Blue Hour

The time when the sun has dropped below the horizon, leaving no direct light, only skylight, so the whole scene is bathed in cool blue. It happens just after sunset or before sunrise. Shadow contrast is low, so light feels like it comes from nowhere in particular. The warm time while the sun is still up is golden hour.

The scene seen at an angle from above. The sun is below the horizon and does not shine directly, and a single warm, streetlamp-like light sits above to the camera’s left.

Camera view. The whole scene is steeped in blue skylight, and a warm light from the side lights one side of the bunny.

How it feels

Stillness
Loneliness
Dreamy
Calm
End of the day

When to use it

The moment city lights start to come on
People in a field, heading home after work
A street as the streetlamps switch on
Scenes that close out a day

In the movies

Jaws (1975) · Source: Movieclips (YouTube) · Original video

Days of Heaven 1978
Cinematographer Néstor Almendros wrote that many scenes were shot during the "magic hour" after sunset and before night, opening the lens wider and wider as the light faded. He described this window as about 20 minutes.

Not to be confused with

Golden Hour: The warm amber light while the sun is still up. Shadows are long, with a clear direction.
Overcast: Overcast days have few shadows too, but it is gray daylight with the sun up. Blue hour is blue light after sunset.
Day for Night: Shooting in daytime to make it look like night is a separate technique.

Prompt

Keyword

blue hour

Descriptive

Blue hour. The sun has just set, soft cool blue light fills the scene, city lights begin to glow.

Try these combinations

Wide shot + blue hour: a city lighting up
Wide shot, blue hour ambient light, cool 8000K color temperature, soft diffused illumination, a city skyline as the lights turn on
Medium shot + blue hour: a figure under a streetlamp
Medium shot, blue hour, a lone figure under a warm street lamp, cold blue night tones