Lyle,
There is an ICC/FRA regulation concerning the amount of illumination that a
headlight provides. It has to do with distance and lumens, something like a
certain amount of lumens at a certain distance from the front of the
locomotive, as I recall. There was something about illuminating a person
standing 400 ft. In front of the locomotive. I don’t know when that regulation
was established. The dual seal beam headlights provided more illumination than
a single incandescent bulb. EMD Engineers were always concerned with meeting
the regulation whenever designs were changed. They had reservations about
whether the primary headlight mounted on the short hood met the regulation, but
a number of RR specified that arrangement, including the Q. Other factors that
may have led to the change was the availability of the older bulbs as the seal
beam headlights became more common and reduction of their replacement parts
inventory. By the late 1950s, all the Q’s GP, SD, later E and switcher model
locomotives were delivered with seal beam headlights. I am sure that companies
like Pyle-National, recognized the situation as technology was changing and
developed a direct replacement kit for older locomotives with incandescent
headlights. Even some steam locomotives on other RRs were equipped with dual
seal beam headlights, and I think that the Mars lights on Q steam locomotives
may have used the same bulb.
Bill Barber
Gravois Mills, MO
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