Colour Temperature and CRI Basics

Two numbers describe most of what a buyer needs to know about a light's colour: colour temperature and colour rendering. Both are misunderstood often, and both are simple once explained. This post explains them in plain terms, without tying them to any product claim that has not been published.

Colour temperature is measured in kelvin, written as K, and it describes whether light looks warm or cool. Low numbers are warm: candlelight is near 1900K, a household warm bulb near 2700K, and warm white lighting near 3000K. Middle numbers are neutral: around 4000K feels like office lighting. High numbers are cool: daylight is near 5600K, and overcast daylight higher still. A light that adjusts from 3000K to 6000K, like the flower-shaped ring light on this site, therefore covers warm indoor evening light through to daylight.

Warm and cool are not better or worse in themselves. Warm light feels intimate and relaxed, which suits an evening stream or a beauty setting. Cool light feels clean and alert, which suits a daytime presentation or a product shot. The mistake is mixing them in one scene, so a face looks warm on one side and cold on the other. Matching colour temperature across all the lights in a scene is a small discipline that prevents that mistake.

Colour rendering is measured as CRI, or Ra, and it describes how faithfully colours look under a light compared with daylight. A CRI of 100 means colours look exactly as they do in daylight. A CRI of 95 or above is high, and suits beauty work, product photography, and any job where a buyer judges colour from a photograph. A CRI of 80 is adequate for general room lighting but poor for colour-critical work. The difference between 80 and 95 is visible in skin tones and in product colours, even to an untrained eye.

Television lighting consistency, written as TLCI, is a related measure used for video work. It describes how colours will look on camera rather than to the eye, which can differ because cameras and eyes respond to light differently. A light with both CRI and TLCI above 95, like the 40cm tube light on this site, is a safe choice for work that will be recorded as well as seen in person.

Brightness and colour are independent, and confusing them is a common error. A very bright light with poor colour rendering will make colours look wrong, however much light it gives. A dim light with excellent rendering will make colours look right, but the picture will be dark. Both figures must be checked: brightness at a stated distance, and rendering as a published value. A seller who gives only one of them is hiding the other.

Dimming interacts with colour in a way worth knowing. Some lights shift colour temperature as they dim, becoming warmer at low brightness. That shift can be pleasing for evening lighting but confusing for photography, where a consistent colour is needed at every brightness. A light that holds its colour temperature while dimming is more predictable, and a buyer who needs consistency should ask about it.

For practical buying, the checklist is short. What colour temperature range does the light cover, and does it match the rooms it will be used in? What is its colour rendering, and is it high enough for the job? Does it hold colour while dimming? And are those figures published for the exact model, rather than for a product line in general? A light that passes that checklist is unlikely to disappoint on colour, whatever its other qualities.

For beauty work, the rendering figure matters most, because a client judges the result by eye under the lamp. For product photography, rendering and consistency matter equally, because a buyer judges the product by its photograph. For video calls, colour temperature matters most, because a face that matches the room looks natural while a face that fights the room looks strange.

Finally, remember that colour numbers describe the light, not the camera. A camera's white balance setting also affects how colours are recorded, and a camera set wrongly will make even a good light look bad. Set the camera's white balance to match the light, or to automatic where the camera handles it well, and then judge the light's colour. Blaming a light for a camera setting is a common and avoidable error.

To sum up, colour temperature in kelvin tells whether light is warm or cool, colour rendering tells whether colours look true, and both must be checked together with brightness at a stated distance. Those three figures, published for the exact model, are the honest basis for comparing any two lights.

Mixed lighting is the most common colour problem in real rooms, and it is fixed by matching rather than by buying. If a room has warm ceiling lights and a daylight video light, the two will fight, and the camera will record a face that is warm on one side and cold on the other. The fix is to turn off the light that does not match, to gel it, or to set the adjustable light to the room's temperature. Matching first, and adding light second, gives a cleaner result than adding more light to a mixed scene.

Camera white balance is the second half of colour, and it is often blamed on the light by mistake. A camera set to tungsten white balance in a daylight room will record everything blue, however good the light is. A camera set to daylight balance in a warm room will record everything yellow. Setting white balance to match the light, or using automatic balance where the camera handles it well, lets the light's own colour be judged fairly.

For a buyer comparing two lights, the honest comparison uses three figures for the exact model: brightness at a stated distance, colour temperature range, and colour rendering. A light that publishes all three can be compared fairly. A light that publishes only brightness is asking to be judged on half the evidence, and a buyer should treat that gap as a reason to ask questions before ordering.

A practical test for colour rendering needs no instruments. Photograph a colour chart, a piece of fruit, and a human face under the light in question, and compare the photograph with the same subjects under daylight. If skin looks grey or green, or fruit looks dull, the rendering is poor, whatever the specification claims. That test, done once, tells a buyer more than a long specification list.

One last practical point: judge colour under the light that will be used for the work, not under showroom lighting. A light that looks good in a shop can look different in a studio, because the surrounding light changes how colours are perceived. Test in the real room, with the real background, before committing to a quantity order.