What makes a lightbulb glow? I am self-studying electricity and magnetism, and I am confused about a point.
I have learnt that the drift speed of an electron is extremely small. However, according to Drude's model, the electron jumps around very fast and bounces against other particles in a conductor.
I also read that this random movement happens even in the absence of electric field.
But how this is possible? Electrons should lose kinetic energy when bouncing off particles, and should become slower and slower. Maybe this process takes really long time and thus we can consider the slow down negligible?
But then what is making a lightbulb glow? I know it is heat generated by bouncing off particles. In my naive understanding, I thought this was dependent on the flow of electrons, but I am now doubting this since they are drifting really slowly.
Is it the random scatter movement? That's also weird: if the electrons are scattered around even without a field, then the lightbulb should glow even without a voltage source, which doesn't happen.
So my questions:

*

*Does the "scattering speed" of the electrons depends on the presence of an electric field?


*What makes the lightbulb glow? Is it the electron slowly drifting? Is it the scatter speed increasing due to the electric field? Both?
What is really going on then?
 A: When electrons bounce of off other electrons and/or molecules, they lose kinetic energy. At the same time the other party in the collision will absorb energy. Energy must always be conserved, so it is never "zero action" in an element which is not at $0K$. The drift of carriers in a material is proportional to the temperature.
An applied electric field (voltage) will put free electrons in the unidirectional motion required for a net current to form. These travelling electrons will then, as you say, impact with others with them giving and taking energy from one another. If the electron collides with something other than another free electron, the material structure itself absorbs this energy. In this case it is no longer translational energy but rather vibrational and/or rotational. This heats up the resistor and the resulting radiation (light) is best modelled with a blackbody-model where the spectrum and intensity is determined by the temperature of the filament.
When there is no applied voltage, there will be random movement of charges as you say. However, this is on a smaller, local scale. On the larger scale of the filament, there is no flow of electrons other than the random movement of electrons. A current is typically defined by the unidirection movement of electrons in one or several directions.
A: Assuming you are discussing an incandescent light bulb, the glow literally is a result of blackbody radiaton as the (usually) tungsten filament will heat to temperatures of ~3000K. The light bulb is acting as essentially a resistor, where the filament is slowing down the flow of electrons, emitting heat and light. But tungsten itself is not a normal resistor in that it does not follow Ohm's law, and you'll find that as the tungsten heats up, its resistance increases. Thus light bulbs are 'non-Ohmic resistors'.
In terms of your question regarding the relationship of electron drift velocity, this article may help: "the speed of electricity"
