# How is white light made up of all the colours in visible light?

## Main Question or Discussion Point

In a light bulb, is the filament made up of elements which each produce a colour of visible light to make white?

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White light is seen by the human eye because all frequencies (each color) are being produced. More formally, the power spectral density is uniform over the visible light spectrum. This means that each of the eye's cones are stimulated equally. Therefor the filament of a light bulb is emitting energies uniformly across the visible light energy spectrum. Each wavelength (which defines color) is given by lamda=c/v, where c is the speed of light and v is the frequency. This frequency is directly related to the energy of the light wave by Planck's constant, h (E=hv). Thus, each characteristic energy (in the visible light spectrum) is being emitted by the element. In the case of conventional filaments, this element is Tungsten. Due to the high melting point of tungsten, the variety of photon emissions is large enough to cover the visible light spectrum (since they are dependent on temperature).

Hope this helps!

White light is seen by the human eye because all frequencies (each color) are being produced. More formally, the power spectral density is uniform over the visible light spectrum. This means that each of the eye's cones are stimulated equally. Therefor the filament of a light bulb is emitting energies uniformly across the visible light energy spectrum. Each wavelength (which defines color) is given by lamda=c/v, where c is the speed of light and v is the frequency. This frequency is directly related to the energy of the light wave by Planck's constant, h (E=hv). Thus, each characteristic energy (in the visible light spectrum) is being emitted by the element. In the case of conventional filaments, this element is Tungsten. Due to the high melting point of tungsten, the variety of photon emissions is large enough to cover the visible light spectrum (since they are dependent on temperature).

Hope this helps!
Ok, but how can one element emit different frequency photons? I thought that each element only emitted one frequency of photon?

Ok, but how can one element emit different frequency photons? I thought that each element only emitted one frequency of photon?
Each element has a number of energy states that it may undertake. This energy state is based on how excited the atom is, largely governed by its temperature (i.e. something really hot has more energy than something very cold). All atoms strive to restore their ground state, for this reason a variety of photons may be emitted. As the atoms are closer to their ground state, the energy of each photon (which parallels to its color) will decrease. Given the proper voltage, tungsten reacts ideally to produce the entire spectrum of photons.

your thinking of like the spectral lines of an element and the discrete orbitals. But when you have a slab of iron, having all theses iron atoms next to each other changes the overall collective behavior of the material . Like when i heat the iron with a torch it will eventually glow red and then i could eventually heat it hot enough to emit white light.

russ_watters
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