Interesting question.
There are a number of factors that may attribute to the pricing of an item say quality of material, number of special features available, and certainly a common notion of brand value (e.g H&M vs GUCCI). Of course, it does not necessarily mean more face value = more expensive.
Typically, to estimate, I would check the brand and material component.
The sun is the primary source of light. Other artificial sources are light bulb, torch light and some others. Thats all i can think of.
