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Example: Calculate the photon energy of a He‑Ne laser that emits light at a wavelength of 632.8 nm. Step 1: Write the formula for photon energy: E = h·c / λ, where h = 6.626×10⁻³⁴ J·s (Planck's constant), c = 3.00×10⁸ m/s (speed of light), λ = wavelength. Step 2: Convert the wavelength to meters: 632.8 nm = 632.8 × 10⁻⁹ m = 6.328×10⁻⁷ m. Step 3: Plug the numbers into the formula: E = (6.626×10⁻³⁴ J·s × 3.00×10⁸ m/s) / 6.328×10⁻⁷ m. Step 4: Multiply the numerator: 6.626×10⁻³⁴ × 3.00×10⁸ = 1.9878×10⁻²⁵ J·m. Step 5: Divide by the wavelength: E = 1.9878×10⁻²⁵ J·m / 6.328×10⁻⁷ m = 3.14×10⁻¹⁹ J. Step 6: If you want the energy in electron‑volts (1 eV = 1.602×10⁻¹⁹ J), divide by that factor: E = 3.14×10⁻¹⁹ J / 1.602×10⁻¹⁹ J/eV ≈ 1.96 eV. Result: Each photon from a He‑Ne laser carries about 3.14×10⁻¹⁹ joules, or roughly 1.96 electron‑volts of energy.