I have always wondered just what makes a small light bulb a 3v bulb or a 14v or a 18v or a 24v bulb? They all look the same. Is it the size diameter of the filament or the filament type? Just curious.
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The diameter of the coils, the diameter of the tungsten filament itself, the length of the coil, etc determines how bright it will glow at a given voltage tungsten alloy with semi-conductive metals may allow the bulb to glow with low voltage, or simply a smaller length of filament coil with a smaller diameter.
A specific brightness standard is used to test different bulbs, the voltage current mix that provides the output most near the standard level will be marked for that bulb
the gas, whether its krypton, xenon or a mixture of halogens, are simply used as a filler gas within the bulb to prevent rapid oxidation of the filament. Krypton is the cheapest inert gas. It works, but over time you realize the bulb acquired a black haze within the bulb, that indicates tungsten atoms that has boiled off...which decreases the light output.
As far as I know, basically its going to be the gauge and length of the wire that makes up the filament.
Miniature bulbs are made with a variety of filament supports, and with the filament wire shaped or coiled in a number of different ways.
I don't know whether different metals are used.
The voltage of a bulb is determined by the resistance
of the filament only. The resistance cannot be measured
when the bulb is cold because a hot filament will have
maybe 10 times the resistance of a filament when cold.
If the bulb is rated for 3 volts and you put 8 volts on it
it will be very bright for a short time before burning out.
The resistance of the 3volt bulb will be less than that
of the 8volt bulb, maybe.
