These 10 animal facts will amaze you. Solar glass is a type of window and building material that is designed to block radiant heat transfer, which is basically the amount of heat from the sun that passes through the glass and into whatever space is on the other side.
Human skin color can vary from almost translucent to almost black. This range of colors comes from the amount and type of a pigment called melanin found in the skin. There are two types of melanin--eumelanin and pheomelanin. In general, the more eumelanin in your skin, the darker your skin will be. People who make more pheomelanin than eumelanin tend to have lighter skin with freckles. Like many other traits, the amount and kind of pigment in your skin is controlled by genes.
What causes elbows, knees and certain areas of body skin to darken? One of the most common causes of darkened skin in these areas is contact or photocontact dermatitis. Contact dermatitis occurs when the skin is irritated by its contact with irritants or allergens. Photocontact dermatitis occurs when those irritants are stimulated by light (many allergens, such as fragrances, dyes and preservatives, are also photo-allergens, which can react with light to cause darkening).