What size resistor for a simple circuit do I need?

I have a 12vdc power supply powering a 12vdc bulb and I would like to maximize the bulbs life by adding a resistor yet still keep it bright enough to visibly see. I purchased a 270 ohm, 1/2 watt, 5% tolerance package of 5 resistors just in the hopes of getting close to right but I don't really know for sure... show more I have a 12vdc power supply powering a 12vdc bulb and I would like to maximize the bulbs life by adding a resistor yet still keep it bright enough to visibly see. I purchased a 270 ohm, 1/2 watt, 5% tolerance package of 5 resistors just in the hopes of getting close to right but I don't really know for sure anything about resistors. Can you help? The resistors are returnable if they are the wrong size.
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