Formula: Photon Energy Wavelength
$$W_{\text p} ~=~ h \, \frac{c}{\class{violet}{\lambda}}$$
$$W_{\text p} ~=~ h \, \frac{c}{\class{violet}{\lambda}}$$
$$\class{violet}{\lambda} ~=~ h \, \frac{c}{ W_{\text p} }$$
$$h ~=~ \frac{ \class{violet}{\lambda} \, W_{\text p} }{ c }$$
$$c ~=~ \frac{ \class{violet}{\lambda} \, W_{\text p} }{ h }$$
Photon energy
$$ W_{\text p} $$ Unit $$ \mathrm{J} = \mathrm{Nm} = \frac{ \mathrm{kg} \, \mathrm{m^2} }{ \mathrm{s}^2 } $$
Photon energy is the energy of a single photon (light particle). You can calculate it using the wavelength of light \( \lambda \). For example, if the light has the wavelength \( \lambda = 550 \, \mathrm{nm} \), then the energy of a photon is:
\begin{align}
W_{\text p} &= 6.6 \cdot 10^{-34} \, \mathrm{Js} ~\cdot~ \frac{ 3 \cdot 10^{8} \, \frac{\mathrm m}{\mathrm s} }{ 550 \cdot 10^{-9} \, \mathrm{m} } \\\\
&= 3.6 \cdot 10^{-19} \, \mathrm{J}
\end{align}
Wavelength
$$ \lambda $$ Unit $$ \mathrm{m} $$
Wavelength of the electromagnetic radiation. Radio waves, for example, have a long wavelength. X-rays, for example, have a short wavelength.
Planck's Constant
$$ h $$ Unit $$ \mathrm{Js} = \frac{ \mathrm{kg} \, \mathrm{m}^2 }{ \mathrm{s} } $$
Planck's constant is a physical constant from quantum mechanics and has the value:
$$ h ~=~ 6.626 \, 070 \, 15 \,\cdot\, 10^{-34} \, \mathrm{Js} $$
Speed of light
$$ c $$ Unit $$ \frac{\mathrm m}{\mathrm s} $$
Speed of light (in vacuum) is a physical constant and has the value:
$$ c ~=~ 3 \cdot 10^8 \, \frac{\mathrm m}{\mathrm s} $$