How to calculate or measure the plane of angel for the light provided to a microalgae culture in photobioreactor?

In an experiment for the cultivation of microalgae a photobioreactor was designed with LED lights for the provision of light energy. The specifications of LED Lights are given as; wattage of 8 W, Beam angle 140◦, 560 lumen (Lm), power of current 69± 5 mA, color of light 6500K, frequency 50Hz.

Now the questions are;

1)      How 140 deg is numerically equivalent to 40 deg?

2)      What is meant by “planes” the angle is measured? And how it could be given least value?

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