A Light Education: Kelvin, Temperature, And Color Rendering Index (CRI) October 14, 2016 00:00

The light bulb aisle has never had more variety in choices for consumers than there are today.

Incandescent, fluorescent, halogen, and LEDs are all available, each with their own measurements in watts, lumens, life hours, and loads of other categories too.

Frankly, it can be a bit overwhelming at times and many people end up simply guessing on which product to get, only to be disappointed by the result when they screw it in at home.

That’s why in order to make the best decision on how to light your living space, you need to be informed about what each of these categories mean, especially when it comes to color temperature, Kelvins and Color Rendering Index.

Color temperature: from warm to cool

One term that you might have heard thrown around the lighting world a bit is “color temperature” and it’s a pretty important to understand. The phrase was originally used to describe the color of a heated filament and as a result the kind of light it produced.

To explain, if a filament found in your typical incandescent bulb was heated to a certain temperature, it might appear to turn yellow. As that temperature is increased, so too would the color temperature of that filament, turning whiter and eventually bluer in the process.

Fluorescent and LED lights on the other hand don’t really have a filament to heat up so they use the Correlated Color Temperature (CCT) scale, where light color output is matched to what color a material, such as a filament, would turn at a certain temperature.

For the most part, you’ll probably only see a combination of both of these scales, as shown below, to indicate a particular bulb’s color temperature. Incandescent bulbs for the most part stick to the lower range and fluorescents tend to be located more on the blue end of the spectrum.

Certain LEDs on the other hand, like most of the Flux Smart bulbs, enable you to choose between 16 million different colors, giving you the ability to switch between warm and cool lighting whenever you want.

That means it’s up to you to decide if your home should be lit with the soft, warm light that resembles traditional incandescent bulbs or bright, cool light to bring out your home’s little details.

Kelvins: the color temperature measurement

Now that you know a little more about color temperature, let’s dive a bit deeper into the spectrum introduced above.

As you can see, the scale changes from red and yellow light on the left to white in the middle and finally blue all the way on the right. This transition could be described as moving from warm light to white light to cool light.

As you can also see, there are some numbers below that correlate with the colors above, ranging here from 1800K all the way to 1600K. These measurements are a more detailed way to describe color temperature, with lower numbers being warm and higher cool, and are presented in K, units of measure that represent temperature based on the Kelvin scale.

Although Celsius and Fahrenheit are the king and queen of the temperature world, Kelvin is another way that temperature can be measured. The numbers above then are the actual temperature, in Kelvin, that a filament or other material would need to be heated to in order to produce the corresponding color light.

That means that in your typical incandescent bulb, the filament is probably around 4600 degrees Fahrenheit, or about 2810 K, when the light is on. And while LED and fluorescent bulbs produce very little heat, their light would be equivalent to a filament being heated to over three times higher than that!

So, as interesting as all this might be, how exactly does knowing about Kelvin help you pick out a better bulb for your home? The benefit of knowing exactly where on the color temperature scale a bulb fits means you’ll be able to pick out just the kind of light you’re looking for.

This comes in especially handy when bulbs are described as “warm” and “cool” since these terms are relative and there are no real designations for where warm lighting ends and cool lighting begins. Knowing precisely where it fits on the scale makes lighting your home the way you want even easier.

Color Rendering Index (CRI)

Knowing a bulb’s color temperature is an important part of ensuring your home has the right feel. If you are after a more modern décor, then a cooler temperature light might be for you. If you’d rather give your home a warmer, comfier feel to it, your best bet would be lights on the lower end of the color temperature scale.

And if you don’t have the color changing capabilities of such smart bulbs as the Flux Smart Bluetooth LED then you especially need to pay attention to each bulb’s Kelvin measurement.

But there’s another light bulb quality that can be equally critical to making sure your home gives the impression you’re after, and that’s Color Rendering Index (CRI). The CRI of a light bulb is basically a measurement of how well the light source shows an object’s color. It’s a scale from 1 to 100 with 100 showing colors at the same level as daylight (considered a perfect color preserver) and lower levels indicating some color vibrancy might be lost when shown in that light.

Consider, for example, the pictures above. This is a representation of what it might look like to shine a light with 100 CRI on a bowl of fruit versus what it might be like to shine a light with 50 CRI on the same bowl. You’ll notice that the colors in the picture on the right are far more muted than those on the left.

Now, obviously we all would like our colors as vibrant as possible and one benefit of the incandescent bulb is that it’s CRI is always a 100. Fluorescent bulbs on the other hand are markedly lower, with typical cool white bulbs having a CRI of around 60. LEDs will measure in a bit higher with CRIs ranging anywhere from 80 to 95.

One important note about CRI is that it is in no way related to the color temperature of a bulb but is rather dependent on the spectrum of the light it gives off. That means two bulbs with a color temperature of 10000K might look completely different in your living room, which is why you always want to be sure to check each bulb’s CRI to get a better idea of what to expect.

Let us know what you think

How do you decide what temperature light to use? Have you noticed the difference between a high and low CRI? Let us know in the comments below and be sure to check out Flux Smart Wifi and Flux Smart Bluetooth LED Light Bulbs.