Dim-to-Warm Lighting: An Experimental Analysis of Preference and Perceived Naturalness

LED luminaires that produce a shift to a lower correlated color temperature (CCT) when dimmed to mimic the dimming of an incandescent lamp are marketed as “dim-to-warm.” Despite the commercial popularity of “dim-to-warm” lighting, most academic research, to date, shows no significant preference for a reduction in CCT when lighting is dimmed. A controlled laboratory experiment was conducted where participants were exposed to a range of dynamic lighting conditions that shifted CCT as the lighting was dimmed. Participants were asked to rate each lighting condition as soon as the dimming ended, before visual adaptation was complete. Likert ratings for “preference” and “naturalness” were recorded, the experiment being repeated for work and social scenarios. The same conditions were rated using both manual and automatic dimming modes. The experiment was repeated using two different setups, a standard laboratory booth and one with participant seated in a small room and immersed in the lighting condition. Inferential statistical analysis showed that in a work scenario, any shift in CCT is less preferable and perceived as less natural than dimming with a constant CCT. In contrast, in the social scenario, a reduction in CCT close to that of an incandescent lamp was rated as similarly preferable and natural as dimming without a CCT shift. Manual dimming was preferred to automatic dimming in the immersed setup for both work and social scenarios when there was no shift in CCT. The results from this experiment provide a foundation for future research into spectral tuning of dim-to-warm lighting