After pilot noticed a seat-mounted red Emergency Escape Path light lens missing; along with the light bulb; Mechanic performs an Emergency Exit (E/E) Light Test. Three seat mounted lights illuminated extremely dimly. Mechanic finds twelve bulbs that were 12-volt type instead of the 6-volt bulbs required for E/E Battery packs on B737-800 aircraft.

Narrative

During preflight I happened to find a seat mounted; red Emergency Escape Path light lens missing; along with the bulb at seat 13D. When the Maintenance Technician arrived; he wanted to turn on the Emergency Exit lights as a check. I then noticed that three seats in business class had their seat mounted lights illuminated; but extremely dim. I also put those seats in the Logbook for repair. The Maintenance Technician advised me that the 12 bulbs for the 3 seats; were all the incorrect bulbs...we assumed the dim ones were 12 volt. The Emergency Exit light battery packs in the B737 are 6-volts; hence the dimness. Upon further reflection; I seem to remember numerous times in the past (at least half a dozen) where I have noticed during maintenance light tests for similar issues as described above; other dim lights as I witnessed on this aircraft. I am concerned as to the correct bulbs installed not just the 737 fleet; but now; I am also concerned about the legality of our Air Carrier's entire fleet of aircraft. The bulbs involved look exactly the same; and the part number on the bulbs requires a magnifying glass to view; due the tiny size of the bulbs.