Minecraft wiki entry for Daylight_Detector, associated text: Using a daylight detector inverts it. However, the output of the inverted detector is not a simple inversion of the daylight detector's output; it uses a much simpler algorithm that depends only on the internal sky light level. Specifically, it outputs a signal strength of 15 minus the current internal sky light level, where values over 15 or below 0 are taken as 15 or 0 respectively. This means that an inverted daylight detector actually outputs a strength of 11 at midnight when it's clear weather, if it has line of sight with the sky. The effects of shade are applied before inverting, so shade increases the signal strength when it isn't already full, and prevents it from reaching zero.