The Ford Barn - View Single Post - FYI

MikeK · 01-30-2019, 11:06 PM

Badpuppy,

per SAE std. J573d Mar. 1918, rev. 12/68:
@6.4V (full charged lead antimony battery only@ 68F) all lamps at rated circular candlepower output were driven to 2725K:
21cp = 2.63A
32cp = 4.01A
50cp = 6.27A
____________________
@7.1V (correct generator setting to maintain full battery charge) all lamps produced 2875K averaged spectral output.
21cp(now driven [email protected]) = 2.68A
32cp(now~34cp)= 4.08A
50cp(~54cp) = 6.34A
_____________
The purpose of the original circular ridges on the top (front) of the Ford and Lincoln spec. lamps was to diffuse direct point emission from the forward 138 degrees of the lamp. That part of the light would not strike the reflector and could not be focused into the parallel beam necessary to produce the driving beam. The ridges reduced glare to oncoming traffic.

All headlamp bulbs had a L.C.L. of 1.25". This is an exact match for the 1.25" focal length of the Ford parabolic reflector. Being equal, you could focus any Model A headlamp when OFF!!! All you had to do was to look at the reflector base and make sure the top edge of the bayonet pins were flush with the crimped ring of the socket guide in the reflector.

Many pre-1932 original headlamps were in S8 (8/eighths, 1" diameter) envelopes.

S10 envelopes followed later in an attempt to decrease the concentration of vaporized tungsten deposition (blackening) as the lamp aged.

The RP envelopes followed in a further attempt to change and reduce the blackening pattern as lamp aged. You may notice many RP envelope lamps have black dots or caps (skew caps) attached. These are more effective than the ridges in reducing glare to oncoming traffic.

As a side-note here, you will notice 'modern' halogen headlamp assemblies all have mechanical caps in front of the envelopes to prevent direct line of sight.

01-30-2019, 11:06 PM	#2
MikeK Senior Member Join Date: May 2010 Location: Windy City Posts: 2,919	Re: FYI - 6 Volt Bulbs Badpuppy, per SAE std. J573d Mar. 1918, rev. 12/68: @6.4V (full charged lead antimony battery only@ 68F) all lamps at rated circular candlepower output were driven to 2725K: 21cp = 2.63A 32cp = 4.01A 50cp = 6.27A ____________________ @7.1V (correct generator setting to maintain full battery charge) all lamps produced 2875K averaged spectral output. 21cp(now driven [email protected]) = 2.68A 32cp(now~34cp)= 4.08A 50cp(~54cp) = 6.34A _____________ The purpose of the original circular ridges on the top (front) of the Ford and Lincoln spec. lamps was to diffuse direct point emission from the forward 138 degrees of the lamp. That part of the light would not strike the reflector and could not be focused into the parallel beam necessary to produce the driving beam. The ridges reduced glare to oncoming traffic. All headlamp bulbs had a L.C.L. of 1.25". This is an exact match for the 1.25" focal length of the Ford parabolic reflector. Being equal, you could focus any Model A headlamp when OFF!!! All you had to do was to look at the reflector base and make sure the top edge of the bayonet pins were flush with the crimped ring of the socket guide in the reflector. Many pre-1932 original headlamps were in S8 (8/eighths, 1" diameter) envelopes. S10 envelopes followed later in an attempt to decrease the concentration of vaporized tungsten deposition (blackening) as the lamp aged. The RP envelopes followed in a further attempt to change and reduce the blackening pattern as lamp aged. You may notice many RP envelope lamps have black dots or caps (skew caps) attached. These are more effective than the ridges in reducing glare to oncoming traffic. As a side-note here, you will notice 'modern' halogen headlamp assemblies all have mechanical caps in front of the envelopes to prevent direct line of sight.