Kelvin Scale for Production – Part 1

It is not my intention to make this a history lesson on where the Kelvin scale originated-there is plenty of info on the Internet to do that on your own-but to apply the scale to production and how to “trick” the viewer’s eye when using the info on set, or in photography.

The best information that I could find on setting this up can be found at the following link:  http://www.3drender.com/glossary/colortemp.htm

It would be helpful to read through 3DRender’s info and then come back to proceed and I thank them for their advance work.

GRAPHIC: color temperature conversions

Check out the chart of gels and their color temps here: http://www.rosco.com/us/filters/roscolux.cfm#colors

TITLE: Winter Lake

I shot this last winter behind our house.  Were it not for the snow-it was actually not a sunny day but a bright one-this would look more like a summer day.  The darker exposure (I under exposed this shot by about 1 1/4 stops) and the fact that I shot it at 4000K makes you believe it is a cold, winter day.

Perhaps you learned this in school but forget it.  In my case I probably didn’t pay attention that day because I couldn’t connect with the application.  Perhaps you didn’t learn it at all.  If that’s the case, it’s time to go back to school!  Everyone on the visual end of production should have at least some knowledge of the Kelvin scale, always referred to on set as “K” when used with a temperature such as “32K”, short for 3200 degrees Kelvin.  Generally speaking, most of what we do on a film, video or photography set revolves around the standards, 32K or 55K, each short for 3200 degrees Kelvin (tungsten or incandescent) and 5500 degrees Kelvin (average outdoor light on a sunny day)  But variations of that are where the magic happens!

My first experience with this was when I was hired as a PA only months out of school on a spot that was being shot on 16mm film for a Mexican food restaurant in Houston named Ninfa’s, short for the very successful entrepreneurial, Hispanic woman, affectionately referred to as “Mama Ninfa”.  Mama Ninfa started her first restaurant in 1973 and then opened a larger restaurant in 1976 in Houston that became an instant success.  This spot was filmed in her Houston home on a dark, dreary, cloudy, rainy day.  However, this Christmas spot, which revolved around a phone call of a hypothetical friend or family member who lived up north, called for Mama Ninfa to talk about the sunny, warm Christmas in Houston.  It was mesmerizing to me how the director used light to “trick” the audience into believing what he wanted them to believe.

First of all, they built a box of c-stands and speed rail outside of her kitchen window.  Then, with a 5,000 watt HMI (also called a 5k but not to be confused with what we’re talking about here), from outside, they focused the light on the exterior of the window. (HMI has become a generic term for all lights that fit the Hydrargyrum Medium-arc Iodide family.  Their color temperature, while it can and will vary, is generally between 5,500 and 6,000K, or 55K and 6K)  A 5K has a pretty good punch and so it punched through the curtain and window quite nicely to create what looked like beautiful sunlight blazing through the window.  So, instead of the dreary 4k (4000 Kelvin), cloudy light coming through the window, from the inside of the house, the director created a convincing shot.  By the way, he then further warmed the light up a bit by filtering, or gelling, the light with 1/2 CTO (color temperature orange) to give the light an early morning look.  This is the magic that I want to address…filtering.

If you set the color temperature on your camera to 32K, you are shooting what? An indoor scene that could be lit by “practicals” or existing lights in the home or business where you are shooting, and probably enhanced by or exclusively lit by incandescent fixtures such as any lighting instrument that puts of a light balanced at, or around, 32K, your Lowell or ARRI kits, for example.  What always amazes me is how easily the mind is tricked.  If you light an indoor scene, camera is balanced at 32K, and you put an instrument in the background, hallway or “blowing” through a window that is balanced for 56K, at just the right intensity, your mind reads the scene to be shot at night, even though it may be broad daylight outside.  It is the 32K light against the 56K light that makes your mind think it’s night and that takes place when you know how to “treat” your lights so that you accomplish the desired effect.

If you spend much time watching old black and white westerns, you’ll notice that they almost always had a night shot that was in fact shot outside.  Lighting instruments in the early film days were huge and weighty so a lot of lighting outside, especially in some of the remote locations where they shot, made artificial lighting prohibitive.  If you look closely at those scenes, you’ll notice the hard shadows that no moon would ever make unless you were very, very fortunate to be shooting on a very bright, moon lit night.  Never happened.  What they did was shoot day for night by under exposing their shots to varying degrees.  When color came along, they typically shot these scenes with a film stock that was color balanced for tungsten to give the final result a bluish look, or they filtered their camera lens with varying degrees of blue filter.  Again, by under exposing and tinting blue, you accomplish “day for night.”

In a similar way, you can treat you lighting instruments.  If you are starting with a tungsten instrument (balanced for 32K) and you need for it to fill outside or be a key light source outside, you will need to filter your instrument with a full CTB (color temperature blue) filter, and if your camera is set to 55K, you will be able to shoot the scene as if an exterior scene.  You will also find gel to accomplish varying degrees of that.  For example, if you want to shoot at 56K, because you are shooting outside, and you want to create sunlight in your scene, that may not exist, you can gel your tungsten light with 1/2 or 1/4 CTB.  This would cool your light down but not to the extent that it would take you all the way to 55K.  So, in effect, you could create sunlight on a cloudy day when it didn’t really exist.

Again, the color conversion chart…

GRAPHIC: color temperature conversions

This also holds up in photography.  When shooting stills, I never leave me camera in “auto” white balance mode.  It’s unthinkable.  But that is so because I have a firm grasp of the Kelvin scale.  I want to choose what time I place the viewer at the site where I’m shooting, and I’m able to do that by tricking them to believe whatever time I want it to be, early morning, late afternoon, etc.