The orbiter lighting system provides both interior and exterior lighting. The interior lighting provides illumination for display and control visibility and general flight station and crew equipment operations. Exterior lighting provides illumination for payload bay door operations, extravehicular activity, remote manipulator system operations, and stationkeeping and docking. Interior lighting consists of floodlights, panel lights, instrument lights, numeric lights and annunciator lights. Annunciator lighting is discussed with the caution and warning system. Exterior lighting consists of floodlights and spotlights.

Interior floodlights provide general illumination throughout the crew cabin and allow the flight crew to function within the flight deck, middeck, airlock and tunnel adapter (if installed). Both fluorescent and incandescent lamps are used. Emergency lighting is provided by selected fixtures that are powered via a separate power input from an essential bus.

Dual fluorescent lamp fixtures provide lighting for the mission station and payload station. The mission station lighting is controlled by an on/off switch with a rotary control switch to control brightness on panel R10. The payload station lighting is controlled by an on/off switch with a rotary control switch to control brightness on panel L9.

A single fluorescent lamp fixture is employed on each side of the commander's and pilot's forward flight deck glareshield, the commander's and pilot's side consoles and the orbit station. The commander's glareshield light is controlled by the bright, var , off switch and a dim, brt rotary control on panel O6. The dim, brt rotary control operates in conjunction with the var position. The pilot's glareshield light functions the same as the commander's, except the control is on panel O8.

The commander's side console light is controlled by an integral off/variable/on control switch. The pilot's side console light is also controlled by an integral off/variable/on control switch. The orbit station light is controlled by an on/off switch and dim, brt rotary control on panel A6.

The seat/center console floodlight has two incandescent bulbs: one illuminates the commander's lap or the center console, and the other illuminates the pilot's lap or the center console. The commander or pilot can select either the lap or center console, not both. The commander's seat or console light is controlled by the left seat/ctr cnsl flood , seat/off/ctr cnsl switch and the dim, brt rotary control on panel O6. The pilot's seat or console light is controlled by the right seat ctr cnsl flood, seat/off/ctr cnsl switch and the dim, brt rotary control on panel O8.

The middeck ceiling floodlight fixtures are located behind a translucent polycarbonate material. They are the same fixtures as those at the orbit station and are individually controlled by on/off switches on panel M013Q. The middeck panel M013Q is lighted by a small fluorescent lamp at each end of the recessed panel and is controlled by the M013Q on/off switch on the panel.

The waste management compartment floodlight is also the same as the orbit station fixture and is controlled by an on/off switch on panel ML18F.

The galley and middeck sleep station bunks (if installed) use the same floodlights as the commander's and pilot's flight deck consoles and are also controlled individually.

The airlock floodlights are similar to those at the commander's and pilot's flight deck side consoles, except they are controlled by switches on panels AW18A and M013Q.

If the tunnel adapter is installed for a Spacelab mission, the floodlights are also similar to those at the commander's and pilot's side consoles. Tunnel adapter lights 2, 3 and 4 are controlled by individual on/off switches on the tunnel adapter panel. The remaining tunnel adapter light is controlled by the tunnel adapter 1 on/off switch on panel M013Q and the on/off 1 switch on the tunnel adapter panel. The emergency floodlights are controlled by on/off switches on either panel C3 or ML18F.

Panel Lighting

Many flight deck instrument panels have integral lighting that illuminates the panel nomenclature and markings on the displays and controls. This illumination aids the flight crew in locating displays and controls while operating the orbiter. Panel lighting is transmitted from behind a panel overlay through the panel nomenclature, making it appear white-lighted. It is also transmitted to the edges of the displays and controls for general illumination. The lighting source consists of small incandescent, grain-of-wheat lamps mounted between the metal panel face and the plastic panel overlay. The overlay has a layer of white paint and a layer of gray paint on the top surface. The panel nomenclature is formed by etching the letters and symbols into the gray paint, leaving the white layer underneath. The panel, mission station and orbit station lighting is controlled by off, var, brt rotary controls on panels O6, O8, R10 and A6.

Instrument Lighting

The flight deck instruments have integral lighting that enables the flight crew to read the displayed data. Lighting is provided by incandescent lamps located behind the face of the instruments. Prisms are used to distribute the light evenly over the face. Instrument, lighting panel, and orbit station lighting are controlled by off, var, brt rotary controls on panels O6, O8 and A6.

Numeric Lighting

Six indicators on the flight deck use illuminated numeric (digital) readouts to display data. The illumination is provided by a single incandescent lamp in each segment of a digit. Seven segments are required to generate the numbers zero through nine. Each numeric indicator has a red light to indicate failures in the indicator and will be illuminated when any lamp in the indicator fails. The six numeric (digital) indicators are event time (panels F7 and A4), mission time (panels O3 and A4), RCS/OMS prplt qty (panel O3) and rri (rendezvous radar) (panel A2). The panel lighting and numeric orbit station lighting are controlled by off, var, brt rotary controls on panels O8 and A6.

Exterior Floodlights

The exterior floodlights improve visibility for the flight crew during payload bay door operations, EVA operations, RMS operations, and stationkeeping and docking. The payload bay floodlights are controlled by switches on panel A7. The RMS floodlight is also controlled on panel A7.

The payload bay floodlights are metal halide lamps that are gas discharge arc tubes similar to mercury vapor lamps. Two different fixtures are used with the lamps: one fixture mounts the floodlight on the payload bay forward bulkhead and the other fixture mounts the floodlight within the payload bay. The RMS floodlight uses an incandescent lamp. It is located near the RMS end effector.