Peak draw of laser printer at start up could go to a 1000 watts for a few hundred milliseconds.
Which shuld not dim lights, unless.....
Many electrical codes permitted ac wall socket wiring where the wires are pushed into the back of the socket to make contact via small leaf spring type contacts. Then by this same method string other sockets onto the same circuit.
Given time, moisture, corrosion these become high resistance connections with predictable crappy current conduction abilities. So the light that is plugged in to the next socket will dim when a fairly high current is drawn by a device on the previous socket, creating a voltage drop to the next device (light bulb) on the same circuit.
This type of wiring is also capable of generating a fair amount of heat at the outlet, sometime resulting in fire.
Solution: pull socket out of junction box, check to see if wires are in push connector mode, move them to the screw head connection on the side, tighten and all will be well.
Old sockets frequently have bad connections even if screw connections are used. Tighten connection, or get a new socket.
My current house was wired in this manner. Go%$*&amn cheap a$$ electricians
. I replaced 4 burned sockets, then went and re wired all outlets to use the screw connections. No more weird electrical problems. And eliminated 4 fire hazards.
Reason for electricians using the the push connector method; faster install , more money made per job.