# [Physics] Why does light have multiple frequencies

The wavelength of visible light ranges from 750 – 400 nm, and so do the corresponding frequencies. However, a photon only has one frequency, given by $$E =h\nu$$, at a given time, and it can’t be changed unless the photon gets energy from somewhere, which isn’t possible in the vacuum; i.e. once it leaves the source it can’t possibly get enough packets of energy to become excited or even lose the energy to some other particle, as space is empty.
Light comes with so many wavelengths because it is made of so many photons. A typical lightbulb puts out something on the order of $$1\ \mathrm{W}$$ of power in the visible spectrum, while individual photons in the visible spectrum each have an energy on the order of $$10^{-19}\ \mathrm{J}$$. Therefore, a typical lightbulb will produce something on the order of $$10^{19}$$ photons per second. While each photon has one specific frequency, there are so many of them that the ensemble of photons appears to have a continuous range of frequencies.