Hummer H3T Dome Light Bulb Size

The Hummer H3T dome light requires a 578 bulb size for proper installation within the interior lighting housing. Data for the specified vehicle covers the 2009 to 2010 range.

The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.

Bulb Size by Year Range

Years	Bulb Size
2009-2010	578

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Festoon bulb, 41mm length, end-cap contacts. 12V, 12W.	578

Other Locations

Additional Notes

The 578 bulb is the sole dome light bulb size listed for the Hummer H3T across the 2009-2010 model years.
The 578 is classified as a festoon-type bulb, meaning it is cylindrical in shape and makes electrical contact through metal caps at each end rather than through a base socket.
The bulb operates at 12 volts and draws 12 watts, which is consistent with standard automotive interior lighting circuits.
At 41mm in length, the 578 fits within the festoon holder by compression between its two end-cap contacts, making physical length a critical factor for proper fitment.
The 578 designation follows ANSI standards recognized in both the United States and Canada, indicating a standardized specification rather than a proprietary part number.
Because festoon bulbs rely on end-cap contact pressure for both retention and electrical connection, substituting a festoon bulb of a different length risks poor contact or failure to seat correctly in the H3T dome light housing.