I don't know, what primary energy source does the lighting system use (to charge the batteries,...), if the generators driven by the car movement or a cable from the locomotive. If it is only the car movement, there have to be quite complex battery charge management system in order to prioritize the loads based on the charge state (allow the use of the battery power by all fancy things like high output lights and power outlets, while still ensuring there is always enough juice left for the safety equipment, like tail lights or so...).
And this need the lighting to have multiple dimming levels (full output when the primary power source is available, reduced output when it disappear for longer time and minimum output when the battery charge state becomes too low). And for that the most efficient way is to use three separate lamps with apropriate output levels and power needs.
And the manual light switches there allow the manual changeover to the lower setting.
And indeed, the T12 are still used, because the T8 are compatible with T12 only on the preheat ballasts, nowhere else.
