Nice concept, did you use an image with a transparent part on it?
We had quite a similliar idea
Rat Hole City
A downloadable game for Windows
In Rat Hole City you go around in tunnels and run away from buggaboos(bugs). If you touch buggaboo you die ;-;. If you get buggaboo to touch laser buggaboo turns into light. You are in the dark so you have a flash light. Your flashlight has a limited amount of power because that was the theme of ld39.
Press f4 to change between full screen and normal screen. I would recommend full screen because this accidentally became a horror game half way through and full screen would make it more spooky. Playing with the volume on is also recommended because without it the game would probably be really hard.
I'm not sure why I wrote this like I did but I feel bad about it so I'm sorry...
All of this was made in 72 hours during #ludumdare 39.