The science behind glare suggests two main sources. 'Direct glare' is when brightness (such as the sun or a lamp) is directly visible. When brightness is visible as a reflection it is 'indirect glare'. These two glare sources can both lead to contrast glare.
Glare is bad for you physically and it reduces your performance. Your eyes are an amazing feat of biological engineering; however, just like most cameras, they adapt to the brightest light source and can’t deal with large contrasts in light. When your eyes detect extreme brightness, everything else can appear darker, including any electronic screens you are using, making it difficult to see details.
Of course, when faced with challenging light levels, your eyes don't simply give up. They try to adjust to the contrasting light levels, making tiny eye muscle adjustments to minimise glare. The cost of this continuous adjustment is eye muscle fatigue, which leaves them feeling tired, strained and sore. It’s a familiar feeling if you've ever spent a bright, sunny day squinting because you forgot your sunglasses. Similar discomfort can occur when using electronic screens in situations where there is glare – and not just blinding sunshine, lower levels of glare can cause discomfort, too.
So, day-to-day, check for glare when you areusing an electronic screen. Direct glare is easiest to spot: look up, down or to either side of the screen you're viewing and if you encounter a contrasting light source from a lamp, or unfiltered daylight through a window, it's pretty likely you've got some direct glare to deal with. Your three tools for direct glare are to reflect, redirect or filter. Shade, filter or move any exposed lamps so direct light is not in the same field of view as your screen. The same is true for windows. If you can't shade the daylight, don't position yourself and your screen with a window in your field of view (it’s best to have windows at your side).
Indirect glare can be harder to spot. Check your screen first. Is it glossy? Are there any reflections in it? If you can see any of the lights in the room reflected in your screen, then you might be experiencing indirect glare. The same is true if your screen reflects the sun, or gives you a mirror image of the view out of the window. When your screen is affected by indirect glare it can be hard to see what's on it. It's a bit like shining a torch onto it. Indirect glare can also be caused by light reflecting off other surfaces in your field of view, such as a shiny desktop, a mirror, a glass picture frame, a clock. If you take a moment to look, you might be surprised at the ways in which light sources bounce around your room.