How do you measure the brightness of the light?

Question

We can see that under the sun it is very bright and under the shade is bright but it is still brighter under the sun. we can see the difference by the naked eye. How do we calculate it or measure it and give a a numerical equivalent?

Answer 1

I think its a unit called LUX, 1 lux being the equivalent of the light from one candle and the other end being full noon sunlight

Answer 2

Candela.