Dark Activated Emergency Light Circuit

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Whoever designed the electrical wiring in my apartment must have hated the basement. The stairway only have one light switch at the top. Also all the rooms with two doors only have a light switch on one door. That means if you were in the basement, you needed to walk up the stairs to turn the lights on. Also if you were jsut cutting through the rooms you needed to turn on the light in room A. Walk to room B, turn on the light in room B, walk to room C, turn on the light in room C, and then walk all the way back up to room A and turn off room A then B to make it into the basement.

I needed a hallway light. Being an electrical I figured I wont spend the $5 on a hallway light that blocks an outlet. Instead I'll design my own portable one that acts like emergency lighting.

This light is a monostable multivibrator circuit. It detects when the photo resistor represented by A1 transistions from light to dark. When that happens the LED D1 will turn on for a set time determined by ln(2)R2*C1.