Good light is subjective, as is it’s appreciation.

For me I like certain types of light for certain types of subjects. Take sunlight for example. Generally my rule of thumb with sunlight is that the closer it is to the horizon the better the quality of light, especially in regard to portraits or landscapes.

If I was to shoot a portrait of a person in the middle of summer in the sunshine at midday day, that in my opinion would be poor light for the subject. The high angle of the light would cast shadows under the nose and the chin and the cheeks and the eye sockets. Terrible light.

On the other hand if they were standing under a tree the light would be so much softer on their face and would reveal their features in a much more flattering way. Better still, if I were to photograph them at sundown where the light is horizontal or just after sundown where the light is particularly soft that would be nice flattering light in my opinion.

Light can be soft and cast graduated shadows on the subject or it can be hard and cast very sharp shadows. Soft light comes from a broad light source, like an overcast sky or light filtering in to a room through a window. Haed light is cast from a small light source, by direct Sun or a spotlight or direct flash.

So a broad light source is soft, a point light source is hard. That is the quality of the light. Not to be confused with the quantity of light.

To get a feel for it try this: Create hard (point source) or soft (broard source) light and use it to illuminate a subject to see the result. Light stuff from the top or the front or the sides. See what it does. If you can’t create the light find it and do the same thing.

I hope this is helpful. I could add so much more. If you have any questions or need clarity feel free to ask.