What does the unit "sone" measure?

The unit "sone" is specifically used to measure the perceived loudness of sound as perceived by the human ear. It is a quantifiable way to express how loud a sound seems to a listener, making it particularly useful in fields such as acoustics and sound engineering where understanding human perception of sound intensity is crucial.

A sone is defined such that a sound that is perceived to be twice as loud as a reference sound of 40 phons (a unit related to the pitch of sound) is measured as 2 sones. This helps in creating a standardized measurement because loudness perception can vary significantly from one individual to another.

In contrast, other units mentioned in the options relate to different physical properties; frequency of sound waves relates to pitch, intensity of light pertains to brightness, and temperature of heat sources pertains to thermal energy. Thus, the measurement of loudness through sones is a distinctive parameter that reflects how we experience sound.