The effects of radiation from the surroundings on the impressions of freshness of 106 men and 39 women members of the staff of the Building Research Station were investigated during the first 6 months of 1948. Subjects were exposed to three types of environment: (1) where the walls were cooler than the air, (2) where the walls and air were at the same temperature, and (3) where the walls were warmer than the air. The tests were carried out in calm air.

It was found that the difference between the mean radiant temperature and the air temperature affected freshness impressions, but the effect was relatively slight. Environments which felt cool tended to feel fresh, yet a rise in the mean radiant temperature—which would increase the warmth of the environment—tended to produce an impression of greater freshness. At a given equivalent temperature, environments with the surroundings warmer than the air were found to be definitely fresher than cold- and neutral-wall environments. This was thought to be mainly due to the fact that the humidity of the air in the warm-wall environment was lower than that in the other two environments. Changes in humidity insufficient to affect sensations of warmth affect impressions of freshness. Under the conditions of these experiments, and to keep freshness impressions constant, a rise of 1° F. in the temperature of calm air must be compensated by a fall of about 5% in the relative humidity.

The subjects had a distinct preference for the warm-wall environment; 73% of them found it pleasanter than either the cold- or the neutral-wall environment.

Freshness impressions are considered to be related to transient fluctuations in the rate of heat loss from the head.