Colour Temperature Guide: From 2200K to 4000K

Colour temperature is the first colour decision in any lighting scheme and the one most visible to a client. It sets the emotional register of a space before any question of layout or output arises. This guide explains the kelvin scale, the character of the common values, how to move between them within one property, and where technologies such as dim-to-warm and tunable white earn their place.

The kelvin scale

Correlated colour temperature (CCT) is expressed in kelvin and refers to the colour of an idealised body heated to that temperature: lower numbers are warmer and more amber, higher numbers cooler and bluer. The scale runs against intuition — 2200K is warmer than 4000K — because it describes physics rather than mood. Candlelight sits near 1800–2000K, a traditional tungsten lamp around 2700K, halogen close to 3000K, and overcast daylight at 6500K and beyond. Interior architectural work lives almost entirely between 2200K and 4000K.

Character and typical uses by CCT

The differences are larger than the numbers suggest. The 300K step from 2700K to 3000K is clearly visible side by side, and the step from 3000K to 4000K changes the character of a room entirely. Note also that the same CCT can read differently on different finishes: warm light flatters timber, brass and plaster tones, while very cool light can make the same palette appear grey.

Mixing colour temperatures within one property

A whole property does not need a single CCT — it needs deliberate transitions. A common and successful pattern in London residential work is 2700K throughout the living spaces, bedrooms and circulation, with 3000K confined to enclosed task-led rooms such as utility rooms, plant areas and sometimes kitchens and bathrooms. The discipline is spatial: changes of CCT should happen at thresholds, between rooms that are not read together, never within one visual field. Where an open-plan kitchen flows into a living area, keep both at the same CCT and create difference through layout and intensity instead.

Consistency rules

• Never mix 2700K and 3000K within one sightline — on one ceiling, one run of joinery, or through a wide opening between connected spaces.
• Match CCT across fitting types in a room: downlights, joinery strip, table lamps and decorative fittings should agree, or the coolest source will look like an error.
• Specify colour tolerance (3 SDCM or tighter) as well as CCT, so that fittings marked with the same kelvin value actually match — see our guide to CRI and colour rendering for how binning works.
• Check lamp-based decorative fittings: retrofit lamps vary widely, and one 4000K lamp in a chandelier will undo an otherwise disciplined scheme.
• Record the chosen CCT for every area on the fitting schedule, so replacements years later stay consistent.

Dim-to-warm

Incandescent sources warm as they dim; standard LED does not — it simply gets dimmer at a fixed CCT, which is why deeply dimmed LED scenes can feel flat. Dim-to-warm (also sold as warm-dim) products rebuild the incandescent behaviour by shifting from around 2700–3000K at full output down towards 1800–2200K at low level. The result suits dining rooms, bathrooms used at night, bedrooms, snugs and hospitality settings where the evening register matters. Two cautions: quality of the warm end varies considerably between manufacturers, so sample before committing; and the dimming curve depends on the driver and control method, so the fitting, driver and dimmer must be selected as a set.

Tunable white

Tunable white fittings contain two or more LED channels and can be driven to any CCT across a range, typically about 2700K to 6500K. In homes the compelling uses are specific rather than general: dressing rooms that can preview clothing under evening and daylight conditions, studies and home offices that track the day, and art positions where neutrality is occasionally wanted. Tunable white doubles the control channels and adds commissioning effort, so it should be specified where the capability will genuinely be used rather than as a default — a matter to resolve early through dimming and controls coordination.

Exterior colour temperature

Outside, warmer is almost always better. 2200–2700K flatters brick, stone and planting, reads as hospitable from the street, and avoids the forensic quality that 4000K floodlighting gives a garden. There is also a wider courtesy at stake: cooler light is richer in blue wavelengths, which scatter more in the atmosphere and contribute disproportionately to sky glow, and which are more disruptive to bats, moths, birds and other nocturnal wildlife. Dark-sky guidance therefore favours warm CCTs — 2700K or below where practical — alongside proper aiming, shielding and curfew controls that switch garden lighting down late at night. In sensitive edges of London, near parkland, rivers or protected habitats, these choices may also be raised at planning.