MIL-DTL-25866C
3.6 Housing. The housing shall be designed in such a manner as to support the light and
it may utilize as much of the base plate area as required. If the housing obstructs the mounting
holes, the light shall be so designed that the mounting holes are readily accessible when the
cover of the housing is removed.
3.7 Base plate. The design of the light shall incorporate a plate to provide a supporting
base for the housing. The light shall be such that it may be attached directly to the cabin
structural members or to a suitable bracket by means of the mounting holes in the base plate.
The mounting holes and a hole to accommodate the electrical receptacle mounted on the housing
shall be located as shown on figure 1.
3.7.1 Flight axis. The base plate shall be marked to indicate the proper positioning
alignment of the light with the flight axis of the aircraft. The light shall be indexed with respect
to the base plate.
3.8 Reflector. The light shall be provided with a suitable polished-aluminum reflector.
3.9 Lens. The light shall be provided with a white-plastic diffusing lens.
3.10 Lamp. The light shall be furnished with a single-contact miniature-flanged base,
B-3.5 bulb, 2.38 volts, 0.50 ampere, commercial, PR-2 flashlight lamp. The light shall be
provided with a spare lamp complete with lamp holder to be mounted conveniently inside the
housing. If lamp is of a type requiring continuous recharge of batteries from ship power source,
a pilot light shall indicate when power is on and recharging batteries.
3.11 Manual switch. The light shall be provided with an MS35059-21 switch. The
positive terminal of the self-contained battery power supply shall be attached to the center (OFF)
terminal of this switch. One of the ON terminals shall be connected directly to the lamp. The
circuit from the second ON terminal shall pass through the set of normally closed contacts of the
power failure relay, and thence to the lamp. When the switch is in this second ON position, the
light shall then be armed for automatic operation by the power failure relay. The switch shall be
located either in the light housing or external to the housing.
3.12 Inertia switch. The light shall be provided with an inertia switch, which will
automatically energize the light when subjected to a deceleration of 2 ±0.5 gravity (G). The
direction of maximum sensitivity (minimum impact force required to energize the light) shall be
as marked on the base plate. The inertia switch shall be so designed that the light will not come
on when subjected to incident vibration as encountered in aircraft. If the inertia switch is of the
maintained contact type, it shall incorporate a push button, mechanical reset device so that the
light may quickly be rearmed for automatic operation. If the inertia switch is comprised of a
momentary contact device in conjunction with a holding relay, a single circuit, normally closed
push-type switch may be utilized as a means of breaking the circuit of the holding relay in order
to rearm the light for automatic operation. The switch shall be located either in the light housing
or external to the housing.
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