Technique: Ratios between natural and artificial light

Transition periods of natural light when the light is constantly changing is probably one of the best situations when interesting outdoor photos can be created. A transition period is typically when the light is fading more and more in the case of post-sunset light or getting more and more intense as in pre-sunrise. Taking outdoor pictures in such conditions, however, presents some challenges to be overcome to get the most out of the good light. One specific such consideration is ratios between natural light and artificial light, i.e. the ratio of light intensity between e.g. a street light and the sky. This ratio is crucial to convey the message you want. A very intense natural light in relation to any artificial light sources makes the artifical light more or less disappear. An extreme example of this is photographing in mid-day, when the sky is at its brightest, when the light from a light bulb will be almost invisible (a ratio of 1:0). The other extreme is at night, when the sky will be near completely black and any artifical light will be the only light (a ratio of 0:1). Between these two we have our transition period, and the ratio will gradually change under such transition, something we need to watch when creating a photo.

The two photos below show this in action. The sunset was at 15:08 the day of the shooting. The upper photo was taken at 15:37, when the ratio was approximately 3:1 (the natural light was three times as intense as the artifical light from the streets lights and windows). Only 30 minutes later from the same location, the lower picture has quite a different ratio, closer to 1:1 (the intensity from the natural light from the sky was approximately the same as the street lights and windows). One thing is clear, the photos are quite different in both appearance and in the feelings they provoke. Which one is the better? Well, that would depend on what you want to say. Wanting to convey the message of a glitzy Grand Hotel in Stockholm I personally prefer the lower, with 1:1 ratio, for its deeper colors and fuller reflections in the water (due to the equal light ratios).

Grand Hotel in Stockholm at 15:37, about 30 minutes after sunset. Approximately 3:1 ratio.

  

Grand Hotel in Stockholm at 16:05, about 1 hour after sunset. Approximately 1:1 ratio.

Of course, much of the 1:1 ratio qualities can be achieved in post-processing of the upper photo, but for example the intense water reflections will be a challenge to recreate to look natural, not to mention all the time needed in front of the computer instead of being out shooting.

This short tech article only touched photographing landscapes with a combination of natural and artificial light, but the ratio thinking applies to any types of lights (even artifical vs artifical, as in the studio or flash vs natural light). So, next time you are out photographing in a transition period of natural light, with artificial lights in the scene, think about the light ratios, and I bet you will be surprised how much closer the photos are to your vision.