Coming home this evening from Asheville I happened to look to the right off a bridge on the interstate and saw a NS train. As we all know, the headlamps on locomotives are very bright and project far down the track, but when seeing it I wondered what kind of headlamps they are. Xenon or another noble gas came to mind at first because of the brightness, but those are expensive and the lights don’t have that “blue glow” to them like with xenon. I suppose they are regular halogen lamps by the way they look, but just wondering what they actually are.
…And they can dim them too. They had very bright lights before Haglogen assemblies were around years ago…But it’s possible a change has been made in later years.
Ed and Randy can chime in with specific information.
Some stuff taken from another site that might be relevant here:
The resistor values of the control to a locomotive headlight are:
Supply voltage = 74 volts
Bulbs: PAR-56 30 volts/200 watts (see relevant FRA spec, 49 CFR 225.125)
Primary resistor = 4.7 ohms
Bright = 1.6 ohms
Medium = 1.3 ohms
Dim = 5.6 ohms
Resistors are cumulative
ie Bright = 4.7 + 1.6
ie Medium = 4.7 + 1.6 + 1.3
ie Dim = 4.7 + 1.6 + 1.3 + 5.6
I dug this up on one of my schematics.
According to the GE electrical schematics for the Southern Pacific B30-7’s, the headlight voltages are as follows:
Bright = 30V
Medium = 22V
Dim = 14V
Bill Kaufman
The specs were run through a computer program also:
Assuming a bulb resistance of 3.5 ohms …
Bright = Bulb voltage drop 26.43 V, Power 200 watts
Medium = Bulb voltage drop 23.33 V, Power about 156 watts
Dim = Bulb voltage drop 15.5 V, Power about 68.8 watts
Harold Scadden
Many in the field of electronics are appalled on being informed of the circuitry involved in supplying voltage to the headlights and oscillating lights. As discussed above, however, this was necessary because of the mechanical stability of the filaments in the bulbs used. The idea of high wattage resistors and their associated “wasted heat” is in conflict with the new efficient methods of voltage conversion. The problem seems to have been that the bulb manufacturers could not readily come up with a strong enough filament at a standard locomotive voltage [to] end the inefficiency of the electrical lighting systems. This has improved, however, wit
Conrail used 75 volt bulbs. This causes problems on CSX when the wrong bulb is used. You either get a dim light or a very bright light for a very short time.
good reserch guys
…Years ago I had a set of lights in my '62 super sport Chevy and that was long before halogen…They projected a narrow beam down the highway…{high lights, with 4-light system}, and really lit far down the road. Believe they were a part number used by some aircraft landing lights. Didn’t use them long as I suppose they were not legal for sure…and I still have them sitting in boxes…When we’re younger we are more willing to try such stuff…Now we have excellent lights right from the automotive factory. With ditch lights on locomotives now I suppose their lighting ability helps the crew see better too…Especially see better at night just where they are.
Good grief. Overmod really went into the encyclopaedia! Thanks!
Only thing I might add is that the brightness of the headlight is also used to indicate that a train (or engine) is in the clear – if you see a headlight on bright, you have to assume that it’s on an engine which is NOT in the clear for you, and you may have a problem! So… if the headlight goes out, not only do you have problems at crossings, but you have some very interesting flagging considerations…