Out association of red with heat and blue with cold is so generally accepted it is imbued in our very language. Phrases as “red hot” and through the marking of weather charts and taps all make it clear that our culture sees red as hot, and blue as cold. Strangely however, a study published in Scientific Reports reveals that when presented with objects of equal temperature we judge the blue one warmer,
Our popular representation of heat is already the reverse of physics. Blue light is higher energy than red and requires a hotter radiation source, which is why red dwarf stars are much cooler than blue giants.
However, it seems that under it all, we might intuit more physics than we think. When Dr Hsin-Ni Ho of the Nippon Telegraph and Telephone Corporation had people put their hands on lit up colored plated in a dark room that had its temperature adjusted they described the blue plate as feeling warm at a lower temperature than the red.
“I was very surprised,” says Ho. “I think as most people, our expectation is that red objects should feel warm and blue objects should feel cold.” The finding appears to be in contrast with studies that indicate that red food coloring and light shone on a false hand create greater sensations of heat than other colors.
Ho thinks this is a reaction to expectations. When you look at a red object you expect it to be warm. You have something already in your mind,” Ho says. “The contrast between the expectation and actual temperature perception will influence what you feel.”
In a second experiment Ho projected colored light onto people's hands. This reversed the results of the first test, in keeping with past studies that found red lighting makes people feel warmer than blue.
“People would tend to judge the touched object to be warmer when it is blue or when it is touched by a red hand, because the expected difference between object and hand temperatures would be smaller than the actual temperature difference,” Ho and her coauthors conclude. They also suggest the fact hands (at least for certain skin colors) get redder when hot, might have an influence on the second experiment.
The differences sound small – 0.5°C, but are larger than past experiments on room lighting. Ho compares this with changes in temperature detection thresholds over the course of a lifespan of just 0.2°C