How to check voltage and wattage of an unmarked incandescent bulb?
An incandescent bulb is like a resistor, so the more voltage that is applied the more current is sinked and therefore power that is beign dissipated. There will be a maximum power that it can withstand before braking. If you want to find this out, connect one bulb to a power supply and measure voltage and current. Start off at 0V and increase the voltage slowly until the bulb start lighting. Then you can keep on going until the bulb explodes. There you found it maximum limit. I would recommend not applying more than 70% of that voltage continuosly to the rest of the bulbs.