[screen_name]

well, since there is only two possible flags, on or off, i just use variables 0 and 1

take the current status of the light, lets say off (off=0) and then just take the absolute value of the status -1, so
0-1 = -1
|-1| = 1

turns from off (0), to on (1)

same way around
1-1 = 0
|0| = 0

turns from on (1), to off (0)