(1) Where are you planning to install these lights? From the instructions it is obvious that they are for use inside a house - and not in a bathroom in the house. Certainly not for inside a greenhouse which would probably blow away both the moisture and temperature constraints. (2) If you are installing them inside a house, why do you need a plug and socket instead of wiring them into the main lighting circuit? So you can only use in spring, and store for the rest of the year?
I have read your previous thread about lack of sunlight, which also implies lack of domestic lighting.
I am guessing that you are building some form of light box for use inside the house to bring on seedlings?
From reading the instructions posted, as long as you follow the fitting requirements i.e to a non-flammable, non-electrically-conductive surface and make sure that it is earthed then connecting to a plug (with a suitable fuse) should be fine.
I am a little concerned that because (I am presuming) they will be used for raising seedlings that they will be in a humid environment (which seedlings normally like) which may exceed the IP20 rating.
I have cross-posted this to uk.d-i-y for the serious electricians to cross check (please).
HTH Dave R