The reflected light on the upper and lower surfaces of the film is coherent light. Because one of the reflected lights has a half-wave loss, the optical path difference =2ne+λ/2.

When the optical path difference is an integer multiple of the wavelength, the reflection is enhanced: 2ne+λ/2=kλ.

The wavelength of reflection enhancement λ=4ne/(2k- 1)

Let k =1:λ = 4ne = 4 * 5300 *1.33 = 4 * 6650+399 = 4 * 7049a infrared ray.

Let k=2:λ=4ne/3=4*7049/3=9399A infrared ray.

Let k=3:λ=4ne/5=4*7049/5=5639A visible light.

Let k=4:λ=4ne/7=4*7049/7=4028A Visible light let k = 5: λ = 4NE/5 = 4 * 7049/9 = 3133a Ultraviolet light.