VarTech’s CCFL-enhancement – We Engineer Light

VarTech Systems specializes in the manufacture of high-brightness LCD display systems. Standard color LCDs are often unable to provide sufficient luminance for viewing under bright, outdoor environments; the result is poor image quality. VarTech’s high brightness monitors deliver a radically higher level of brightness, resulting in unparalleled picture sharpness. Our high-performance products are ideal for use under any high ambient light condition, and will give you the intensity and brilliance your application requires.

Our CCFL-enhanced products are commonly found throughout the following real world applications:

- Mobile transportation systems (automotive, marine & avionics applications)
- Industrial and medical systems
- Dynamic advertising (commercial advertising displays)
- Outdoor presentation systems (kiosks, drive-though ordering systems, etc)
- Sports facilities
- Military equipment

The display screen on a sunlight readable/outdoor readable LCD should be bright enough so that the display is visible under strong sunlight. Second, the display contrast ratio must be maintained at 5 to 1 or higher.

Although a display with less than 500 nits screen brightness and a mere 2 to 1 contrast ratio can be read in outdoor environments, the quality of the display will be extremely poor. At Landmark, a truly sunlight readable display is typically considered to be an LCD with 1000 nits or greater screen brightness with a contrast ratio greater than 5 to 1. In outdoor environments under the shade, such a display can provide an excellent image quality.

Luminance is the scientific term for “Photopic Brightness” which specifies the visual brightness of an object. In layman’s terminology, it is commonly referred to as “brightness”. Luminance is specified in candelas per square meter (Cd/m2) or nits. In the US, the British unit Foot-lamberts (fL) is also frequently used. To convert from fL to nits, multiply the number in fL by 3.426 (i.e. 1 fL = 3.426 nits).

Luminance is a major determinant of perceived picture quality in an LCD. The importance of luminance is enhanced by the fact that the human mind will react more positively to brightly illuminated scenes and objects. Users are typically more drawn to brighter displays that are more pleasing to the eye and easier to read. In indoor environments, a standard active-matrix LCD with a screen luminance around 250 nits looks good. However, a sunlight readable LCD with a screen luminance of 1,000 will look even more beautiful.

Contrast ratio is also a very important factor. Contrast Ratio is the ratio of luminance between the brightest “white” and the darkest “black” that can be produced on a display. Contrast ratio is another major determinant of perceived picture quality. If a picture has high contrast ratior, you will judge it to be sharper and the image significantly crisper than a picture with lower contrast ratio. For example, a typical newspaper picture has a contrast ratio of about 5 to 7, whereas a high quality magazine picture has a contrast ratio that is greater than 15. Therefore, the magazine picture will look better even if the resolution is the same as that of the newspaper picture.

A typical AM LCD exhibits a contrast ratio between 300 to 700 when measured in a dark room. However, the contrast ratio on the same unit measured under ambient illumination is drastically lowered due to surface reflection (glare). For example, a standard 200 nit LCD measured in a dark room has a 300 contrast ratio, but will have less than a 2 contrast ratio under strong direct sunlight. This is due to the fact that surface glare increases the luminance by over 200 nits both on the “white” and the “black” that are produced on the display screen. The result is that the luminance of the white is slightly over 400 nits, and the luminance of the black is over 200 nits. The contrast ratio then becomes less than 2 and the picture quality is drastically reduced.

VarTech’s sunlight readable LCDs with 1500 nits screen brightness will have a contrast ratio over 8 with the same amount of glare under the same strong sunlight, making the picture quality on these units extremely good.

Uniformity is another important factor relating to sunlight readability. Uniformity is the maintenance of luminance from one display area to the next. Non-uniformity can be viewed as a gradual shift in brightness from one area to the next on the display, making the display inconsistent and less pleasing to the eye. Most of the LCD manufactures specify uniformity by measuring the screen luminance at 9 points on the display.

At VarTech Systems, uniformity is measured as follows

Uniformity = (Lmax – Lmin)/ (Lmax + Lmin)

where Lmax (Lmin) is the maximum (minimum) luminance measured with a 10 mm diameter meter aperture over the LCD active area except the last 10 mm area from the edges.

VarTech’s CCFL-enhanced products consistently maintain a uniformity level of better than 20%.

All LCD backlights powered by cold cathode fluorescent lamps (CCFL) require inverters. An inverter is an electronic circuit that transforms a DC voltage to an AC voltage, which drives the CCFLs. VarTech’s CCFL-enhanced systems are equipped with high-quality inverters.

The dimming range or dimming ratio of an inverter specifies its capability of performing backlight luminance adjustment. For inverters used in notebook computers and LCD monitors, the backlight luminance can be adjusted typically over a dimming range of less than 10:1. That is, the luminance is adjusted from 100% down to about 10%.

For very high brightness backlights used within VarTech’s CCFL-enhanced sunlight readable LCD systems, the inverters must be able to provide a much wider dimming range. Otherwise, the LCD screen will be too bright during nighttime conditions. Therefore, our inverters provide a typical dimming ratio of 200:1, meaning that the luminance can be adjusted from 100% down to 0.5%.

Dimming capabilities are beneficial because lowering the backlight luminance will result in a lengthening of the backlight life. It also lowers the power consumption and the related thermal management issues.

One must remember, however, that any CCFL-enhanced high brightness backlight system will consume a significant amount of power, thereby increasing the LCD temperature. The brighter the backlight, the greater the thermal issue. Additionally, if the LCD is used under sunlight, additional heat will be generated as a result of sunlight exposure. Temperature issues can be handled through proper thermal management design. Thermal management information can be obtained through discussions with one of our technical sales professionals.

If power consumption and/or thermal management are of paramount importance for your project, perhaps our LED-enhanced technology would provide a better solution.