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Filed under: Lighting •Production •Tips •Training •

Mysteries of Color and Light

Between January 2007 and April 2008 I consulted for Element Labs on the development of the Kelvin Tile. During that time I learned a lot about color and spectrum. Someone on the Cinematography Mailing List’s CML-Basics list asked a question about color rendition and broken spectrum lighting, which got me going on a riff that I will post here, with some embellishment.

The Kelvin Tile uses two LED packages, of three colors each, to create a very broad spectrum adjustable color temperature light.

Color is created when spectra of light striking an object are either absorbed or reflected. For example, lighting a green object with full spectrum white light will result in all the wavelengths of light that are not green being absorbed, while green wavelengths are reflected.

The visible color spectrum, courtesy of Wikipedia.

Certain lights, such as sodium vapor streetlights, are missing large parts of the light spectrum, because they work by electrically exciting gas mixtures that only emit light in very narrow frequency ranges. That’s why you’ll see very little color at night in a parking lot lit with sodium vapor lights: the white cars will appear orange, because sodium vapor lights emit mostly yellow-orange light and the white paint on the cars contains that part of the spectrum, but they don’t look white because the light’s spectrum doesn’t contain any of the other colors necessary to create white. (See “additive vs. subtractive” on the last page of this article.) And other colored cars, such as blue or green or red, will appear nearly completely black, because they absorb all of the orange-yellow light and reflect none of their own color back because it’s simply not present in the light. You can’t reflect what isn’t there.

The sodium vapor spectrum, courtesy of Wikipedia. Any color whose spectra fall into the gaps between these colors will not be faithfully rendered. And there are a LOT of gaps.

Fun fact: the City of San Jose, in which I live, uses low pressure sodium vapor street lighting in order to reduce light pollution that would otherwise interfere with the operation of nearby Lick Observatory on Mount Hamilton. The narrow spectrum of low pressure sodium vapor lighting can be easily filtered by astronomers as it doesn’t interfere with the spectrum of light that they are observing. I learned this because I shot the video at the bottom of this page as a freebee for Lick Observatory more than ten years ago. All proceeds benefit the operation of the observatory.

LED lights are tricky. There were, when I last studied them, two types: phosphor and dye. Phosphor LEDs emit a fairly broad spectrum of light, while dye LEDs emit very pure, very narrow spectra. Up until the Kelvin Tile was developed most LED lights used only phosphor LEDs, and they weren’t perfect: they emitted a little too much green, which is why most of those lights come with some sort of minus green gel for color correction. Their spectrum isn’t perfect but it’s good enough to convince the eye that it’s white light, although if you looked at two MacBeth charts side by side, one lit with an LED light with phosphor LEDs and the other lit with a tungsten light, you’d notice that some colors on the LED side were dull and lifeless compared to the tungsten side.

A graph of white light created by three dye LEDs, courtesy of Wikipedia. While this light will appear white to the eye, any object whose colors fall between the spikes will not be faithfully rendered.

Read on for more interesting spectral goodies…

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The Best of Stunning Good Looks Art Adams | 08/30 A directory of my best articles, sorted by topic. This entry is a guide to my best articles, sorted by topic. Enjoy!

LIGHTING STRATEGIES: Rough Guide to Illuminating a Bounce Card Art Adams | 01/29 Lighting a bounce card is easy, right? Right… IF you know the basics. Here they are. Is bounce light really just about aiming a light at a white card and walking away? No. There are a couple of tricks to getting the most out of your bounce source, and I can show them to you fairly quickly using…

LIGHTING STRATEGIES: Exploiting a Single Light Source Art Adams | 01/28 Sometimes all it takes to make a beautiful picture is placing one light—as long as it’s the proper light source. This still photo shows an example of one style of soft lighting that’s been in use for centuries, and for good reason: it works. There are few things more elegant than lighting a shot with a single light source. It doesn’t always work, but when it does—it’s magical.

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Great article! My brain melted, but I liked it.

Posted by ninjanels  on  03/26  at  11:06 AM

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Sorry about that. Is it the concepts or my writing that turned up the heat? If it’s the writing then I can work on that.

I’ve discovered that I like to feel my brain hurt. It’s fun learning about the hidden side of why things work.

Posted by Art Adams  on  03/27  at  12:12 PM

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This confirms some things I had suspected. One is that building your own lights using consumer florescent bulbs may result in gaps in the spectrum you’re using.

I’ve thought about using an inexpensive spectroscope to get an idea about the “spectrum density” (I made up that term but it sounds good) of various photographic light sources. I’ve found these two that might work:

http://scientificsonline.com/product.asp_Q_pn_E_3120400 $1.95

http://scientificsonline.com/product.asp_Q_pn_E_3053066 $5.95

Have you tried this? What do you think?

Peace,

Rob:-]

Posted by Rob  on  03/30  at  09:16 AM

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A quick question: if silver retention is done to the negative, what effect would it have on the shadow areas? Besides graininess, would the contrast in the shadow area be increased as well?

Likewise, a similar question: if done on the positive, what effect would it have on the highlight areas?

Cheers,
Derrick

Posted by .(JavaScript must be enabled to view this email address)  on  04/19  at  08:51 PM

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I think the section of this article relating to additive and subtractive primary colours helps to answer something I was wondering about a while ago: Why exactly does striking a positive print from a colour negative create a positive image?

I think that the answer lies in understanding which of these sets of primary colours balance each other out (R/C, G/M, B/Y?).

Unfortunately, right now my brain is frazzled so I’ll have to work it out later.

Posted by .(JavaScript must be enabled to view this email address)  on  06/05  at  10:27 AM

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Okay, I’ve figured it out. It’s very simple if I’m right, probably one of the first things you’d learn if you studied photography formally, but I’m self-taught.

What confused me is hearing and reading references by cinematographers to red, blue and green layers on negative film. I assumed they were referring to the colours of the dyes, which I suppose must be cyan, magenta and yellow on a negative - hence the colour of the image you see when you hold developed negative up to the light. It’s nice to put things together.

Excuse me for cluttering up your comments section.

Posted by .(JavaScript must be enabled to view this email address)  on  06/05  at  10:53 AM

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