Wednesday, February 5, 2020

Light Temperature

Artificial light is rated according to its color temperature, listed as a Kelvin number (Celsius degrees). 

When you heat up an incandescent filament, it radiates light. At lower temperatures, the filament gives off a more orange or yellow light. As it gets hotter, the color it radiates becomes bluer. 

Comparison of light temperatures via Reddit
When you buy a bulb, it is rated on this scale. In this photograph, a series of bulbs are lined up in a gradation from 1000 K to 10,000 K. Although the scale was created based on incandescent light, it is used for LED and fluorescent light as well.

A candle flame is about 1900 K. Bulbs that produce light at 2-3,000 K are often called "warm white" in the industry. White, neutral sunlight is rated at 5,000 or 5,600 K. Studio north light is closer to 6500 K and above that, the pure blue sky can go all the way up to 10,000 K.

This scale can be confusing or counterintuitive for artists, because the bluish paint colors that we call "cool" are associated with the light that is emitted at higher temperatures, while "warm" colored light comes from cooler sources.
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Wikipedia: Color Temperature

6 comments:

GJ said...
This comment has been removed by the author.
Drake Gomez said...

When I outfitted my studio with new lighting a few years ago, I researched lighting temperatures. To my surprise, many artists recommended lights in the 3000-4000K range, rather than the neutral 5000-5600K, which can make colors feel cool. There's also something called the "color rendering index," which is a scale from 0-100 that indicates how accurate colors appear under a given bulb. There's a nice LED bulb from Greenlux with a 90 CRI rating at 4000K.

James Gurney said...

Drake, thanks for that. I just refitted my studio with Waveform Lighting's 5000 K LED bulbs (24 of them), which replace the 4 foot fluorescent tubes I had before. They require only a third of the electricity, and the Color Rendering Index on those is 95, and the light quality is fantastic. https://store.waveformlighting.com/products/full-spectrum-t8-led-tube?variant=29398989144166

CerverGirl said...

Thank you for sharing what you use and like. The choices have overwhelmed me at times, and I haven’t known where to start.

markmors said...

I was going to ask if you ever used Ott lights--but I noticed your response about the other brand.

Choubbi said...

Hi James,
In your first sentence, you say "Kelvin number (Celsius degrees)".
Temp√©rature in Kelvin is the temperature in Celsius degrees shifted by approx. -273°C, in order to have its zero match the absolute low temperature (273K = 0°C, 0K=-273°C). BTW, the reason why we don't say Kelvin degrees but just Kelvin is because that unit starts at the absolute zero.
Otherwise a good clear post about color temperature, thanks.