The Mars light on Q locomotives, was a warning light. Below that light on those locomotives was a two bulb road headlight. As a warning light, the primary use was the the white oscillating light that was intended to warn the public and RR personal of the approaching locomotive. If memory serves, the red light, also oscillating, was normally only activated when an emergency brake application was made on the locomotive. This warned other RR personal that the train was in an emergency situation. It basically had no purpose as far as the public was concerned. Apparently, the Operating and Mechanical Dept. decided that because of it's much more frequent use, the white light should have the more prominent position. It was certainly a matter of preference and that was theirs at the time. Q steam locomotives that were equipped with Mars lights, were arranged in the same manner.
Keep in mind that, while most automotive traffic signals have the red on top that is not necessarily true in the RR industry. Where three position signals are used (common on many RRs), the green is on top and the red is on the bottom.
Fri Jan 4, 2013 1:23 pm (PST) . Posted by:
High on the ends of the early hood units just above the yellow over red stripe was a light housing unit which I have always understood to be a Mars light. It had 2 lamps and the lenses were clear over red. Intuitively one would reasonably assume that the red, being generally a more restrictive and urgent communication, would be in the more prominent "high" position, but pictures show otherwise. Why is this so?
I have just had a professional modeler, customize and overhaul an Atlas GP7, and while he ( not a devoted CB&Q fan) was supplied with many color photographs of the prototype, and was clearly instructed to place the clear lens above the red lens, he did otherwise. To be sure, to my eye, that arrangement is more aesthetically pleasing... so I am not inclned to change it [ I have already spent over a year and a half on this project and it must end ] ….. But it is not correct. Will welcome any comments about why the red lens is below the clear lens on the prototype.