How does correlated colour temperature in office lighting affect vigilance and error rates in controlled and field studies?

What CCT actually changes in an office

CCT describes the colour appearance of white light, measured in kelvin (K). Warm light (around 3000 K) looks yellowish; cool light (around 6500 K) looks bluish. In an office, changing CCT does not necessarily change how bright the room feels: a controlled study found that at equal wall luminance, different CCTs from 2500 to 10 000 K had no significant effect on perceived brightness [1]. That matters because any effect of CCT on vigilance or errors is unlikely to come simply from people perceiving the room as brighter.

The same study found that scene preference rose as CCT increased from 2500 K to about 4000 K, then declined substantially at higher values up to 10 000 K [1]. So the CCT that people prefer is not the coolest option, even though cool light is sometimes assumed to be more alerting.

Does cooler light make office workers more vigilant or less error-prone?

The evidence is mixed and does not support a simple rule. In one office-setting experiment, error rates showed no statistically significant difference across lighting conditions [2]. In a separate laboratory study with office workers, cool white light had the lowest mean error percentage compared with other CCTs [5]. These results point in different directions, and neither establishes that CCT is a dependable lever for reducing mistakes.

Vigilance—sustained attention to a task—has been examined under dynamic CCT changes in a controlled laboratory setting using a GO/NOGO task, but the available abstract does not state whether vigilance improved or worsened [3]. That leaves the vigilance question less settled than the error-rate question.

CCT may matter mainly in combination with illuminance

One office study suggests that the effect of CCT depends on how bright the room is. At 3000 K, response times became longer as illuminance increased; at 6500 K, response times became shorter as illuminance increased [2]. The same study found that the highest P3b amplitudes—an EEG signal related to attention—occurred at 3000 K and 750 lux, consistent with participants' subjective workload ratings [2]. The authors concluded that 3000 K at 750 lux produced the lowest mental workload, but they also noted that the interaction between CCT and illuminance was not clear [2].

This means a question like “is cool or warm light better for vigilance?” may be too simple. The answer could depend on the brightness level, and the evidence so far does not map that interaction reliably.

A caution from driving studies

A simulated night-driving study found that lower CCT was associated with longer reaction times, more errors, and greater sleepiness, while higher CCT improved contrast sensitivity [4]. That is a different task, a different environment, and a much lower light level than an office, so it should not be treated as evidence about office lighting. It does, however, illustrate that CCT effects can appear in some demanding visual settings without necessarily transferring to desk work.

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