Blue Hour

The sun has gone and the sky is still lit, so everything sits in a deep even blue with no shadows in it. The light comes from the whole sky at once.

It is the only time of day when the sky and the artificial lights of a city balance. Windows, street lamps and signs all read at the same time as the sky, which is why it is the standard slot for a city exterior.

The window is civil twilight, with the sun between the horizon and about six degrees below it. That is roughly twenty to forty minutes at mid latitudes, and it closes fast.

Light levels drop by several stops during it, so exposure moves while you shoot. The usual plan is to shoot the widest and most valuable shot first and let the rest follow the light down.

The sky is the source, so it is soft and shadowless, and it sits cool at around 10000K. Anything tungsten in the frame reads strongly warm against it, and that contrast is most of the appeal.

Use it for city establishing shots, for exteriors that have to look like night without losing the sky, and for any scene that is about the end of a day.

Avoid it for long scenes. There is not enough of it, and the level falls while you work.

Golden hour comes before it, with the sun still up, warm directional light and long shadows on the ground.

Look for shadows. Golden hour has them and they are long. Blue hour has none at all, because the source is the entire sky.

The sky comes back black and the shot is just night. Say the sky still holds light and reads deep blue rather than dark.

The second failure is a blue grade over a daylight scene. Ask for artificial lights just coming on and for cool even ambience with no shadows, so the time of day is in the picture rather than on it.