CCT

Correlated Colour Temperature (CCT) is measured in Kelvin (K) and describes how warm (red) or cool (blue) the light from a light source or luminaire appears.

Lower CCTs for example 2200K will appear warmer than higher CCTs of for example 5000K which will appear cooler, crisper or even a little bluer. 3000K is most commonly specified as a more neutral white for architectural lighting applications. Warmer colours are increasingly used in some exterior applications as some evidence suggests they may be more appropriate when considering impact on fauna, it is also used in night time relaxed venues such as restaurants. Cooler colours like 4000K might be used in schools or hospitals for a cleaner, more crisp feel.

Those examples taken aside, CCT choice can be very subjective and is certainly something to consider alongside application and desired feel. It is also worth considering that LED light sources tend to have a higher efficacy in the cooler CCTs (higher Kelvin values) and this can present energy saving options where quality and feel in the lit environment may be less important for the application.

It may be logical to assume that two light sources marked as having the same CCT from two different light source manufacturers would produce light that looked the same. In practice this isn't often achieved due to a combination of complex issues such as  LED binning, thermal management, phosphor mixes, whether sitting above or below the Black Body Locus (BBL). It is good practice to try to use common light source brands across products in the same space and assess samples next to one another.

The CCT of a luminaire can shift slightly over time as LED phosphors age/degrade.

Stoane Lighting can offer samples in desired CCTs to facilitate subjective testing and evaluation for the intended function.

We offer a number of fixed CCT options in our products to allow flexibility of choice at the specification stage. In some cases, tuneable white sources can be used such that the CCT can be tuned without the need to change the light source.

Tuneable white

Fixed white light sources have a single CCT and you can select which you want. Tuneable white light sources will state a CCT range.

Whilst in principal the results are quite simple, the methods to achieve this are varied. At the most basic, tuneable white is derived by using two fixed CCTs at either end of the CCT range stated, these are mixed in relative proportions to achieve CCTs in between. Two CCT options will deliver a CCT range that doesn’t necessarily follow the BBL closely. Some systems use three CCTs to help with that issue and some even use up to fifteen CCTs and chips including colours such as cyan.

The more complicated options with more CCTs/colours to mix can require more complicated systems and LED drivers to manage them but they can also offer BBL following CCT adjustment and adjustment above or below BBL for other effects.