High Key Lighting-
High-key lighting simply refers to images that are mostly bright, with a range of light tones and whites and not very many blacks or mid-tones. In high-key photography, tones that generally would have been mid-range become much brighter, near-white tones become white and white becomes white.
A basic studio lighting set up for high-key photography consists of a key light and a fill light, with your key light two times the brightness of the fill. The background should be lit independently–preferably with two lights positioned three to five feet away at 45-degree angles. These background lights should be at least one stop brighter than your subject lighting. This will result in the blown-out background that you’re looking for in a high-key image.
High-key images can also be obtained in the studio with a pastel-colored background, though white is more common and generally simpler to work with. As for your model, you can certainly achieve a high-key effect regardless of what she’s wearing, but you may find yourself more satisfied with your work if she’s dressed in lighter colors or in white. http://www.digital-photo-secrets.com/tip/3558/using-lighting-style-to-create-mood-high-key-and-low-key-lighting/#sthash.ahp6OQmp.dpuf



Low Key Lighting-
low-key lighting relies on shadows, deep blacks and darker tones, with very few whites and middle tones. The mood is opposite, too – while high-key lighting is hopeful and optimistic, low-key lighting is somber, mysterious and moody, dramatic or even ominous depending on the subject.
A low-key studio set up is a lot simpler than a high key one. You just need a single light source and a dark or black backdrop. You may find having a reflector on hand can be helpful, too, though in many cases all you will need is that single light source. As a general rule, keep the light off of your back drop and on your subject, but other than that you have a lot of freedom as far as where you choose to place your light source
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