Chevrolet Impala Dome Light Bulb Size

Additional Notes

• The Chevrolet Impala dome light specifications cover model years 1958 through 2013, with three distinct festoon bulb sizes and one bayonet-base bulb appearing across that span.
• The 578 bulb is the most consistently used type in these specifications, serving the Impala dome light across the 2000-2013 model years. It is an ANSI-standard festoon bulb rated at 12V and 12W with a 41mm length and end-cap contacts.
• The 561 bulb is the second most frequently specified type, covering the 1975-1982, 1994-1996, and 1978 model years. Like the 578, it is a 12V, 12W ANSI festoon bulb, though its length is 44mm rather than 41mm, making the two types physically non-interchangeable despite sharing the same wattage and voltage rating.
• The 211-2 bulb is specified for the 1961-1973, 1976-1977, and 1979 model years. It shares the 41mm festoon length and 12V, 12W rating with the 578 but uses an SV8.5 base rather than end-cap contacts, which means the two bulbs are not interchangeable despite their identical physical length.
• The 578 and 211-2 bulbs are both 41mm in length and identical in voltage and wattage, yet their differing base types make substitution between them a fitment concern. The 578 uses end-cap contacts while the 211-2 uses an SV8.5 base.
• The 1004 bulb is specified only for the 1958-1960 Chevrolet Impala dome light. Unlike the festoon types used in later years, it is a dual-filament bulb with a BAY15d bayonet base, rated at 12V and 21/5W, and is noted as a variant of the 1157.
• The 1004 bulb's dual-filament, higher-wattage design represents a fundamentally different construction from the single-filament festoon bulbs specified for all other Impala model years in these specifications, and the two categories are not interchangeable.
• All four bulb sizes in these specifications conform to ANSI standards applicable in both the United States and Canada.
• The transition from the 1004 bayonet-base bulb to the 211-2 festoon type occurred between the 1960 and 1961 model years, reflecting a change in dome light socket design on the Impala.
• When replacing the dome light bulb on a Chevrolet Impala, the base type is a critical fitment factor, as the 578, 561, 211-2, and 1004 each use a distinct mounting interface that is specific to the socket present in the vehicle for that model year.