Characteristics of incandescent lamps

The current taken by an incandescent lamp is purely resistive. Because of this, there is no
adverse effect on the circuit power factor and no special consideration has to be given to
the switches used. The situation is different for most of the other types of lamp.
The heat given off by incandescent lamps, especially the larger sizes, must be taken
into account in both the design of luminaires for incandescent lamps and in the selection
of luminaires for a lighting scheme. The luminaires must allow enough natural ventilation
to keep the normal working temperature of the luminaires and wiring reasonably low.

This is particularly important where luminaires are made of plastics with softening
temperatures in the region of 60°C. In such cases, the maximum size of bulb which may
be used in a luminaire is limited not by the physical dimensions of the luminaire but by
the heat generated.
When incandescent lamps are used for stage lighting or for special effects they can be
dimmed by the insertion of a thyristor control circuit. This affords an efficient way of
gradual and continuous dimming.
Voltage control units with thyristor circuits can be made sufficiently compact to be
incorporated in a light switch. Combined switch and dimmer units of this type are used
where variable light effects are required in places like hotels and housing.