Sylvania 4257NA bulb

[Lumalux]

Does anyone have the design specs for this bulb? It is a T-6 lamp with a plastic wedge base with unusual indexing. I was able to sand down the indexing tabs and it will fit and functions properly in a socket intended for 3057/3157/3357 etc. The Sylvania packaging says it is 12.8/14.0 volts, 28.5/8.1 watts but I cannot find candlepower rating, life rating, or gas fill. I have not seen any manufacturers of this lamp other than Sylvania, leading me to think this was a one-off production for Ford for some design reason.

What is the purpose of the tubular envelope versus an S-8 globe? Is this a krypton lamp? There is less interior volume in this lamp than the usual S-8.

Luminous performance (luminescence/nigrescence, intensity) in the front signal lamps of my 2012 Toyota Avalon is not perceptibly different from the 3457s I had in there.

I emailed Sylvania for the design specs but did not get any response.

This lamp apparently is used in some recent large Ford pickups (F-150, -250, -350).

Thanks.

Alex

 

[EJR]

Looks like the 4257NA is the WT21/7W. Slightly less output than a 3157NA.

Email Daniel Stern as he likely will know the reason why Ford is exclusively using this bulb.

 

[Lumalux]

Thanks, EJR. Since the envelope is the same/similar to that used with the 7440/7443, I initially thought this might be an adaptation, but the wattages are way different.