Manual for 2002 Trans AM says to replace DRL lights with 4157 NAK.
But both my local auto stores only carry the 4157 NA


I bought 2 and they seem to work, but whats the difference with the NAK instead of the NA?

 

http://www.donsbulbs.com/cgi-bin/r/b...~sylvania.html

I'll take a flyer and say Natural Amber Krypton. Slightly different light quality/brightness and/or lifetime?

 

$2.00

 

There are several letter designations for amber miniature bulbs that are added to the end of the bulb number:
A: Amber coated lens - a clear lens with an amber coating (not used much anymore)
NA: Natural amber - the glass of the lens is tinted amber rather than coated
NALL: Natural amber long life
NAK: Natural amber krypton

Most standard miniature bulbs are filled with an argon/nitrogen mix that helps keep the leads from arcing and the filament from burning out. Krypton filled bulbs last longer (but cost more) because it has lower heat conductivity than argon and it helps keep the tungsten of the filament from evaporating. Xenon filled bulbs are even more expensive but last even longer than Krypton.

There is no difference in light color or output between the various gas types so the NALL (long life) bulbs are perfectly acceptable as substitutes for NAK (krypton) bulbs.

 

Thank you all for the useful information. I have more to add!

When my bulb went out, I replace them with the 4157 NA (it’s all I could find locally). The bulb of course worked, but not quite right. I noticed a small delay in the flashing of the blinkers when the turn signal level was used. This was more noticeable if I was to hold the level briefly without engaging theswitch completely - like for a quick lane change.

I order a pack of 4157 NAK online, they just came in today. I've installed the NAK bulbs, and bingo - that delay before the 1st blink is gone. The flashing starts immediately just as it used to before the factory bulb burned out.

Some may say it’s my imagination, so take this for what it’s worth.

 

Krypton doesn't expand as much when heated so it doesn't push on the seals as much and ruin the light bulb by allowing air to reenter when the bulb cools. Since so little gas is put in the bulb the filament can conduct more current without bulb filament burning up. The more current run thru the skinnier the filament wire, the brighter the bulb. But the bulb also is hotter.

Argon is the standard gas used in filling light bulbs because it is cheap and it doesn't react with the hot filament. But it does expand more than krypton when heated, so the bulb will be tough on the seals from the expansion. What usually happens is the filament is made a little thicker so it has less resistance but also less light and heat. If you keep the heat down, the bulb lasts longer.

Wiki:

Krypton (along with xenon) is also used to fill incandescent lamps to reduce filament evaporation and allow higher operating temperatures to be used for the filament. A brighter light results which contains more blue than conventional lamps.