When designing small device displays, factors such as the size, contrast, and brightness of the display are frequently addressed. However, one factor that is often not given enough consideration is the impact of glare and reflections on visibility.
What creates glare and reflection?
The potential for glare and reflections is impacted by the viewing distances, viewing angles, luminance, reflectance, direct lighting, ambient lighting, and indirect lighting expected during use.
In controlled environments like an airplane flight deck, glare and reflection problems can be addressed by eliminating the source of the glare through adjusting or filtering the lighting conditions because they are part of the overall design (this is described in detail in areas of the Design CoPilot application). However, when addressing devices used in the home, lighting conditions are not under the control of the designer.
So, what can be done to reduce the likelihood of glare and reflections for these devices? Four areas should be considered:
- Display background
- Background and information colors
- Surface finish
- Cover position
First, consider the background of the display and whether its color and finish can be a source of glare or reflection. Large areas of bright colors with glossy finishes can be particular sources of glare and reflections. Whether or not there is backlighting of the display also impacts these considerations because the light can make everything more visible and increases the distinction between the information and the background.
Background and information colors
The combination of colors chosen for the background and displayed information can also be a source of glare or reflection. Presenting dark characters on a light background may reduce the effects of distracting reflections on a display in some lighting conditions. However, the opposite can be true in other lighting conditions. In terms of visibility, high contrast ratios are usually beneficial. However, too much contrast can create discomfort for the person viewing the display. For example, if images are significantly brighter than the background on which they are presented, the images may seem glaring and result in eye strain, discomfort, or fatigue. This is particularly true under low ambient lighting conditions. Contrast ratios should not exceed 15:1 in order to avoid increases in direct glare. Under low ambient lighting conditions, luminance contrast should be at least 10:1 but should not exceed 15:1.
The finish of the surface covering the display is also an important component to consider. Use a matte finish to reduce glare on surfaces surrounding the display. For example, labels, keys on the keyboard, counter drum surfaces and other surrounding surfaces should all have a matte finish to reduce the effects of glare. There is a trade-off to be considered for the material that directly covers the information regarding the transparency of the material and the potential for reflections and glare. A matte finished cover may not be as easy to see through, while a completely transparent surface can have a glass-like effect and result in a high potential for glare and reflections.
The consideration of the positioning of the display and the cover related to the information on the display can help to address this trade-off. Ideally, the display should be positioned to avoid reflection from ambient light sources, but with hand-held devices there is no control over the location of ambient light sources in the user’s environment. The angle of the display cover to the information can be adjusted to determine whether a particular angle reduces the likelihood of glare and reflections in the range of lighting conditions expected. The tilt angle should be sufficient to appropriately reduce glare but not so much as to greatly reduce the angular size of the display symbols.
I look forward to hearing about any experiences you have had and solutions you have developed for dealing with glare and reflections in hand-held devices. Also, stay tuned for upcoming posts in this series examining display visibility.