Two Types of Sunburn in Apple Caused by High Fruit Surface (Peel) Temperature

Fig. 2. Black patch method used to intercept solar irradiance and to heat peel of attached fruit in the field. A fine thermocouple attached to a psychrometric microvoltmeter was inserted under the black patch to measure peel temperature.



Image from Plant Health Progress article:
Two Types of Sunburn in Apple Caused by High Fruit Surface (Peel) Temperature