The invention includes a thermometer with a backlight and a method for lighting the backlight. The thermometer has temperature sensing tip, a processor taking temperature readings and determining a sensed temperature reading of the living being from the temperature sensing tip. The thermometer also includes a display and a backlight for lighting the display. The backlight is activated upon a command from the processor and the processor determines whether to activate the backlight based upon the temperature readings. The method embodiment can includes the steps of using the processor to monitor a temperature change indicated by a temperature sensing element. The processor then detects a temperature decrease and activates a first color light emitting element to backlight a display if the temperature decrease exceeds or equals a predetermined threshold. The thermometer is operable in one of a plurality of selectable operating modes, and the predetermined threshold is dependent upon the selected operating mode. For example, operating modes may depend on patient age range or measurement location. Age range may include infant, toddler and adult.