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What is Candelas Per Square Meter?
Tulie Finley-Moise
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January 3, 2020
Computers are only getting smarter and as the digital age continues to evolve and surprise, and the technology that comes with it is bound to leave you scratching your head. Better yet, your curiosity could lead you straight to your favorite web-connected device and into the depths of the internet to get some quick education on whatever burning questions you may have. Even as you journey toward the answers you’re looking for, your eyes brighten from the screen you’re engaging with.
It’s thanks to powerful LCD and LED screens that you’re able to engage with your selection of smart devices. You’ve likely grown accustomed to having the ability to freely adjust the brightness on any number of your smart devices. And as simple a modification as this dimming may be, the technology behind it is surprisingly complex.
Using this guide, we’ll walk you through the basics of luminance, how it’s measured, and where and why it matters. First, let’s define a couple of the terms.
What is a candela?
A candela (cd) is the measure of light intensity in a given direction. It is the unit of luminous intensity as prescribed by the International System of Units. One candela is about what a common wax candle gives off, which explains the fact that this used to be referred to as candlepower until units were standardized in the middle of the 20th Century.
So, 1 cd is what a candle gives off as viewed from a certain direction. Surprisingly, distance from the light source plays no part in the measurement of luminous intensity. The same light intensity can be seen from any direction that is not obscured or blocked in any way. So a 25-watt lightbulb, which has 135 cd, will be visible from 135 times farther away than your single wax candle.
What is a lumen?
Lumens refer to the total amount of visible light a device produces. A higher lumens value means there is a larger area that is lit. Say the candle that we just saw above at 1 cd shines in all directions - 360 degrees. It would give off 12.57 lumens (lm). That’s the total light in all directions from 1 cd. But if you blocked half the bulb, while you would still see 1 cd from the side not blocked, the total lumens would drop to 6.28 lm because the total light emitted overall was cut in half.
What is luminance?
So if candela means light in a given direction and lumens is total light, then what is luminance?
Luminance is the measurement of brightness perceived by the human eye. The world around you is perceived within a varying pattern of luminances both naturally and artificially lit. In fact, you’re experiencing a set degree of luminance as you read this on your computer or mobile device screen. In essence, luminance is the measurement of the brightness of light emitted from or reflected off of a surface.
Candelas per square meter
There are several unit terminologies that are used to measure and express luminance. The official International System of Units (SI) unit for luminance is candela/square meter (cd/m2). This is the most commonly used expression of measurement of luminance.
Nits
Nits are another standard unit of luminance that are used to measure a multitude of light intensities. 1 candela per square meter is equivalent to 1 nit. Nits are more commonly used in the United States than they are throughout the rest of the world.
Brightness
Unbeknownst to most, there is a distinct difference between luminance and brightness. Luminance measure the luminous intensity projected on a given area or in a given direction whereas brightness is a subjective attribute of light perception. For example, two computer monitors can be adjusted to have the same luminance, but the two cannot be objectively measured to have the same brightness.
What is candelas per square meter in tech?
The candela per square meter (cd/m²) is the standard unit of luminance used by tech manufacturers across the world. At HP®, we use candelas per square meter to inform you of the brightness capability of the HP monitors or HP laptops in our collection.
Because computer displays are generally used in indoor settings, they require a specific range of luminance measuring anywhere between 40 to 300 candelas per square meter. Ultimately, viewability is important in determining which laptop screen or desktop display is best for you.
Generally speaking, consumers typically look for impressive lumen specs rather than candela specs, but candela output is far more important when it comes to choosing a smartphone, tablet, computer, or even a flashlight. Lumens are frequently mistaken as the unit of measurement for brightness, but cd/m2 is actually the proper measure of luminance.
How to convert candelas per square meters
Outside of nits, there are three alternative ways to measure and express luminance. We won’t go into these in this article, but we will give you a guide to see how a single candela per square meter converts into other luminance units.
Candelas per square meter to footlamberts
A footlambert is 3.4262590996 times the luminance of a candela per square meter.
- Unit definition: (1/π)cd/ft2
Candelas per square meter to lamberts
A lambert is 3,183.0988618 times the luminance of a candela per square meter.
- Unit definition: (104/π)cd/m2
Candelas per square meter to stilbs
A stilb is 104 times the luminance of a candela per square meter.
- Unit definition: 104cd/m2
Why does brightness matter?
How often do you stop to think about the reasons why brightness is important. If you’re like most people, you hardly ever think about it because brightness is simply everywhere. However, when it comes to modern technology that comes to life through LED and LCD screens, brightness is of the utmost importance.
From smartphones and televisions to display monitors and smartwatches, your favourite devices are getting brighter and brighter with every passing year. To gain a better understanding of how candelas per square meter factor into your everyday life, we’ll use a few common examples to paint a picture.
The average movie theatre screen can get as bright as about 50 cd/m2. Pre high-definition resolution televisions ranged anywhere between 100 and 400 cd/m2 whereas modern HDR TVs can output as many as 1,500 cd/m2.
With each passing year, tech manufacturers are engineering devices that feature brighter screens with higher candela per square meter measurements. While you may not notice the change in upgrading from one device to the next, you may notice a change in image clarity and sharpness. That is because brighter screens deliver more vibrant pictures and higher dynamic ranges.
Technologies like full-array local dimming, Micro LED, and quantum dots only work to continue this brightness trend and reshape the modern face of digital screens. This trend toward higher candelas per square meter effectively works to transform the images on your screen of choice into sprawling life-like images that astound with realism.
Recap
Let’s do a final unpacking and recap of the confusing and complex terminologies we covered.
- Candelas per square meter: Objective unit of measurement of luminous intensity
- Nit: Synonymous with candela per square meter; 1 nit = 1 candela per square meter
- Candelas: The measure of light emitted from a surface in a particular direction or at a particular angle
- Lumens: Total amount of light emitted by a device
- Luminance: Total brightness from a device and reflected surface
