Luttieprinter lights explained: points, stops and colour timing
printer lights are how film labs balanced a print, in points. what a point is, why 12 points is a stop but a stop of exposure is 6–8, and how to use them.
printer lights are how a film lab balanced a print. instead of sliders, the colour timer set three lights (red, green and blue) that exposed the negative onto print film, each counted in points. davinci resolve still has printer-light controls because they're a fast, predictable way to balance an image.
what a point is
a printer point is a fixed step of exposure at the printer: 0.025 in log₁₀ units, which works out to a twelfth of a stop. twelve points double or halve the light reaching the print (wikipedia's definition).
why a stop of exposure isn't 12 points
this confuses almost everyone who tries printer lights for the first time. twelve points is one stop at the printer. but if the camera negative was a stop over- or underexposed, correcting it takes only about 6–8 points.
the reason is the negative's contrast. a camera negative's gamma is around 0.6, so one stop more light on set (0.3 in log units) only makes the negative about 0.18 denser. 0.18 ÷ 0.025 is roughly 7 points. how many points it takes depends on the stock, which is why timers learned their negatives.
adding light takes colour away
the direction is the other thing to get used to. printer lights expose a negative onto print film, so more light in a channel makes that part of the print denser, which means less of that colour on screen:
- more red light: less red, so the print goes cyan
- more green light: less green, so it goes magenta
- more blue light: less blue, so it goes yellow/warm
- all three together: darker overall (this is the "density" or "printer density" control)
once that clicks it's quick to work with. a shot that's too warm needs a point or two of red; a shot that's too magenta needs a little less green.
where you'll use them
- balancing shots in a scene. printer lights move the whole image evenly, so matching two shots is often a couple of points on one channel.
- fixing exposure before a print look. a few points of density puts skin back where the print wants it.
- grading film emulation. with a print stage in the chain, printer lights behave exactly as the timer's did, because the print curve is what gives each point its effect.
trying them
luttie's film engine has printer lights on its print stage, counted in the same 0.025 log steps, with "more light, less of that colour" built in. it runs in the browser and grading is free; exporting the result as a .cube lut is part of luttie pro. if you're new to print stages, what is film print emulation? covers why the print matters.