\({E_B} - {E_A} = \frac{{hc}}{{{\lambda _2}}}\,\,\,\,\,\,\,\,......(2)\,\,\) અને
\({{\text{E}}_{\text{C}}}{\text{ - }}{{\text{E}}_{\text{A}}}{\text{ }} = \frac{{{\text{hc}}}}{{{\lambda _{\text{3}}}}}\,\,\,\,\,\,\,.....{\text{(3) }}\)
સમીકરણ \((1)\) અને \((2)\) નો સરવાળો કરતાં,
\(({E_C} - {E_B}) + ({E_B} - {E_A}) = \frac{{hc}}{{{\lambda _1}}} + \frac{{hc}}{{{\lambda _2}}}\)
\( \Rightarrow \,{E_C} - {E_A} = hc\left( {\frac{1}{{{\lambda _1}}} + \frac{1}{{{\lambda _2}}}} \right)\)
\( \Rightarrow \,\frac{{hc}}{{{\lambda _3}}} = hc\left( {\frac{{{\lambda _1} + {\lambda _2}}}{{{\lambda _1}{\lambda _2}}}} \right)\)
\( \Rightarrow \,{\lambda _3} = \frac{{{\lambda _1}{\lambda _2}}}{{{\lambda _1} + {\lambda _2}}}\)