The headlights have two brightness settings, daytime running brightness, and night time brightness. The headlights being on during the day is for added visibility, but they're less bright than they are at night. I discovered this when I was deciphering out the RPO codes for my Cruze.
"T3W - LAMP SYSTEM - DAYTIME RUNNING, REDUCED INTENSITY LOW BEAM"
When the sensor detects low light conditions it triggers the interior illumination, reduces the dash brightness, increases the headlight brightness, and the green headlight symbol comes on.
"T3W - LAMP SYSTEM - DAYTIME RUNNING, REDUCED INTENSITY LOW BEAM"
When the sensor detects low light conditions it triggers the interior illumination, reduces the dash brightness, increases the headlight brightness, and the green headlight symbol comes on.