We have all had to deal with specular highlights, even if we did not know what they were called.

Think about portraits of people you have made in direct sunlight. Remember that glaring spot on their face or forehead? That was the specular highlight of the sun. And if the person was sweating or had oily skin it only made matters worse, as that sheen is very efficient at throwing back a hard specular.

That reflection is a function of the intensity of the light source. More specifically, think of it as intensity per square inch. And understanding this starts to tell us how to control it.Read more »

http://strobist.blogspot.com/2016/07/lighting-102-controlling-specular.html