Antiglare vs. Antireflection

Two terms used to talk about the impact of ambient lighting on displays are reflection and glare. The reduction of these is done using surface treatments for the display which are termed antireflection and antiglare.

Glare Defined

Glare is a phenomenon related to the difficulty of seeing in the presence of bright light such as direct or reflected sunlight or artificial light such as car headlamps at night.

Glare is caused by a significant ratio of luminance between that which is being looked at and the source of glare. Factors with significant impacts on the experience of the display are the angle at which the viewer is looking and the glare source itself as well as individual human eye adaptation. Glare can be generally divided into two types, discomfort glare and disability glare. Discomfort glare results in an instinctive desire to look away from a bright light source or difficulty in seeing a task. Disability glare renders the task impossible to view, such as when driving westward at sunset. Disability glare is often caused by the inter-reflection of light within the eyeball, reducing the contrast between task and glare source to the point where the task cannot be distinguished.

Relating to LCD monitors users, however, glare refers to the reflection at the display surface of intense or at least very noticeable light which is deemed by the viewer as being highly distracting. Often, a viewer will consider a noticeable reflection of let’s say a white colored shirt in a display as a ‘glare’ which reduces his/her ability to perform view the screen image adequately. This is more correctly defined as a specular reflection (see image below).

Specular reflection describes glossy surfaces such as mirrors or LCD cover glass, which reflect light in a simple, predictable way. This allows for production of reflected images that can be associated with an actual (real) or extrapolated (virtual) location in space. Diffuse reflection describes matte surfaces, such as paper or rock.

Antiglare Surface Treatments

Antiglare properties are produced by ‘roughening’ the surface of the display. This roughening can be done by any one of a number of innovative processes; be it mechanical design, chemical treatments or spray deposition. Chemical processes or spray treatment are the two most commonly used enhancement treatments of glare for LCD monitors. In the chemical process, the glass or polycarbonate overlay to be applied to the display is ‘etched’ with an appropriate solvent; then buffered with hydrofluoric acid (for glass) or an organic solvent (polycarbonate). This removes material in such a manner as to leave a microscopically roughened surface. Spray treatment involves spray or dip coating of the protective overlay with a unique solution which, on drying, will leave a roughened layer behind. A common method involves using a nano-particle suspension of SiO2 which leaves behind a random distribution of particles when dried. Subsequently, this surface treatment changes the ratio of specular to diffuse (Lambertian) reflections.

The degree to which this occurs is measured by a “glossmeter”. This instrument measures light intensity over a small range of the reflection angle. The intensity is dependent on the material and the angle of illumination.

Reflection Defined

The appearance of objects, their color and surface finish, which can be noticeably viewed as reflected image from the surface of the LCD monitor, and in many cases cause significant inadequate viewability. It can further be characterized by the way in which the LCD reflects and transmits light (visible part of the spectrum of electro-magnetic radiation).

LCD screen reflections have three negative effects: (1) they reduce the contrast of the displayed visual information by adding (reflected) luminance to the emitted luminance, (2) reflected white light reduces the saturation of displayed colors (bleaching), and (3) the image of light sources reflected in the screen cause the human visual system to focus on that image which is usually at a much farther distance than the information shown on the screen.

Antireflection Surface Treatments

In contrast to antiglare processes, antireflection treatments are usually in the form of very thin, multilayer films which are typically laminated to the surface of the protective overlay substrate, be it glass or polycarbonate material. Careful design of the film involves specification of the refractive index of the glass or plastic and of the surrounding medium (typically air). With this information, the designer of the film can make a determination of which materials to use and the thickness to be deposited. These films are able to reduce the specular reflectance of a surface from the Fresnel value (about 4% for glass) to less than 0.5% over the visible range.

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Optical Bonding Technical Description