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Photons are "light particles" which have a certain energy \( W_{\text p } \) (called **photon energy**). How large this energy is depends on the **frequency** \( f \) or the **wavelength** \( \lambda \) of the light used:`$$ W_{\text p } ~=~ h \, f ~=~ h \, \frac{c}{\lambda} $$`

Here \( h \) is the **Planck's constant** with the value: `$$ h ~=~ 6.626 \cdot 10^{-34} \, \mathrm{Js} $$`And \(c\) the **speed of light** with the value:`$$ c ~=~ 3 \cdot 10^8 \, \frac{\mathrm m}{\mathrm s} $$`