Hey everyone, it's Joey again. I hope you enjoyed learning about lumens in the last post, and this week I'd like to add two new terms to your arsenal of lighting vocabulary.
COLOR TEMPERATURE and CRI
Well, that's actually two words and an abbreviation, but we will consider them two terms nonetheless.
Color temperature is a concept that is often misleading but certainly present everywhere we look when it comes to lighting. What it means, in essence, is that a color temperature is the color of light emitted by a black body object as it's heated to a certain temperature, measured in degrees Kelvin.
What's a black body object, you ask? Well, the term refers to an opaque (not transparent or translucent) object that emits thermal radiation. An example would be the filament of an incandescent light bulb. However, a filament is often slightly grey, so it's not considered a 'perfect' black body object.
Getting back to color temperature, imagine that incandescent filament gets heated, just a little bit. What happens? It starts to glow, usually orange. Add more heat (or more power to the bulb via a dimmer), and it glows yellow. Add more heat and it glows white. This concept and system of measure, is how we determine color temperature.
If you look at the chart below you will see how color temperature relates to colored light, and how common sources of light fall on the spectrum.
Generally speaking, what's considered 'warm' light falls under the 3000K area, and what's considered 'cool' light is above it. So, a fixture at 6500K is going to give off a bluish bright-white light, and one at 2400K will be a glowing yellow (how we verbally classify colors has little to do with their actual color temperature).
Now, you may be thinking "Wait a minute, I have seen fluorescent bulbs that say 6500K on them that are certainly not hot to the touch, as opposed to my 2400K 60 watt candelabra bulb that can literally bake a cake if it's held close enough. What gives?" Well, my insightful friend, that is why the color temperature scale we use today is often referred to as the "Correlated Color Temperature" or CCT. It refers to the color emitted by a tungsten filament, but doesn't require that it be the light source. A tungsten bulb emitting 6500K is going to be WAY hotter than one emitting 2400K, it's true, but that would not be efficient and would also be dangerous. That said, any light source can match a color temperature without actually reaching that temperature.
However, not all light sources can do that magical matching without some sacrifices, and those sacrifices are rated in CRI. CRI is the "Color Rendering Index" of a light source, and it measures how faithfully a light source can reveal all colors in an object as compared to the king (or queen) of all light sources - the sun. The best CRI rating is 100. Incandescent bulbs with those trusty tungsten filaments are often high-CRI fixtures, as they burn a single element to produce their color temperature--though they are energy hogs and can burn you quickly. Fluorescent bulbs, though they are more energy efficient and can match color temperature well, are often lower on the CRI scale as they burn different types of phosphor to develop their color temperature. As a result of this mix of sources, certain colors are not rendered well, and certain objects just don't look pleasing under the light emitted. You simply can't experience the full beauty of an object under a light source that can't display all its colors. That's why many people (myself included) do not like fluorescent lights, as unfortunately most places using them don't spring for the more-expensive-but-far-more-pleasing full-spectrum high-CRI models.
What about green?
You might have noticed in the chart above that there are some colors missing from the color temperature spectrum. We know, for example that LEDs like ilumi can produce 16million+ colors. Well dear readers, what we are talking about now is wavelength, and that will be covered in the next post.
I hope everyone has a Happy Holidays, and take note of the relative absence of the color blue on the dinner table. There's a reason for that, and we'll cover that in another post as well.