What Does This Error Mean?

A Kobo backlight that does not turn on is usually set to 0% brightness or the ComfortLight toggle is off. Swipe down from the top of the screen and drag the brightness slider up. If the backlight still does not appear, a soft restart usually restores it.

Affected Models

Kobo Libra 2
Kobo Sage
Kobo Clara 2E
Kobo Nia
Kobo Libra H2O
Kobo Forma

Common Causes

Brightness slider set to 0% in the quick settings menu
ComfortLight Pro schedule set to 0% at current time
Software glitch preventing the backlight driver from activating
Battery very low — backlight draws significant power and may be suppressed
Backlight LED hardware failure (less common — usually affects older units)

How to Fix It

Adjust the brightness slider.

Swipe down from the top of the Kobo screen to open the notification/settings panel. Look for the brightness slider and drag it to a higher value. Also check if ComfortLight Pro is enabled — it schedules automatic brightness reduction and can set brightness to 0% at certain times.
Check the ComfortLight Pro schedule.

Go to Settings > Reading > ComfortLight Pro. If a schedule is active that reduces brightness to 0% during the current time of day, either adjust the schedule or disable ComfortLight Pro temporarily.
Restart the Kobo.

Hold the power button for 1 second until the power options menu appears. Tap Restart. A restart reinitialises the display driver, which often restores the backlight when a software glitch is the cause.
Charge the Kobo fully.

A low battery can cause the Kobo to suppress the backlight as a power-saving measure. Charge the device to 100% and then test the backlight at full brightness.
Factory reset as a last software test.

Go to Settings > Device Information > Factory Reset. A factory reset clears all user data and returns the firmware to defaults. If the backlight works after a factory reset, a corrupted user setting was suppressing it. Re-sync your Kobo account to restore library content.

When to Call a Professional

If brightness is at 100%, the device is fully charged, and no light is visible in a dark room after a factory reset, the backlight LEDs have likely failed and the device needs repair.