The term blue hour, derived from La hora azul in Spanish, or L'Heure Bleue in French, is a period of time just before the appearance of the rising sun or right after it sets. Blue hour is most commonly known for its romantic connotations and the stunning visual quality it brings to dramatic scenes in films and photography.
It’s the moment when the sky has a predominantly deep blue hue and the light is soft enough to emphasise the most of the dark areas of the scene, without requiring any additional light source. This is due to Rayleigh scattering, which is the scattering of light by particles smaller than the wavelength of visible light, the same process that makes the sky blue.
When the sun reaches six degrees below the horizon, it is no longer directly illuminating the ground, but it is illuminating the upper atmosphere. This is known as civil twilight. During this period of time, red light, which has a longer wavelength than blue light, passes through the atmosphere into space, while the blue light gets scattered and diffused.
In the morning, blue hour occurs just before golden hour at the beginning of civil twilight, which is around 30 minutes before the sun rises. In the evening, it occurs at the end of the civil twilight, just after the golden hour and starts roughly 10 to 15 minutes after the sun has set.
Blue hour photography is an easy genre to master as you usually do not have to worry about harsh lighting or shadows in your shots. Landscapes, cityscapes, and portraits are photography genres that work very well during blue hour as the soft overcast light can create an ethereal mood in your scenes.
If you are new to blue hour photography, here are some tips to help you get started:
If you are using a DSLR to capture your shots, try experimenting with High Dynamic Range (HDR) photography. An HDR image comprises of a number of shots taken at different exposure levels, which are then blended together during post-processing. Some Nikon DSLRs have a built-in HDR mode feature, where multiple exposures of a scene are captured and combined in-camera to form an HDR photograph.