Sometimes the light sensor goes crazy and reports 30000 lux even in a dim light because of what auto-brightness attempts to blind you in a moment. These random spikes happen when you hold a phone at certain angles and depend on light bulbs used in a room.
The fix is implemented as an Xposed module.
Basically, it is a filter inserted near a point where native HAL communicates to Android framework. It intercepts all sensor readings and replaces abnormal 30000 lux (and 0 lux following 30000) with an averaged value from a sliding window. This affects any process that use Android sensors API including system_process, so that default Android auto-brightness works fine too (no need to use apps like Lux Dash to workaround the issue).
- Download and install Xposed framework
- Then install Nexus 5 Light Sensor fix module and activate it
The module provides no user interface, nor it runs any services in a background. It only injects a proxy method to the implementation of Android sensors API. You won't be able to notice it in the main menu or in a task manager. Think of it as a patch that can be turned on and off through Xposed installer.
The mod is open source (with permissive MIT licence), the source code is available on my GitHub.