Will connecting a 12V 21W filament bulb to a 12.5V battery source burn it ?
The supply is a 12V 7AH sealed lead acid battery. After connecting the bulb directly to the battery which currently is at 12.5V, I see a black mark on the bulb glass mount. Does this mean that the supply is too high and it is going to burn out ?
No that will be OK>
If you put a volt meter on your car battery it can be 14 volts and all your bulbs are 12 volts but they do not blow.
The black mark was put there in manufacturing.
It is called gettering.
When a bulb is made the gettre is turned on in the bulb and it blows consuming the oxygen in the bulb so that the filament does not blow.
This sometimes leaves a deposit you can see, but usually the deposit falls into the cap of the bulb.
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