Bosch Purion: backlight and brightness
The Purion has no brightness setting. Its backlight switches on together with the bike lights and cannot be adjusted separately. Nothing to configure; this guide explains what is and isn't possible.
Step by step
- Press the light button (bulb icon) on the Purion to switch the bike lights on. The display backlight comes on at the same time.
- Press the light button again to switch lights and backlight off.
- There is no brightness or contrast entry in the settings menu (hold − for 1 second to check: Trip reset, km/mi, Wheel, Version, on later firmware Language).
- If the screen looks faint in daylight, that is the reflective LCD design; it is meant to be read without backlight.
Tip: If your bike's lights are wired to be always on (common on Dutch and German bikes), the backlight is also permanently on; that is normal and uses negligible battery.
Can't find it?
A backlight that never comes on although the lights work usually means the display was replaced with the wrong variant or has a fault; the Purion has no setting that disables the backlight on its own.
Frequently asked
Can I dim the Purion backlight?
No. Backlight on/off follows the light button; there is no brightness level.
Why is the screen hard to read at dusk without lights?
The Purion LCD relies on ambient light; switch the lights on to get the backlight.
Does the backlight drain the battery?
Negligibly; the bike lights use far more than the display.
Manuals and video
- Bosch eBike Help Center: official error-code index
- Bosch eBike downloads: quick start guides and battery guide
- Bosch eBike dealer search (DiagnosticTool readout)
Other Bosch Purion guides
Bosch Purion: change the display languageBosch Purion: switch from mph to km/h (or km/h to mph)Bosch Purion: reset the trip distance and average speedBosch Purion: wheel circumference (why it's dealer-only)Bosch Purion: change assist modes (ECO, TOUR, SPORT, TURBO)Bosch Purion: pairing with a phone app (what's possible)Bosch Purion: check the software version and get a firmware updateBosch Purion: enable and use walk assistBosch Purion: turn the lights on and off, always-on lights
Still stuck? Take a photo of the display and show it to a local e-bike workshop. Bring the bike's system name (e.g. Bosch Performance Line CX) and the exact code; that saves diagnostic time and money.