The device application circuit works as shown in Figure 3. It can be used for warehouse, office or other places for the door light. When the permanent magnet ZT and the reed switch AG are in close proximity, the two contact pieces in the AG are disconnected due to the action of magnetic lines of force, and no voltage is applied to the ④ end of the controller DM. No current flows in the illuminating lamp H, so the lamp H is turned off. Once the door is open, the controller DM is on and H lights up.

Due to the strong light during the day, the internal resistance of the photoresistor RG is small, even if the AG is closed, R and RG partial pressure is less than 1.6V, so open the door during the day, H is not lit. Equivalent to RG bipolar open night, so the controller DM ④ terminal voltage is higher than 1.6V, H light. RG available MG45-32 non-sealed photoresistor, AG can be used for Φ3-4mm reed switch (normally closed type).