How to wire 12V bulbs on a 36V circuit?
3 12v lamps in series will work 3 x 12 = 36. 
There can be additional sets in parallel if your supply is large enough. The wattage for each set of 3 will be the wattage of 1 lamp. Example a 20 watt 12v set of 3 will draw 20 watts at 36v. A second set of 3 in series with each other would draw a total of 40w and a 3rd set the total would be 60w. If 1 of the lamps in a 3 bulb set burns out the other 2 will go out until the bad lamp is replaced in that series circuit. Additional parallel sets would not be affected.