There are two types of light sources that a photographer can make use of. Those that the photographer creates, and those that the photographer doesn’t create. Confusingly, though, even though there are only two types of light source, there are many actual possible sources, and the terms for them can often be confused with each other. For instance, available light is light that is already present in the scene. It’s not created by the photographer.
Many think of it as being natural light – i.e light created by nature. Typically natural light is from the sun and it may be as direct as the sun in a clear blue sky, or as subtle as the sun behind a blanket of cloud on an overcast day. It may be daylight coming in through a window, or the light at the end of a tunnel. But available light may also be artificial light: a lightbulb in the ceiling, the chandelier over a dance floor, the coloured disco lights of a band. They are all artificial light sources, but are also available light for the photographer.
Flash is also an artificial light source, but that’s not already in the scene – that needs to be initiated by the photographer, as distinct from those other artificial sources of light we’ve listed that the photographer doesn’t create.
If we want to talk about light in a photo – especially for the purposes of understanding it and learning it – we really only need to divide that light into what the photographer creates and what the photographer doesn’t create. Thus we need terms that factor in all of the above with no confusion. Rather than use the term available light for light the photographer doesn’t create, I prefer to use the term ambient light. Here’s how I will define it.
Ambient light – light that the photographer doesn’t create, but which is present and impacting the scene they are photographing.
For light that the photographer does creates, rather that call it artifical light or even flash light, I will use the term added light. Most of the time it will be artificial light but it could be natural light (e.g. a reflector placed on the shadow side of someone’s face). And generally for me the source of that added light is a hotshoe flash (i.e. a flash that can be mounted in the hotshoe of your camera, although it’s often used off the camera also), but it may be a studio light (sometimes called a big light) or a continuous light source such as a video light.
So regardless of the type of light, where it is deployed specifically for the purposes of creating a photograph, I will call that added light:
Added light – light that the photographer creates and adds to the scene they are photographing it in a way that is entirely under their control.
The reason we want to divide light into two sources is that it helps us to be able to think about how we expose for each aspect separately.
More often than not the secret to making a well lit photo is to think about the ambient light and the added light separately, and to balance how they interact. Many times where an image uses added light, it also makes use of the ambient light, especially in a wedding situation.
That’s true of the first dance photo at the top of this post, for instance – the bride and groom are lit by a combination of flash (added) and the room lights (ambient), which are there whether or not I take my picture. The room itself is lit by artificial wall and ceiling lights and candle light. What’s important is that all of those elements balance well with each other.