# When a bulb is rated at 12V does it mean the voltage drop across it or the voltage of the battery it is connected to?

If we had two light bulbs rated at 6W at 12V both in a circuit where the battery supplies 12V and they were connected in series, doesn't this mean that there would only be a 6V drop across each light bulb?

Does this mean that these lightbulbs aren't in their ideal functioning environment of 12V? Or does the rating simply mean the battery voltage which the circuit is connected in which case these lightbulbs are in their ideal functioning environment?

This problem is bothering me because depending on which I consider I find different answers for the current that flows through the circuit. I would really appreciate some clarification.

• 6W at 12V means that the bulbs are designed to be operated at 12V and will put out 6W when so operated. As you pointed out, they will not be operating at 12V in your circuit but at 6V. They'll glow much more dimly than their normal brightness (if they glow at all) in the circuit shown.
– user93237
Aug 10, 2019 at 1:37
• Also, at lower voltages, in addition to being dimmer, the resistance of the bulbs will also be lower, so they will draw more current at 6 V than half the current they draw at 12 V.
– Puk
Aug 10, 2019 at 1:40
• @Puk this is considering a real-life situation right? But if we were to consider theoretical - would I be correct in considering 1 bulb first and finding the current, then halving it for two bulbs? Aug 10, 2019 at 1:44
• I'm not sure what you mean by theoretical. If you mean the light bulb always has the same resistance regardless of the voltage applied (or in other words is "perfectly Ohmic"), then yes. This is just far from the truth in a real light bulb. At higher voltages, the filament of the light bulb will reach a higher temperature, increasing its resistance.
– Puk
Aug 10, 2019 at 1:49