Natwerk Designs

How could you design a light bulb that could be used in a series circuit so that if the filament burnt out...?

Sorry the question cut off the the end to it should read: so that if the filament burned out all the other lights would continue to glow. Feel free to include diagrams:)

Public Comments

1. put it in a parralel circuit :p
2. The same way they do Christmas Lights, they build in a parallel resistance into the bulb that higher than the filament so that when the filament was intact, most of the current flowed through the filament but when it burnt out (opened up) the current would flow through the resistor, by passing the open filament
3. A parallel circuit really is the way to go for this problem. The problem with putting a high value resistor in parallel with the filiament is when the filament burns out, current must flow through the higher value resistor which causes a voltage drop that is larger than that across any of the working lights since its resistance is higher, this decreases the voltage drop across each light and may dim them too much to be good. One way may be to use enough diodes in series, in parallel with the light, such that their combined turn on voltage is just slightly higher than that of when the light is on. Then, with the light on all the current flows through the light because the voltage drop is just below that needed to turn on all the diodes to let current flow through them. Then if the light blows the drop will increase across the diodes until they turn on and allow current to flow dropping only slightly more voltage than the light itself did when lit, hence the other lights would have nearly the same voltage across them as they did before the light blew out and would remain nearly as bright. If its an AC voltage applied to the circuit just use the same number of diodes in the opposite direction. Again the turn on volatge should be just above that used when the light is on, soo when it burns out they will turn on regardless of the signal direction.
4. Actually the technique used in Chrismas lights is the way to go. A piece of wire with a thin oxide layer is wrapped around the two wires that feed the filament. If the filament burns out, the high voltage breaks down the oxide layer creating a short circuit, so the other bulbs continue to glow. During normal operation, the 2 volts or so is not sufficient to break down the oxide layer. It is similar to the Ovshinsky effect, kind of a low tech version.