One Light?: The truth is that there is usually more than one light because where there is light there usually is reflected light.
You can use this reflected light if it helps or insert gobo’s (black go between boards or flags) to stop this. You can increase the reflected light by using reflectors, expensive ones or shirts and white boards.
Hard and Soft: Simply the difference between the light on a sunny day and a cloudy day. Hard light gives dark well-defined shadows. Soft light comes from many different places.
Bright and Dim: A dim light to us can be made to look like daylight, simply by leaving the shutter open for longer. So in this respect there is no such thing as bright or dim light. That is defined by the camera settings. The camera can make the brightest of scenes look like it was taken during an eclipse!
Small and Big: The sun is the biggest light that we can use, however it is called a small light because it is so far away. But put the clouds in between us and the sun and it becomes the biggest light we can use.
Soft boxes turn small lights into big lights and are often 2-3ft across. Alternatives are to shoot through a white sheet or bounce off a wall. An umbrella can achieve a similar effect because it spreads the light all over the place and reflected light can soften the shadows.
White and White: To the human eye, white is clearly white; that is because the eyes is constantly adjusting and interpreting what it sees. Cameras are not able to do that to the same extent. Collect different sheets of white paper and take a close look at them - you will probably find quite a range of whites. The same variations apply to light. We would call them all white (non coloured) but in reality they are coloured or tinted in some small way.
Different lights produce different tints - fluorescent give a greenish light, incandescent give a orange tint, flash guns and strobes will tend not to have a tint; so whites look white to our eyes but some appear coloured to a camera.
White and Coloured: Taking a photograph indoors with flash and incandescent bulbs will give a mixture of white and orange tints.
I was taking an outdoor photo during the day with a deeply overcast day. I place two flashguns with orange gels and the photograph turned from a dull picture to one that looked as though it had been taken late in the evening with a lovely warm glow.
Placing coloured gels over a flashgun colours the light and will produce different effects. Quality street sweets are famous for providing different colour wrappers that can be used for different effects.
Direct and Reflected: Direct light comes from your source light and usually has an obvious effect. Reflected light will come from any other surface that is not totally black. A coloured wall will give the light a colour tint. A shiny surface will give a hard strong light. A textured surface will give a soft weak light.
The distance from the source to the reflecting surface and then to the subject, compared to the distance from the source light to the subject, will greatly affect the strength of the reflected light.
Fast and Slow: What I am really referring to is the duration of the light, ie how long the light is shining while the photograph is being taken.
Daylight shines 100% of the time the shutter is open and a flashgun can shine for 1% of the time. In most cases though, you will get a combination of two lights; one shining 100% and the other a fraction of the time.
Front, Side and Rear: Choose the position of the main light. Each position will create a very different effect, from fully lit to silhouette. Reflected light can be used to fill in shadows.
Low and High Key: This is were the tones of the photograph are primarily dark or bright. The details of the subject are either blown out or in deepest shadow. Often the form comes from the outline of the subject. This is achieved by under or over exposing the subject.
Invisible: Infra Red is not visible to the naked eye, but filters can be attached to a camera which allows that light to be picked up on the sensor or film. This can produce a surreal effect. Different surfaces reflect different amounts of infra-red.
So there we have it, a lightening, fast pass over variations with just one light. An unabridged version of this article and others can be found at John's Photo Blog on his website.
All this with just one light; just think of the variations with two or more lights.
Explore my website to see some of these effects in practice in the Galleries. Explore making your own photographs with just one light. Explore, discover and understand.