Here’s something new, though I wouldn’t be entirely surprised if someone did this before. There’s an example below.
Edit The example was buggy, should be fixed now.
Rules Place some light sources and walls. Light sources go on grid vertices, but not on the border. Walls go on grid lines and must not touch light sources. Numbers outside the grid indicate how many light bulbs illuminate the adjacent edge in total, where a light bulb that illuminates the entire edge counts for 1 (regardless of distance), a light bulb that illuminates the edge partially counts for the corresponding fraction.
Hm, should the lowest number on the right of the example be a 3/2? 1 coming from the upper light source, 1/2 from the left one.
Yes, sorry (I added a wall to the solution instead).
Should the 1/2 clue in the example not be 3/2 instead? The leftmost bulb contributes 1/2 and top one gives full light, unless I am missing something.
You’re right. I fixed it (I hope) by placing an extra wall.