Video Terminal Glasses

What Are VGs?

American Opticals new VGs (Videoterminal Glasses) are occupational eyewear designed specifically to reduce glare and reflections in the video display terminal (VDT) environment, and improve contrast as seen on the VDT Screen. In addition, these lenses absorb more that 99 percent of ultraviolet (UV) radiation.

VGs are available in magenta, grey and blue, for use with VDTs having green, black-and-white and amber displays, respectively. They're available in prescription and non-prescription versions, as well as, each meeting the requirements of ANSI.1- 1979.

How Do VGs Reduce Glare and Reflections and Improve Contrast?

Glare may be defined as the presence of bright light sources in the field of view, which compete for one's attention and thus are distracting or worse, a cause for discomfort. Glare sources include fluorescent lights, exposed incandescent lights, windows, light reflected from metallic or light-colored objects, etc. (Figure 1). VGs reduce the intensity of light from these sources- making them less distracting and the VDT operator who wears them more comfortable.

VGs also help to improve the intensity contrast of the video display. They achieve this by reducing the intensity of both the text and the background. Although the percentage of reduction is the same in each area- approximately 20 percent- to the VDT operator wearing VGs, the brightness of the background appears to have been reduced by a greater percentage than the percentage by which the brightness of the text appears to have been reduced. This is because , as Figure 2 graphically shows, brightness is not a linear function of the intensity of the light reaching the eye 20% reduction in background intensity. Reduction in background brightness: .08. 20% reduction in text intensity. Reduction in text brightness: .02

The background of a VDT screen is not absolutely black, for several reasons: Its phosphors reflect ambient room light; the outer surface of the glass covering the VDT screen specularly reflects images of light sources or bright objects; light emitted from the phosphor is internally reflected the glass, creating a "halo" around each character of the text. The reluctance of light from the screen is often referred to as "glare." Although special screen, anti-reflection surfaces and diffusing surfaces are available to help reduce these reflectances, they cannot be totally eliminated. VGs reduce low-intensity screen reflectances and halos by the same physical principle that accounts for the improved contrast between screen text and background, noted above. (Figure 2).

Not only do VGs impart greater intensity contrast between the VDT screen text and background, by control of the spectral properties of transmitted light they impart greater color contrast. For example, when magenta-lens VGs are worn by a person operating a VDT with a green emitting phosphor, the test, still vividly green, is seen to appear against a background having a blue-red cast- rather than grey or green-grey.

 Each of the features described above should help VDT operators who didn't wear eyeglasses as well as those who do. But ordinary eyeglasses can cause additional problems for VDT operators-- problems which are significantly diminished by VGs.

The lenses in ordinary eyeglasses produce reflections that can interfere with the VDT operator's clear view of the display screen. these arise from a variety of sources.

Depending on the specific conditions, these reflections can produce actual ghost images or an overall veil of light which interferes with or reduces the contrast on the VDT screen. The surface reflectance of American Optical's VG lenses is some 60 percent less than that of ordinary eyeglass lenses. This reflection reduction is a significant benefit to VDT operators who ordinarily wear eyeglasses. In addition, it obviously enhances the advantages that VGs offer those VDT operators who do not require corrective eyeglasses.

Although studies to date do not indicate that UV radiation causes specific problems for VDT operators, VGs have been designed to eliminate more than 99 percent of the near UV (320 to 400 nm) radiation.

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