http://www.electrixtask.com/model_7268.htm
incandescent
33″ Reach Clamp
lamp with Compression springs in the arms.One spring puts pull force on the blue arm.
(If the blue arm is tilted back the second spring on this arm gets push force.) The blue arm controls the two parallel arms (red) that make up the upper arm.
The other spring puts pull force on the other blue arm.
This arm controls the forearm (magenta). The two springs can be the same size; one spring has to lift more weight but is more vertical.
The other spring lifts less weight but is more horizontal.
Lamps with povoting arm
One StragIht forearm lamp
Ikea lamp
Lamp with Compression springs near the footThe Roller chain cable connects this arm parallel to the forearm (yellow).
The longer spring controls the (blue) arm.
The body (red) can turn in the horizontal plane.
The body is connected to a heavy stable foot.
The body can be smaller because the pressure springs can protrude below the body.