Question

how can we know the intensity of light

Answer 1

Heya user
Here is your answer !!

The intensity of light can be measured through a physical quantity called luminous intensity .
Its S.I. unit is candella .

Hope it helps !!

Answer 2

1.  Understand photometers that measure lux and foot-candles. These are units that describe the intensity of light on a surface, or illuminance. ...
2.   Know how to interpret illuminance units. ...
3.  Understand lumens and luminance. ...
4.Measure beam and field angle.