Day for night is a cinematic technique used to simulate a night scene while shooting in daylight. It is used mainly because film stocks and camera sensors lack the sensitivity in low light conditions to capture night scenes without the use of artificial light.

Although shooting day for night has become less common in recent years due to the improvement of cameras and film stocks, not every filmmaker can afford to use artificial lights in the wide exterior scenes like the one below from Tarantino’s Django:

When does day for night work

Another reason for using day for night technique is when we need to shoot exteriors in the city during blackout. As an example, we can have a look at the film 28 days later. The night scenes were shot during the day for three reasons:

1. The filmmakers weren’t allowed to use Mackintosh Muggleton at night time
2. There is supposed to be total shut down of all power in London – every building must appear light-less. It would be too complex to remove the city lights in post.
3. The director Juan Carlos Fresnadillo prefers to shoot day for night to create ghostly quality and a sense of unease for the film.

Source

Day for night technique works great for all the exterior shots in the wilderness where the only source of light is the moon.

Why do nighttime scenes are tinted blue

Although moonlight is not actually blue, it appears bluish to our eyes due the Purkinje effect. Most of the films tend to tint night scenes towards blue colors and it’s one of the key ingredients of faking day for night scenes – either in-camera or in post.

Examples from movies

Mad Max: Fury Road

This nighttime sequence was actually filmed in the Namibian desert in bright daylight, but was then transformed into a blue environment by colorist Eric Whip based on a suggestion made to production by Jackson to film the sequence overexposed  – instead of the traditional underexposing for day for night – by two stops or more.

Here at vfxguide we can read interesting approach to day for light:

I had talked to John Seale about it and they did a test in broad daylight in the middle of the day – full sun – and shooting with the ARRI at various exposures,” recalls Jackson. “I came along to that, and said, ‘Oh you’re doing the over exposed thing,’ and they said, ‘Don’t be silly’. I think they were doing half a stop over. I was proposing to do four stops for a test, at least, with one, two, three and four stops over. I had to work hard to convince them to do a test at four stops – they just thought it was ridiculous. But then we did a test on location and the overexposed ones looked amazing and it was solved right there.

Heat

The below picture is a very well known frame from Heat and on the right is my attempt to grade it back to normal. Of course the quality is poor due to the source material quality, but it shows clearly that the process can be reverted to a certain point.

The Proposition

I tried the same thing with a frame from The Proposition where day for light technique was used, and again, it’s quite convincing how the frame might have looked before the post production process:

Quick test and grading in Resolve

Here I wanted to show you a short clip from one of my projects where I used the mentioned technique. Here’s the before and after:

The important aspect is soft lighting. The catchlight shows a window that might fake the moonlight coming in.

Here’s the screenshot showing the wheels in DaVinci Resolve:

This is all I did to get the end result – dropping the gain and pushing the colors toward blue-teal.