The unit must always be connected to the mains via a 13A plug and socket, or some other method than can be properly isolated such as a double pole switch. Do not assume that a load is safe if it is switched off by this unit. This unit switches the neutral line, to reduce the potential difference between the circuit and earth. Also there is sufficient leakage through an untriggered triac to give a fatal electric shock. You may be able to mount the unit on a different side of the building for example.
Street lamps have the light sensor mounted on the top, above the lamp which shines downwards.
You may be able to arrange something along these lines. If you are mounting the unit outdoors you will need to arrange a suitably waterproof case. The suggested case is suitable for indoor use only. It is imperative that the circuit cannot get wet. The area where the light gets to the LDR may be difficult so seal effectively.