Daylight sensors output redstone level can be remapped to whatever level you want. Instead of outputting 0 at night, you can have them output 1 or 15. They can drive a redstone lamp to make a light at night. with minimal size.
Allow daylight sensors to output at night
You can re-map the output redstone level of any daylight sensor to what you want. Here is an example of a normal sensor in front, and an inverted sensor in back. Image was taken at minecraft dusk.*
You can re-map the output redstone level of any daylight sensor to what you want. Here is an example of a normal sensor in front, and an inverted sensor in back. Image was taken at minecraft noon.
