In article ,
TKM wrote:

There were (are?) two types of socket "buttons". One type uses a diode; the
other a thermistor. The diode type cuts the power to the lamp by 1/2 which
translates to a light output reduction of 2/3. Lamp life is long to
indefinite. The lamp also flickers more and that bothers some people.

It gets a little worse than that! That 2/3 light reduction is
accompanied by a power reduction of not 50%, but more like 41-42% because
the cooler filament has reduced resistance.

- Don Klipstein )