Looking around I have seen a lot of ideas and examples of home-made lamps built with plumbing.
I noticed that (unlike those produced professionally) very few of these lamps have an electric switch aesthetically consistent with the style(looking like a sort of valve, and if possible not only disguised as a valve but also operated like the valve) , so I tried to fill this gap.
The first idea was to find a rotary switch small enough to fit into a ball valve(1/2"),after removing the ball, and connect it to the external handle to operate. I wasn't able to find a suitable rotary switch, small enough and rated for a suitable current.
The second idea was to use a genuine valve pressing a push-button switch.
Step 1: Find the Valve
I had found a radiator valve with the valve disc(the part that regulates the flow) moving along one of the connection axis.
In this case the disc in the closed position is also close to the connection, this is good if your button is short since you don't need to put something between the disc and the button to transfer the action.
Step 2: Find the Switch
I also found a suitable push-button switch.
I put the switch in the connector(a little of sanding the switch and filing inside the connector was needed)
It is not really important whether the switch is normally open or normally closed, this will have influence only on what happens if you remove the valve pressing the button and of course on the direction the valve will turn on the light.
Being able to choose I would go for a "normally open" , BUT a "normally closed" respects the hydraulic analogy since the light is on when the water would flow through the valve and off when the valve is closed(so if your valve have some sort of <OPEN - CLOSED> indication I would suggest a normally closed switch)
this may be the right time to connect wires to the switch, or maybe not, it depends on your lamp architecture and switch position.
Step 3: Insulation Insulation Insulation!!!!
My lamp will be in 12V DC but anyway I will not economize on heat-shrink insulation to avoid shorts.
If you are considering using 220V / 125V AC BE VERY CAREFUL insulating the wires and anyway connect the pipes to the ground wire
Step 4: Screw Parts Together
Screw parts together.
add wires and test the valve can actually press the switch.