Headlight Visors...

Discussion in 'General Steam' started by TAG1014, Feb 13, 2018.

  1. TAG1014

    TAG1014 Frisco.org Supporter Frisco.org Supporter

    I know this has been covered before, BUT why did Frisco (and some other, but not all railroads') steam engines have headlight visors? Hold on-- before anyone starts to mention World War II blackouts (Frisco steam had headlight visors in the 1930's), so it must have been some other reason. Any ideas??

    Thanks, Tom G.
     
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  2. klrwhizkid

    klrwhizkid Administrator Staff Member Administrator Frisco.org Supporter

    Visors would reflect any upward tangential light from the reflectors back down toward the tracks, increasing the effectiveness of the headlamp. In somewhat of an inverse, most of the cab-mounted headlight assemblies on diesels had visors on the lower have of the individual headlights to prevent light from spilling onto the nose of a low nose locomotive.
     
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  3. William Jackson

    William Jackson Bill Jackson Frisco.org Supporter

    Just a thought, at times they would " Dim " the headlight showing a meet or clear of the main. Not sure how they did that with a Steam Engine.
     
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  4. gjslsffan

    gjslsffan Staff Member Staff Member Frisco.org Supporter

    I would agree that it was based on focusing the beam. It was a bonus that it just looks cool.
     
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  5. Karl

    Karl 2008 Engineer of the Year Frisco.org Supporter

    As Keith stated, visors were placed over headlamps to reflect light downward which helped to reduce glare. The story behind head lamp reflectors and visors is mathematical, and it has to do with conic sections, and in particular parabolas.

    Parabolas are quadratic function, which may be written have the formula:

    Y=ax^2+bx+c; it also may be written in vortex form as f(x)=a(x-h)^2 +k

    If one rotates a parabola, he will create the shell of a parabolic cone, which has some interesting properties. When a source (light, sound, etc) is placed at the focus of the parabolic cone, the light in this case, will strike the cone, and will be reflected out of the cone as a beam. This of course is a very desirable property. Parabolas are also useful as receivers.

    As can be seen in the attached diagram, not all the light from the source is reflected off the parabolic reflector, and it escapes or spills from the head lamp. If a visor is placed over the head lamp two things occur.

    1. The spilled light, which causes some of the “glare”, is blocked, and

    2. It is reflected downward in front of the locomotive, thus supplementing the far-reaching beam of light with illumination downward and directly in front of the locomotive.

    As Ken would say, “Isn’t math great?”



    headlamp.jpg
     
    Last edited: Feb 14, 2018
  6. frisco1522

    frisco1522 Staff Member Staff Member

    There is a headlight switch above the engineer's side window. It has 2 settings, full on and dim. The dim was taken care of by routing the electric through a big resistor on top of the switch. Also controlled the back up light and the classification lights. There's a small pull switch on bottom for the class lights. 1522 HL switch.jpg
     
  7. klrwhizkid

    klrwhizkid Administrator Staff Member Administrator Frisco.org Supporter

    Thanks, Karl, nicely done and illustrated. When you do it, it comes off as cool. In my past vocation as a training instructor, I would end such an edifying series with the ending, "And now you know the rest of the story..."
     
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  8. TAG1014

    TAG1014 Frisco.org Supporter Frisco.org Supporter

    A lot of science in this thread, but it doesn't really explain anything about all the railroads that didn't put visors on their headlights?? New York Central comes to mind as one which didn't use visors.

    Tom G.
     
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  9. meteor910

    meteor910 2009 Engineer of the Year Staff Member Frisco.org Supporter

    I love Professor Brand's detailed explanations. Outstanding! Yes, math is great!

    Regarding Tom's point - yes, several roads ran without visors on their headlights, back-up lights, etc. PRR, the great "standard RR", for example. I'd suggest they either didn't worry about the effects of not having a visor, or perhaps they aimed the lamp with a slight downward bias, or maybe used some sort of a focusing lens on the lamps. I dunno. I just looked at a photo of a PRR K4s Pacific ..... no visor, looks like the lamp shines straight ahead (but it's hard to tell specifically), and the front glass on the headlamp looks to be flat.
    K
     
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  10. klrwhizkid

    klrwhizkid Administrator Staff Member Administrator Frisco.org Supporter

    Tom, the other railroads were not as enlightened! (Pardon the pun).
     
  11. Karl

    Karl 2008 Engineer of the Year Frisco.org Supporter


    That wasn't your initial question
     
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  12. WindsorSpring

    WindsorSpring Member Frisco.org Supporter

    I wonder if visors were more common in the west or southwest. As noted above, PRR did not use them. Neither did Reading, B&O or SAL use visors. The SAL sold 2-6-6-4 articulated locomotives to B&O and it seems neither before, nor after the sale, did those locomotives have headlight visors. Later (after 1935?) C&O locomotives seemed to have short visors, but early photos, even of the same class, did not seem to have them.
     
  13. klrwhizkid

    klrwhizkid Administrator Staff Member Administrator Frisco.org Supporter

    The key point I see is that visors would increase the efficiency of the headlights by directly the light where it is truly needed, forward and downward. My answer, "the other railroads were not as enlightened", was witty but also to point out that the use of a visor was done due to an educated, rational approach that used a superior thought process as we would expect from the Frisco and so aptly illustrated by Karl.
     
  14. frisco1522

    frisco1522 Staff Member Staff Member

    The headlight beam is adjustable. The bulb socket has adjustments forward and backward and you can "fine tune" the light beam. I'm thinking the goal was to be able to see a man on the tracks at 800'. Don't hold me to that.
     
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  15. William Jackson

    William Jackson Bill Jackson Frisco.org Supporter

    Tom maybe you didn't look at my post. Forget all the math stuff. The reason is rules that train's must dimm their headlights under certain condition's. Back it that time, every railroad had their own rules, of which, most was not used on other roads. They liked their own rules. Frisco had a lot of Dimming rules.
     
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