This widget filters the world to look like it is nighttime, and gives most units searchlights. Somewhat performance-intensive due to my lack of GL-fu.
Download from caspring at the bottom of the page here.

Versions
1.5.4
- Tweaked searchlight upwards. Hopefully this is the end of the crotch light problem.
- Fixed bug where extra upward-pointing cones would appear for units going down slopes.
- "/luaui night_simplebase" replaced with "/luaui night_basetype [0-2]", with 0 = no base, 1 = simple base, 2 = full base (default)
- I hereby release this widget under the GNU LGPL, version 2.1 or later.
- Now uses color map with sunrise, sunset.
- Made searchlights stronger, not all turn on/off at the same time.
- Made days longer.
- Added day/night cycle; "/luaui night_cycle" to stop.
- Darkened default night color.
- First forum release.
- "/luaui night_preunit" to toggle whether the filtering is done before or after units and projectiles are drawn. Unfortunately, I don't know of a way to do it after units but before projectiles.
- "/luaui night_basetype" to set the base type.
- "/luaui night_beam" to toggle the searchlight beam.
- "/luaui night_setsearchlight [number]" to set the strength of the searchlight, typically 0-1, or <= 0 to turn the searchlight off.
- "/luaui night_cycle" to start/stop the day/night cycle.