# How do light bulbs really work

• p.tryon
In summary, black body radiation is emitted when an object gets hot. The radiation is determined by the temperature of the object and the amount of kinetic energy the object has.

#### p.tryon

I understand that the filament is heated by resistance and glows indandescently. What is the actual mechanism for the emission of light by incandescence? Are the electrons actually excited to higher energy levels or is something else going on?

If the electrons were excited to higher energy levels (and then de-excited to emit photons) the light would only be at discrete wavelengths (e.g. in a sodium vapour lamp or a compact fluorescent lamp), and not continuous across multiple wavelengths as it is.

To add to that, you might think the filament getting to ~3-5,000K is ridiculous, but that is the case. Light bulbs are under vacuum however, that is why it doesn't blow up or anything :)

Thank you for your replies. That is interesting about the vacuum thanks. What is the actual mechanism of black body emission?

p.tryon said:
Thank you for your replies. That is interesting about the vacuum thanks. What is the actual mechanism of black body emission?

It's a great question and when it was first considered it kick started quantum theory. May I suggest that you start by googling the black body radiation curves.

My understanding, from Einstein's theory using his A and B coefficients, is that heat in a blackbody radiator is manifested in the kinetic energy of the particles, not in excited orbitals. The temperature of a medium is related to the average kinetic energy of the medium's atoms or particles. A photon carries with it a discrete amount of energy/momentum. When a photon strikes an atom, the atom absorbs the momentum and experiences an imparted impulse which moves the atom. These imparted impulses give rise to the kinetic energies that create the heat. So if we have a mass of oscillating/moving atoms, our blackbody radiator at a given temperature T, then they will spontaneously, and under stimulation, radiate some of their kinetic energies as photons. The probabilities at which these radiations occur (both stimulated and spontaneous) give rise to the Planck distribution. When photons are radiated from an atom, then the reverse happens from absorption, the atom loses a discrete amount of energy/momentum equal to the energy of the emitted photon.

EDIT: Should make it clear in light of Division's post that Einstein's derivation was done before Quantum Mechanics described the atomic orbitals. Einstein related the kinetic energy gain from absorption to being countered by a retarding force. This last part here is not necessary to derive the Planck spectrum. So whether the energy that is being emitted is stored in excited orbitals or a kinetic energy of the atom is immaterial, the main assumption was that the energy emitted had to be done in discrete energy levels and the emissions could occur spontaneously or via stimulation.

EDIT EDIT: Wait.. where did Division's post go... Ninjas! \shiftyeyes

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## 1. How does a light bulb produce light?

Inside a light bulb, there is a filament made of tungsten that is heated up by an electric current. This causes the filament to emit light, known as incandescence. The light produced is a result of the filament's high temperature.

## 2. Why do some light bulbs give off different colors of light?

The color of light produced by a light bulb depends on the material used for the filament and the temperature at which it is heated. Tungsten filaments emit a yellowish light, while other materials such as mercury or halogen can produce different colors when heated.

## 3. How does a light bulb convert electricity into light?

A light bulb has a thin wire inside called a filament, which is made of a material with a high melting point, such as tungsten. When electricity is applied, the filament heats up and emits light. This process is known as incandescence and is the main way that light bulbs convert electricity into light.

## 4. Why do some light bulbs last longer than others?

The lifespan of a light bulb depends on the type of bulb and the material used for the filament. Incandescent bulbs have a shorter lifespan because the filament gradually burns out over time. LED bulbs, on the other hand, use much less energy and have a longer lifespan because they do not use a heated filament to produce light.

## 5. How does a light bulb turn on and off?

A light bulb turns on when an electric current is passed through the filament, causing it to heat up and produce light. It turns off when the current is cut off or interrupted, causing the filament to cool down and stop emitting light. This can be controlled through a switch or a circuit in the lighting system.