By Emma Young
This Sunday marks the official end of British Summer Time, and once the clocks have gone back, it will of course begin to get dark even earlier in the afternoon. Now new research suggests that if you find yourself feeling uncomfortably cold as you head home from work through dimmer light, the light change itself could have something to do with it. The study, led by Giorgia Chinazzo at the Swiss Federal Institute of Technology in Lausanne and published in Scientific Reports, shows for the first time that levels of daylight affect our perceptions of temperature.
The team used a specially designed room in which the temperature could be precisely controlled, and levels of daylight independently modified, using a range of filters applied to the large windows.
A total of 84 people (42 men and 42 women) were given paper-based, office type tasks to complete at three room temperature levels — 19°C, 23°C and 27°C — and in three daylight illuminance conditions (low, medium and high). The researchers used sensors to monitor the air temperature around each participant, and also their skin temperature at various spots on their bodies.
After each 30-minute session of tasks, the participants reported on how cool or warm they felt in the room, as well as how “comfortable” and “acceptable” they considered the room temperature to be.
Some clear patterns emerged. Variations in light levels didn’t affect the participants’ actual skin temperature readings, or how cool or warm they felt the room, or various parts of their body, to be. However, when the daylight levels were low, they perceived the cooler temperatures as being more uncomfortable and less acceptable than when light levels were high. Similarly, when light levels were high, the higher temperature (27°C) was perceived as being less comfortable and acceptable than when light levels were low.
The team concludes that this is a cross-modal effect, in which perceptions in one sense influence those in another. “The findings presented here provide the first evidence that daylight can affect human subjective thermal perception from a psychological point of view and that results depend on the thermal environment to which people are exposed to,” they write.
There are various potential implications of this finding. For example, those working in office buildings that allow in plenty of daylight may require less air conditioning on hot days that are particularly cloudy, when the light levels are lower. Similarly they may need less heating on cool days that are especially bright, potentially saving energy.
Although this study involved daylight, not artificial light, it also suggests one method that might help get through the next few months of darker afternoons. If you’re feeling uncomfortably cold indoors, and you really don’t want to put on another layer, you might try turning on more lights before you reach for the thermostat.