.

Choosing a colour temperature

Colour temperature, in kelvin (K), describes how warm or cool white light looks.

CCT	Appearance	Typical use
3000 K	Warm white	Laboratories and support rooms where a calmer feel is wanted, some hospital areas
4000 K	Neutral white	Most production cleanrooms, laboratories, food processing and operating theatres
5000–6500 K	Cool white to daylight	Some colour inspection tasks, where specified by the process

Keep one colour temperature throughout a suite of rooms where people move between them, so colour judgements stay consistent. Most of our cleanroom luminaires come in 3000 K or 4000 K. Some high-CRI versions are 4000 K only.

Yellow light is a special case. Photolithography areas in semiconductor and electronics work use yellow light with no short-wavelength (blue and UV) content, so that photoresists aren’t exposed. Some of our linear luminaires have yellow-light versions for this. Confirm the wavelength cut-off your process needs.

Flicker, briefly

LED drivers can make light flicker or cause a stroboscopic effect, where moving or rotating objects appear to slow or stop. This matters around centrifuges, mixers and other rotating machinery, and for comfort over long shifts. In the EU, ecodesign rules (Regulation (EU) 2019/2020) set limits for mains-voltage light sources on visible flicker (Pst LM) and stroboscopic effect (SVM). Ask for the driver’s flicker data, and check dimmed performance as well as full output if you’ll be dimming.

How we can help

Tell us the tasks in each room, especially inspection and colour-critical work, and we’ll suggest CRI and colour temperature to match. Start a project.

Sources: EN 12464-1:2021, Light and lighting, Lighting of work places, Part 1: Indoor work places; CIE 13.3, Method of measuring and specifying colour rendering properties of light sources; ANSI/IES TM-30; Commission Regulation (EU) 2019/2020 (ecodesign requirements for light sources).