Searchlight signals display up to three different colors or "aspects" through a single lens. The internal unit has an elliptical reflector which focuses the light from a bulb through one of three colored roundels and out of the internal unit through the inner doublet lens.  The light is then focused by the outer doublet lens held by the signal case into the final beam.

The roundels within the internal mechanism are moved in and out of the light beam by a mechanism which is essentially a three position DC motor.  The armature of the motor has a counter weight on its bottom and three roundels on its top and rotates within the unit around its center.  When the mechanism is de-energized, the counterweight causes the armature to be vertical within the unit displaying the red roundel located on the armature between the yellow and green roundels. Thus, when power is lost, red, the most restrictive aspect, is displayed.  To display a yellow or green aspect, a 12 volt signal is applied to the mechanism which causes the armature and roundels to tilt approximately 13 degrees left or right within the unit until the armature encounters a stop.  This places a yellow or green roundel in the light beam depending on the polarity of the voltage applied.  A change in the polarity of the voltage causes the armature to tilt in the opposite direction placing the opposite roundel in the light beam.  The motor is connected in the rear of the unit through the two middle contacts on the bottom row.

The reflector is an elliptical shape.  With the lamp filament located at the focal point of the reflector, the reflected light is concentrated at the other focal point of the complete ellipse, which is approximately the location of the colored roundel.  Power to the light is also connected in the rear of the unit through the outer most terminals on the bottom row.  The voltage driving the light can be adjusted by the integral adjustable resistor.

Above.  Integral power resistor.  The value of the resistor is adjusted by loosening and moving the top slide from right to left.

Above.  View showing roundels and elliptical reflector which holds the bulb.

Above.  Internal view of style H housing showing the back of the prism lens and the top and side mounting hardware for the internal unit.  The mounting hardware in the H-2 unit is identical.

Closer view of the roundels.  Often the green roundel has a crack in the center from top to bottom to allow for its expansion due to the greater light absorption of the green lens.