SM 26-25 (SM 18)

Electrical and light parameters

The rated operating point is 26 V and 25 W. Reference luminous flux is 362 lm. The published average operating life is 125 hours under the stated test conditions. These values describe the lamp itself; the brightness obtained in a panel, annunciator or luminaire also depends on the optical system and supply voltage. Operation above the rated voltage increases filament temperature and can sharply reduce service life. Select the rating from the equipment circuit, not from an approximate visual comparison of brightness.

Construction and installation

The clear glass envelope contains a mechanically supported tungsten filament. This execution uses a full-size miniature bayonet base, identified as B15d/18. The reference envelope dimensions are approximately 51 mm overall length and 26 mm maximum diameter. Before fitting, compare the holder, contact arrangement, available clearance and lamp seating. Do not force the glass envelope or modify the original socket to accept a different base.

Application and correct selection

SM-series lamps are used for internal illumination and signalling where compact size and resistance to aircraft vibration are required. Installation on a particular aircraft, helicopter, panel or instrument must be confirmed in the applicable illustrated parts catalogue or equipment documentation. Related SM lamps shown on this page are useful for navigation through the family and do not indicate interchangeability. When a passport or package label is available, compare every character, suffix and separator in the designation.

Ordering SM 26-25 (SM 18)

For a supply enquiry, state the full designation, required quantity, voltage, base or holder type and the marking of the lamp being replaced. A clear photograph of the removed lamp helps verify its contact arrangement. The minimum order quantity is shown in the product attributes. Other aircraft bulbs are available in the Aircraft Lamps category. General background is available in Aircraft lighting.