Arm Lamp

A single counterweight
This construction uses a chain to keep the arm with the counterweight and the forearm parallel.
The lamp-cap and counterweight move in opposite directions (both away from the base or both towards it).
The balance that is required is shown by the following formula:

d1 = Lamp-cap to base; m1 = weight of lamp-cap

d2 = counterweight to base; m2 = weight of counterweight

m1 × d1 = m2 × d2 -

Lamps with povoting arm

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(6-1-3) One parallelogram with an extended counterweight
This lamp is similar to the one above, but as the counterweight has a low position, the lamp needs no heavy foot for stability: the centre of gravity is low.
The counterbalance does not swing but slides an rotate safer around the stand.

Long-arm-lamp

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Exceptional long arm lamp

Lamps with povoting arm

One Straight forearm lamp