Bright Ideas

How Well Do You Know Kelvin?

Finally Bulbs June 15, 2017


With the advent of new and considerably more energy-efficient lighting technology, comes the ability to produce light in different “temperatures.” The lighting facts label on your light bulb packaging calls it “Light Appearance.” Thus, manufacturers now offer three main types of color temperature for light bulbs: Soft White (2700K – 3000K), Bright White/Cool White (3500K – 4100K), and Daylight (5000K – 6500K). Lower temperatures enjoy an amber – or warmer – hue; the higher the temperatures are whiter and bluer.

Many lighting specialists have produced helpful charts and illustrations to demonstrate temperature differentials, including, and

But what is Kelvin? Named after Irish engineer and physicist William Lord Kelvin, it’s a unit of measure for temperature based on an absolute scale which starts at absolute zero, the temperature, as Wikipedia explains, “at which all thermal motion ceases in the classical description of thermodynamics.” In other words, it’s really cold.

The Lord Kelvin experimented by heating a block of carbon. The carbon changed color as it heated up, going from a dim red, through various shades of yellow, all the way up to a bright bluish white at its highest temperature. With this scale in mind, today the color temperature of light bulbs are measured by spectroradiometers, which determines how many red light waves and blue light waves make up the light that’s emitted from the bulb.

Why do we care? “Color is extremely important, because it not only affects how we see — whether it is people or furnishings — it also affects the mood of a space,” says Carnegie Mellon professor Cindy Limauro in an interview with John Conti for The incandescent light bulbs we have enjoyed and since 1879 almost universally produce light at a temperature of 2700 Degrees Kelvin, or 2700K. The temperature that has since been dubbed “Soft White.” Professor Limauro notes that “most people prefer the warmer light, because if you have a cold light, that affects how you see the colors of the wall as well as the skin tones of people.” In fact, she goes on to point out, “extremely high color temperatures can disrupt people’s biorhythms . . . exposing yourself to artificial ‘daylight’ at night can hurt your sleep.”

So just go out and buy light bulbs that are 2700K, right? Well, no. The lighting facts label offers an approximation of the light bulb’s temperature. And the variation, though not numerically quantified on the label, can have a big effect on human perception of the light. Professor Limauro recommends that “you should experiment with bulbs in your home to get just the quality of light you like best.”

Just keep experimenting? How much money do you have in your budget to go out and buy a bunch of different light bulbs? We share your frustration. That’s why the Finally Light Bulb Company was created – for the sole purpose of replicating the incandescent light you love with technology that provides the energy-efficiency you need. Have you seen yourself in our warm glow? Give us a try. Buy your Finally Light Bulbs here.