This is a beautiful time in Massachusetts – the leaves are changing, pumpkins and mums are appearing in many yards and on many porches, and color is everywhere. The change of season also brings with it a change in the amount of daylight, which most of us view with a bit of melancholy. But this change in daylight brings possible dangers that many of us do not realize.
We use different parts of our eye to see at different light levels. During the day, our eyes use cones to process light. Cone photoreceptors are located primarily in the macula of our retina (there are cones outside of the macula but not many) and are used to create our color vision of the changing leaves. These densely-packed macular cone cells also provide for our sharp, clear vision.
In the evening and in darkness, most of our vision is processed by using our rod photoreceptors (also used for our peripheral vision) because low light levels are not strong enough to stimulate our cone cells. When it is getting dark, our eyes are changing from predominantly using cone vision with sharp acuity to instead, relying on vision from our rod photoreceptors. Therefore, our visual perception falls somewhere between our sharp daylight vision (called “photopic vision”) and our fuzzy vision in relative darkness (called “scotopic vision”) and is called our “mesopic vision.”
As the daylight hours shorten in the fall, we find ourselves commuting and traveling at times when we are using our mesopic vision. This can be dangerous, as the difficultly with mesopic vision is that we often have a false sense that we are seeing more clearly than we really are. In addition, the sun at this time of year is rising and setting near or during commuting times, causing glare issues that can also make travel more difficult.
Here are some suggestions to be safer at this time of year: