What Is CRI in Lighting and Why It Matters When Buying Bulbs

You fit new LED bulbs, flick the switch, and the room looks oddly flat. Wood looks grey, skin looks sallow, and the red cushions on the sofa have gone a muddy brown. The wattage and colour temperature on the box were right, so what went wrong? Almost always the answer is CRI in lighting, the one number most buyers skip.

I specify lighting for homes and small restaurants, and CRI is the first figure I check on any bulb or fixture. It costs very little to get right and a lot of disappointment to get wrong. Here is what it measures, what values to look for, and where the number on the box can mislead you.

What CRI in lighting actually measures

CRI stands for Colour Rendering Index. It is a score from 0 to 100 that describes how accurately a light source shows the colours of objects compared with a reference light, which for warm bulbs is essentially an ideal incandescent glow and for cool bulbs is daylight.

The test shines the bulb on a set of standard colour samples and measures how far each one drifts from how it looks under the reference. The standard CRI figure, written as Ra, is the average of the first eight samples, all fairly soft pastel tones. A score of 100 means no drift at all. Old incandescent and halogen bulbs score close to 100 because they produce a smooth, continuous spectrum.

LEDs work differently. Most white LEDs are a blue chip coated in phosphor, and cheap phosphor mixes leave gaps in the spectrum, particularly in deep red. The light still looks white when you stare at the bulb, but objects lit by it lose richness.

What CRI number to buy for each room

As a rough guide, here is what I recommend to clients:

CRI	What it looks like	Where it fits
Below 80	Dull, slightly washed out, skin looks grey	Garages, sheds, outdoor security lights
80 to 85	Acceptable, most budget LEDs sit here	Hallways, utility rooms, cupboards
90 to 94	Natural, warm, wood and skin look right	Living rooms, bedrooms, dining rooms, chandeliers
95 and above	Very close to halogen	Kitchens, bathroom mirrors, artwork, wardrobes

The price difference is smaller than people expect. A standard 806 lumen E27 LED at CRI 80 costs around 2 to 4 pounds. A CRI 90 equivalent from a reputable brand is usually 4 to 8 pounds, and CRI 95 filament bulbs typically run 8 to 15 pounds. For a chandelier with six or eight candle bulbs, upgrading the whole set costs perhaps 20 to 40 pounds extra, which is a small share of what the fixture itself cost.

Why R9 matters more than the headline CRI

This is where I disagree with the usual buying advice, which says "just buy CRI 90 and you are done." That is better than nothing, but the headline Ra figure has a blind spot.

Remember that Ra averages only eight pastel samples. It does not include R9, the saturated red sample. Red is exactly where cheap LEDs are weakest, and red is what gives skin a healthy look, makes wood floors warm and keeps food appetising. A bulb can score Ra 90 and still have an R9 of 10 or even a negative number, because the manufacturer tuned the phosphor to hit the average without fixing the red gap.

So my rule is simple: look for CRI 90 or higher and R9 above 50. Good bulbs often list R9 on the packaging or the spec sheet, sometimes as "R9 greater than 50". If a brand will not publish R9, assume it is low. Our guide to reading a light fixture spec sheet shows where these figures usually hide.

How CRI interacts with colour temperature

CRI and colour temperature are separate properties, and buyers often mix them up. Colour temperature, measured in kelvin, describes whether the light itself looks warm or cool: 2700K is warm and golden, 4000K is neutral, and 5000K and above look bluish. CRI describes how faithfully that light shows other colours.

A 2700K bulb with poor CRI still looks warm, but the room looks oddly lifeless. A 4000K bulb with excellent CRI looks crisp and clean rather than clinical. In practice, poor CRI is the reason many people blame cool white bulbs for looking harsh, when the real fault is the missing red in the spectrum.

For most homes, I pair 2700K to 3000K with CRI 90 or above in living spaces, and 3000K to 4000K with CRI 95 for kitchen worktops and task areas. If you are planning task light in a kitchen, the same thinking applies to strips, as covered in planning under cabinet lighting in a kitchen.

Where high CRI makes the biggest difference

Crystal chandeliers. Crystal breaks light into small flashes of colour. A bulb with weak red output gives a dull, bluish sparkle. High CRI bulbs bring back the rainbow fire that makes crystal worth buying.
Bathroom mirrors. Applying makeup or shaving under low CRI light leads to surprises in daylight. CRI 95 is worth it here.
Kitchens. Telling whether chicken is cooked or fruit is ripe depends on seeing red and pink accurately.
Dining tables. Food looks more appetising and people look healthier in conversation. This is why good restaurants are obsessive about it.
Wardrobes and dressing areas. Navy and black, or two shades of brown, can be hard to tell apart under poor light.

In a garage or a utility cupboard, by contrast, CRI 80 is fine. Save the money for the rooms you actually spend evenings in.

A quick test before you commit

If you are unsure whether a bulb is good enough, try it before buying a full set:

Buy one bulb of the type you are considering.
Fit it in a lamp next to an old halogen or a known high CRI bulb.
Hold your hand, a red apple and a piece of wooden furniture under each in turn.
Take a phone photo of each with the white balance locked.

If your hand looks grey or the apple looks brown under the new bulb, the CRI or R9 is too low. It takes ten minutes and saves you buying eight wrong bulbs.

Frequently asked questions

Is CRI 80 good enough for a home?

For hallways, storage areas and outdoor lights, CRI 80 is acceptable. For living rooms, kitchens, bathrooms and anywhere you look at faces or food, CRI 90 or higher makes a visible difference. The extra cost per bulb is usually only a few pounds.

What is the difference between CRI and colour temperature?

Colour temperature tells you whether the light itself looks warm or cool, measured in kelvin. CRI tells you how accurately that light shows the colours of objects. A bulb can be warm and still have poor colour rendering, so check both numbers.

Do high CRI LED bulbs use more energy?

Slightly, in some cases. High CRI phosphors can be a little less efficient, so a CRI 95 bulb may need 1 or 2 more watts to produce the same lumens as a CRI 80 one. The difference on a yearly bill is very small compared with the improvement in how the room looks.