For many LED optic projects, a spot size and beam angle can be specified with a single uniformity value. In cases of beam angles above 30 degrees, things get tricky. Please see the images below for an explanation.
If you prefer to understand the math…
Illuminance is changed by formula E=(I/r*r)*cos(A), where E – illuminance, I – luminous intensity, r – distance to spot, A – angle of ray.
Distance r is usually constant. If the dependence of I from A is constant, we have illuminance falloff at high A values because cos (A) multiplier is smaller.
With beam angles above 30 degrees, it is tricky to specify with a single uniformity value the spot size and beam angle
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