Why does the LED display turn off while the sleep timer is active?
The LED display will turn off after 10 seconds of inactivity when the sleep timer is on — this is a power saving feature and avoids light interference at night. Press any button other than the Standby ON/OFF to reactivate the display. Do not press the Standby ON/OFF button, as this will turn the machine and the sleep timer off. (Page 8)
From the official Dyson Pure Cool AM11 Air Purifier manual, page 8
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