If you carry a handheld computer, tablet, or laptop outdoors or during work, the ability to clearly see the content on the screen for practical use is crucial.

This depends on many factors, such as outdoor brightness, presence of glare, screen size, clarity and contrast, viewing angles, and more. Experts calculate the "effective" contrast in bright outdoor light by estimating the ratio between sunlight and the light reflected back from a typical computer screen (which uses various treatments and includes multiple reflective layers). The effectiveness of controlling these internal reflections determines the screen's readability in sunlight.

For current display technologies, the importance of the backlight is equal to, or perhaps even greater than, that of the backlight itself. A strong backlight is usually better than a weak one, and I say "usually" because an overly strong backlight can make the screen look dim. This happens when black pixels cannot block the backlight that is too strong for a specific screen technology. Of course, a strong backlight will drain the battery faster.

Nevertheless, backlight intensity is critical for readability outdoors and in sunlight. But what exactly constitutes a "strong" backlight?

Quantifying light has never been easy. In the past, everyone knew that a 100-watt bulb was bright, a 60-watt bulb was moderate, and a 40-watt bulb was best for places where some light was needed but not too much.

But that was before the brief era of "100-watt equivalent" spiral fluorescent "bulbs" and today's LED lights, which are still sold by their wattage equivalent to old incandescent bulbs. LED bulb brightness is also measured in lumens (and sometimes lux). Calculating the meaning of lumens ("the total amount of visible light emitted by a light source") and lux ("a unit of illuminance") is overly complex and practically useless in real life. So, as long as people remember how bright a "real" 100-watt bulb is, new technology bulbs are likely to be sold by their watt "equivalent".

What does this have to do with backlights? Not much. It's just that describing backlight intensity is as complicated and confusing as describing light bulbs. So, how to deal with it?

Essentially, the unit for the light emitted by a display's backlight is candelas per square meter (cd/m²). A candela is both the average brightness of a candle and, according to the Google Dictionary, "the luminous intensity, in a given direction, of a monochromatic radiation source emitting at a frequency of 540 × 10¹² Hz, where the radiant intensity in that direction is 1/683 watt per steradian". That's it. Now calculate it per square meter. Sigh.

Given this apparent complexity, some in the industry have suggested abbreviating cd/m² as "nits". So 100 cd/m² becomes 100 nits. Maybe "nit" is short for "unit". No one seems to know. Nowadays, many display specifications include the nit level.

Even technically savvy people often confuse luminance and illuminance. Illuminance refers to the amount of light falling on a surface. Luminance is what we measure as the brightness of a surface that is lit by light. So, for our purposes, the light source behind the screen illuminates the screen. The brightness of the surface caused by this light source, i.e., its illuminance, is measured in nits.

How bright is one nit? Or 100 nits? 100 nits is equivalent to 100 candelas per square meter. Imagine a 3 x 3 foot square area with a hundred candles lit underneath it. How bright would that be? I don't know. So perhaps it's better to think about what things produce an average of how many nits, and use that as a reference. A standard laptop has a brightness of about 200 nits. A good tablet or smartphone has a brightness between 500 and 600 nits. Rugged laptops can reach up to 1500 nits, as can modern 4K HDR TVs.

What makes everything more difficult is where we view the illuminated surface. Even a laptop with a brightness of 180 nits can look bright and clear indoors. But outdoors, the same laptop is almost unreadable. That's why we emphasize in our specifications that our AOZORA rugged tablet series is equipped with sunlight-readable screens, and we also indicate the brightness of our screens. This information can be found on our website: www.aozorawireless.com

So, for better or worse, if you want to know the screen brightness of a handheld device, tablet, or laptop, look at its nit value.