Canon EOS 100D Instruction Manual page 51

Switching the LCD Monitor Display
With [52: LCD auto off], you can prevent the LCD monitor from turning
off automatically (p.230).
Even when the menu screen or captured image is displayed, pressing
the shutter button will enable you to shoot immediately.
If you look through the viewfinder eyepiece while wearing sunglasses,
the LCD monitor may not turn off automatically. If this occurs, press the
<B> button to turn off the LCD monitor.
Nearby fluorescent lighting may cause the LCD monitor to turn off. If this
occurs, take the camera away from the fluorescent lighting.
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