Why do OLED (Organic LED) displays dim over time?

OLED makes great contrast but its lifespan is highly dependent on user application: power on hours, contrasts settings, storage environment and operating environment.

The less time the screen stays on, the longer its lifespan.
The more intense the brightness, the shorter the display’s lifespan. Choose medium/low brightness to extend the lifespan of the OLED display.
Exposure to UV light without powering on will also cause the OLED display to degrade. Hence, by storing your handheld digital multimeter in a covered bag/case when not in use will also extend the lifespan of the OLED display.