In the early days of wildlife filmmaking it was pretty much impossible to record the nocturnal activities of animals and plants because cameras were simply not sensitive enough to record in low light. Viewers, filmmakers, and even scientists remained in the dark about the hunting activities of many of the world’s top predators. Whatever approach filmmakers use to reveal nocturnal events is going to be a compromise, and that’s just because it isn’t possible to see in the dark.
Filming dusk for night / day for night
A technique used to overcome this was filming "dusk for night" or "day for night". The effect is achieved by a combination of camera settings and grading techniques to crush the images and make it appear darker than was actually the case. This was only deemed acceptable if the behaviour filmed was what usually happened nocturnally.
Nowadays, this technique is rarely used as technological advancements (infra-red, low-light, starlight cameras etc.) allow a variety of true night filming techniques to be employed. "Day for night" grading may still occasionally be used by editors, but only to provide close-ups and cutaway shots, that allow the film's story to flow, or when filming at night is too dangerous.
This technique was used to film the polar bears in Earth’s Greatest Spectacles. The extreme sub-zero night time temperatures of the Arctic winter are not only a challenge physically, but camera equipment constantly fails and it would have been too great a risk for the crew to have filmed the polar bears at night.
Infrared cameras and thermal imaging
Only with the development of infrared cameras and lighting equipment did wildlife filmmakers finally have the tools to record natural animal behaviour at night, in pitch darkness. Infra-red light has wavelengths over 700nm (nanometres), making it invisible to the eyes of humans and many other mammals. Infra-red cameras can detect reflected infra-red light, recording behaviour we could not see with the naked eye. The Planet Earth team made the most of this technology to film lions hunting elephants at night, which can be seen below.
The main drawback of the original infra-red cameras was that they could only record good quality images in the areas lit by the infa-red lights, so the filming area was limited in size. More recently, thermal cameras have widened the scope of night time scenes that can be filmed. Thermal cameras record infra-red radiation emitted by objects, detecting the slightest differences in temperature and processing this data into a "heat picture" or thermal image. The Great British Year revealed the secret night time drama of an ordinary field with this technology, the clip of which is below.
Thermal cameras capture real events, but often in a very artificial looking way. Surprisingly, the "day for night" technique resembles more closely how you would see something with your own eyes.
Image intensifying technology
Another approach to filming in low light is to amplify the light there is using image-intensifying technology. This new technology can reveal what is happening in landscapes after dark, so long as there’s moonlight and/or starlight.
The Africa series used a specially designed image-intensifying camera called a "starlight camera" to record a nocturnal gathering of rhinos. The resulting footage below shows rhinos in a whole new light.