What is brightness?
Brightness is the scientific term for "photopic brightness," which specifies the visual brightness of an object. Colloquially, it is often called "brightness". Brightness is specified in candlesticks per square meter (Cd/m2) or nits. In the United States, the British unit Foot-lamberts (fL) is also frequently used. To convert from fL to nits, multiply the number in fL by 3.426 (ie 1 fL = 3.426 nits).
Brightness is a factor in the perceived image quality in LCDs. The importance of brightness is heightened by the fact that humans respond more positively to bright screens. In an indoor environment, a standard active-matrix LCD with a screen brightness of about 250 nits will look good. In the same situation, an LCD with a brightness of 1,000 nits or more looks amazing.
What is Contrast (CR)?
Contrast ratio (CR) is the ratio of brightness between the brightest "white" and the darkest "black" that can be produced on a monitor. CR is another influencer of perceived image quality. If a picture has a high CR, you would consider it sharper and clearer than a picture with a lower CR. For example, a typical newspaper image has a CR of around 5 to 7, while a high-quality magazine image has a CR of greater than 15. So even if the resolution is the same as the newspaper picture, the magazine picture will look better.
A typical AMLCD exhibits a CR of about 300 to 700 when measured in the dark room. The CR on the same unit measured under ambient lighting is greatly reduced due to surface reflections (glare). For example, a standard 200 nit LCD measured in a dark room has 300 CR, but will be less than 2.0 CR in strong direct sunlight. This is because surface glare increases the brightness of the "whites" and "blacks" produced on the display by over 200 nits. The result is just over 400 nits for whites and over 200 nits for blacks. Then the CR ratio becomes less than 2 and the image quality drops sharply and is unacceptable.
What is perspective and why is it important?
The viewing angle is the angle at which the image quality of the LCD degrades and is unacceptable for the intended application. Perspectives are usually referenced in horizontal and vertical degrees, the importance of which depends on the specific application. When the viewer physically moves to the side of the LCD, the image degrades in three ways. First, the brightness drops. Second, contrast usually drops at large angles. Third, the color may change. Most modern LCDs have acceptable viewing angles, even when viewed from the side.
For LCDs used in outdoor applications, defining viewing angles based on CR alone is not sufficient. In very bright ambient light conditions, the display was barely visible when the screen brightness dropped below 200 nits. Therefore, the viewing angle is defined in terms of CR and brightness.
What is a true sunlight readable or outdoor readable LCD?
First, the display on a sunlight readable/outdoor readable LCD should be bright enough so that the display can be seen in direct or strong sunlight. Second, the display contrast ratio must be maintained at 5 to 1 or higher.
While a display with a screen brightness of less than 500 nits and a contrast ratio of only 2:1 can be read in an outdoor environment, the quality of the display will be so poor that it will not be able to get the desired information efficiently. A true sunlight readable display is generally considered an LCD with a screen brightness of at least 1000 nits and a contrast ratio greater than 5:1. Such a display can provide excellent image quality in shade in outdoor environments.
What is NIT?
NIT is candela per square meter (Cd/m2. For LCD monitors, it is the brightness of the display's front panel. NIT is a good basic reference when comparing brightness between monitors. Most desktop LCD screens or notebooks Computer LCD screens have a brightness of 200 to 250 nits. These standard LCDs are not readable in direct or even indirect sunlight when washed off.
How do I know how much NIT is required for my application?
Applications will vary based on the location of the LCD and the amount of ambient light that can cause the display to fade or become unreadable. As a rule of thumb; laptops and desktop LCDs are typically used in offices with light conditions in the 200-250 nit range. For indoor use with uncontrolled or indirect sunlight, a 500 - 900 nit monitor is recommended. If the application is outdoors or in direct sunlight, at least 1000 nits and above should be considered.
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