An Imaginary Conversation about White Point and Digital Displays

An Imaginary Conversation about White Point and Digital Displays

An Imaginary Conversation about White Point

If you are reading this article, it is probably safe to assume you are at least tangentially interested in large-format digital displays – Nanolumens is after all a large-format LED company. One of the topics we have focused on in this space in recent months is the clarification of various display industry specifications. These specs can confuse even the sharpest AV insiders so with that in mind we’d like to dive into yet another spec to see if we can’t clear it up for you.

You know how your phone changes the tint of your screen from a crisp blueish light to a softer beige glow once it enters night mode? What your phone is doing is adjusting its white point in response to the changing of its user’s environment. What does white point mean? Below, we’ll get to the bottom of that by asking and answering a series of questions that will hopefully make this rather dense topic at least somewhat digestible.

So what is white point?

White point is the term used to reference the appearance of white on a screen or surface. It is also called color temperature.

Why is this a thing?

Simply from seeing how your phone changes its white point at night you can see that “white” isn’t always “white.” Theoretically, a true white exists but it is not something we can see in reality. So things that claim to be white, like a piece of printer paper, or the screen of a phone, computer, or digital display, all have their own levels of white. The white level on a piece of paper is dependent on the environment it is in since the paper itself is only reflecting light. The paper is always “white,” but that white looks different in sunlight than it does indoors. An LED display however, which creates its own light, has a white level that you can adjust yourself. Where you set this level affects the appearance of your display’s entire color profile, as a blueish white point will result in cooler, blueish content while a softer reddish white point will result in softer reddish content. These levels of white are measured in degrees Kelvin.

Like the temperature scale?

Yes. Let’s give a little backstory. In the late 19th and early 20th centuries, a scientist named Max Planck studied the way cold, black objects emitted different wavelengths of light as they were heated to varying high temperatures. Through his observations he was able to determine which wavelengths were associated with which temperatures. At the highest temperatures, the black object would glow blueish. Temperatures slightly below that prompted yellow, orange, and red glows as the temperature decreased (while still remaining very hot).

That didn’t answer my question

Since Planck was using the Kelvin scale to measure the temperatures he was heating his black object to, he used the temperature reading on the scale to refer to the colors the object emitted. At, 6500°K, he observed a distinct blueish white light. At 5000°K, a softer reddish white light. These temperatures became the de facto names for these colors, hence the term “color temperature.”

I associate yellow as being a warmer color and blue being a cooler color but it seems the color temperature for blue is higher.

Correct. While we perceive red and yellow colors as warm and blues as cool, that is more of a human association than a scientific correlation. Think of a lit match: the hottest part of the flame is the blue part at the center while the red and yellow flecks are slightly cooler (again, while remaining very hot).

So how does this circle back to white point?

As we’ve established, LED displays are set to a specific white point that informs how all its colors will be portrayed. In other words, when the screen is told to show white, the white point is the color it shows. Since the exact color of any given white point is hard to standardize or measure with words, it is done using the Kelvin color temperature. The most common color temperature setting for digital displays is 6500°K, also known as D65. This does not mean that the display itself rises to 6500 degrees Kelvin, just that the color it has as its white level matches the color produced by Planck’s black body at that temperature. This is almost certainly the white point setting for your phone and television.

So most digital displays use D65 as their white point but what about the other white points?

5000°K (D50) is the traditional white point for graphic arts work that will eventually be translated to print as it matches more closely with the common lighting conditions under which people typically read print content. Regular sunlight has a white point that ranges from 5000°K to 6000°K. Adobe Photoshop often has an internal default setting of D50 as well.

So summarize this for me please

Digital displays can adjust their setting for displaying the color white. This setting dictates which version of the color white will be shown when the display is told to show white. It informs the way all other colors are displayed as well. This is called the display’s white point. It is referred to by its color temperature, which is measured in degrees Kelvin, a remnant of Max Planck’s work observing the colors emitted by black bodies when heated to varying temperatures. 6500°K, also called D65, is the most common white point for digital display technologies. That should tie everything together nicely. Got it?

Got it.

Awesome. If you’d like to learn about any other LED specs, take a look at our latest white paper, ”Hey! What’s Does This Spec Mean?”

 

 

2020-02-13T13:15:06-05:00