Glare and over lighting are at the core of the problems dealing with visibility lost with outdoor lighting. Glare occurs when bright, direct light hits your eye. If you can see the source of the light or the light reflector, it’s producing glare. A good light will shield the bulb so that you see a lit area below the light instead of a dazzling light source. There are two basic types of glare.
Discomfort glare doesn’t necessarily prevent you from doing what you want to do, but does cause constant adaptation of your eye to the varying light levels. That in turn causes discomfort and reduces your ability to see. This is especially dangerous when you need to focus your attention on driving and don’t need to have your ability to see reduced by lights alongside the highway.
Disability glare may literally blind you, because the human eye adjusts itself to the brightest object in sight, which then limits its ability to see other things. If there’s a big difference in light intensity between the lit area and the surroundings you won’t be able to see either very well.
Glare and Safety
Either type of glare severely diminishes our ability to see properly in the nighttime environment. Visibility is improved with minimal, shielded lighting combined with reflective signs and road markings. Safety should demand that the best visibility possible is provided after dark.
If you walk or drive away from a brightly lit area into a darker area or vice versa, it takes your eyes time to adjust. During that adjustment period visibility is hampered. A example where ones visibility might be impaired could occur as one exits an overly lit commercial area and enters a highway with just ones headlights for lighting. It takes a few minutes for your eyes to adjust to the darker conditions of the highway. Another example from a different perspective might occur in the transition period from exploring a cave to exiting where there is a bright light. A transition area with very dim lights would allow ones eyes to adjust before moving into a brighter area.