E(r,θ)=E0(r)cosnθ
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Here, ϴ is LED light-emitting angle, E0(r) represents the illuminance distribution of the surface light source when ϴ = 0°. Since the luminous intensity distribution of a standard Lambertian surface light source is approximately an ideal cosine function distribution, so the value of n for a standard Lambertian surface light source is approximately 1.
Through the above analysis we know that:
(1)
when ϴ = 0°, the luminous intensity is maximum;
(2)
when ϴ = 90°, the luminous intensity value is approximately zero. However, in the practical application, the value of n for the LED often increases due to same reasons (e.g. encapsulated reasons) with the increase of the light-emitting angle. So it is usually greater than 1.
(3)
when 0° < ϴ < 90°, if View the MathML source, View the MathML source