1. Ambient light only.
2. Overpower ambient, use artificial light.
3. Mitigate ambient light, e.g. fill flash.
4. Enhancing ambient light or simulating ambient light.
Self-explanatory. A good strategy when the ambient light already has or can be modified to have favorable quality, direction, color, and intensity.
- Pros: lighting looks natural.
- Cons: May be difficult to get favorable quality, direction, color, and intensity.
- General technique: modify the ambient as necessary, meter for the ambient as key.
Artificial light becomes the key light, and ambient becomes the fill or is minimized. Fine strategy when there’s not enough ambient, or the ambient is unfavorable. Ideal strategy if we want a literally “unreal” look.
- Pros: allows significant control over the lighting.
- Cons: can look unnatural; the lighting might call undue attention to itself.
- General technique: underexpose ambient by 1 or 2 stops (or more), use a high shutter speed (if you want to minimize the ratio of ambient to flash, use sync speed), expose for flash as key.
- Examples: check out the photos from the flickr Strobist group that look surreal.
Ambient light sometimes has unfavorable aspects, but instead of overpowering it, we mitigate the ambient’s unfavorable aspects. For example: midday sun causes harsh shadows on faces and contrast is too high. One way to mitigate such light is to fill in the shadows with a reflector or a flash.
- Pros: lighting looks natural.
- Cons: must give up some control of the light.
- General technique: meter for ambient as key, underexpose flash by 1 or 2 stops.
- Examples: check out Neil van Niekerk's excellent tutorial on flash techniques, particularly those where he talks about lifting shadows.
Sometimes, the ambient light or the source of the ambient light has a significant role in the photo, but is unusable in its existing state. Artificial light is modified so that the light appears to come from the source of the ambient light. For example, a portrait lit by a single candle. In this approach, instead of just using a softbox to light the subject ‘properly,’ the color, direction, and if practical, the quality of the artificial light are modified to match those of the candle (e.g. a flash with a flame gel, reflected against a not-too-soft reflective umbrella positioned to give light from a similar direction from the candle).
- Pros: lighting looks natural, allows significant control over the lighting.
- Cons: requires more analysis and planning/preparation.
- General technique: analyze the ambient light’s color, direction, and quality. Modify the flash to have similar (not necessarily identical) color, direction and quality. If ambient has sufficient intensity, meter for ambient as key, underexpose flash by 1 or 2 stops. Otherwise, meter for flash, allow as much ambient as practical.
- Examples: check out Bob Krist's Secrets of Lighting on Location (an awesome book - I'll post a review soon).
These techniques are not necessarily mutually exclusive and there is some overlap. But awareness of these general strategies gives me a starting point for figuring out whether to use artificial light, by how much, and what modifiers I might need.