Detect closed shutter I want to controll some ambient lights in my living room.

Therefore, I got some 433mhz outlets which can be turned on or off with an remote, a 433mhz transmitter and receiver on the arduino.

The arduino receives the remotes signals and knows which lamp has which state and will turn any lamp off at specific times.

Now I want to turn on the lights automatically when I close the shutter, but I have no idea how I could do this.

A light sensor behind the window won't do the job. I don't want to turn on the lights when it get's dark, but when the shuhtter get's closed.

Edit:
What came to my mind first was an light sensor inside the window, facing outside, and a IR LED. I'd attach some tinfoil to the inside of the shutter to return the IR light, which the sensor will notice. But maybe the're are some simpler solutions? Also, the tinfoil would fall off quickly...
I would go for a normally open read switch (should cost >$0.1) and a magnet on the shutter (again should cost >$0.1).  There are formulas to work out the distance that the reed switch will operate at, and it depends on the magnet, but the common ones are about 40mm.
(If you can wait 2 weeks for delivery you can get the parts off AliExpress.com)