According to the FRA:
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The FRA requires that the locomotive headlight (steady burn) used for road service have a luminous intensity of at least 200,000 candela. The headlight light focus angle in the horizontal plane in relation to the centerline of the locomotive must illuminate the track so that the locomotive engineer can identify moving or stationary objects or conditions at a distance of 244 m (800 ft) in front and ahead of the locomotive. The reduced luminous intensity (60,000 candela) and distance requirements (91.5 m [300 ft]) for railroad yard headlight operation is required to reduce excessive glare for railroad employees.
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At 200,000 candela the beam can probably reach 800 meters, although I'm not sure how well things will be illuminated. Just going by the inverse square law it would be about 1/3 lux at that distance, but the optics in the lamp can distort that rule.