If everyone is fixated on switching to LED or halogen lamps, so be it. For those who are still interested in the old technology, here's an extract/revision of an article that's been around on the internet for some time and seems to do a fairly good job of explaining the "old school" lamps:
LAMP (BULB) COMPARISONS:
1073 or 1141: single-filament bulb (23w). Reversing/backup lights (and single-function—brake-only, turn-only—lights).
1034: dual-filament (23/8.3w). Park/turn and brake/tail. Clear bulb for use with red rear or amber front lens.
1034A or 1034NA: Dual-filament park/turn (23w). Amber bulb for use with clear front lens.
In the early '70s, the 1073/1141 was replaced by the 1156 (single filament) (26.9w), the 1034 was replaced by the 1157 (dual filament) (27/8.3w). These 1150-series bulbs put out the same amount of light, but draw slightly more current and last quite a bit longer. When changing from 1034s to 1157s (dual filament), often it was (and is) necessary to replace the turn signal flasher, because the original would flash too fast if used with 1157s. Nowadays, it's difficult to find a flasher calibrated for 1034s.
So, what to use for upgrade bulbs? Well first, here's what NOT to use: 2057s! People sometimes assume that because it's a higher number, it's a brighter bulb. No. The difference between 1157 and 2057 is in the "minor" (dim parking or tail) filament. On the 2057, the dim filament produces 2 candlepower. On the 1157, the dim filament produces 3 candlepower. The difference doesn't sound like much, but it's very large as a percentage. Both 1157 and 2057 produce 32 candlepower from the bright (brake or turn) filament.
Though they are expensive, the best bulb you can use in place of 1157 (dual filament) is called P3496 (25.2/8.26w). It draws the same amount of current as 1157, but is much more efficient. It produces 43 candlepower on the bright (brake or turn) filament, and 3.5 candlepower on the dim (tail or parking) filament. It also has a nickel-plated base that is much more corrosion resistant than the plain brass base of an 1157.
The best replacement for 1156, 1141 and 1073 (single filament) in all applications except reversing/backup lights is P3497 (27w). It produces 45 candlepower. (Yes, the 6 and the 7 in P3496 and P3497 are reversed from the 6 and the 7 in 1156 and 1157 relative to how many filaments the bulb has. This is not a typo.) The P3496 and P3497 bulbs have a life span about double that of an 1157.
The best bulb for use in backup/reverse lights is a P796. It is a 35W halogen bulb that produces 62 candlepower, or about double the light of an 1156 and about triple the light of an 1141. The extra wattage is minor (35W vs. 28W, the wires and lenses will not notice or care) and the filament is in the right place. Neither of these compliments can be said of those 50W halogen backup bulbs you see in the parts stores! 50W is way too much current draw (100% overload!) for the stock wiring and switch, they produce way too much heat for safety near plastic lenses, and the filament's in the wrong place so the reflector doesn't work correctly with them. The P796s work great, and you finally get to see where you're going when backing at night.
