SM 26-70 (SM 21)

Electrical and light parameters

The rated operating point is 26 V and 70 W. Reference luminous flux is 1000 lm. 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 B15s/18. The reference envelope dimensions are approximately 57 mm overall length and 36 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

This execution is intended for aircraft luminaires and signalling units designed for a 26 V, 70 W bayonet lamp. The exact aircraft, helicopter, panel or instrument installation must still be confirmed in the applicable parts catalogue or equipment manual. Closely related SM lamps can differ in base diameter, contact arrangement and power even when their glass envelopes appear alike. Check the removed lamp and holder before ordering. The related products on this page provide navigation through the family and do not claim interchangeability.

Ordering SM 26-70 (SM 21)

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.