One would assume that a hotel which hosts business conventions would have a desk AND a desk lamp for the attendees to perform their business activities--this is rarely the case.
[Re room lighting: for a few of the hotels I've stayed at, there was so little room lighting, so they provided seeing eye dogs to guide you through your room.]
I've never been in a hotel room where the lighting was bad. What would make you need a desk lamp specifically? Also, most hotels have desks in the room. You can easily research this before booking.