The human eye is incredibly complex and can control the amount of light that reaches our retina, to ensure we have optimum vision in both light and dark conditions.

Without going into the complex science, our retina contains tiny cells known as Rods and Cones, which are responsible for our vision Photopic (colour vision) and Scotopic (dark-adapted vision). We also have the clever ability to see with something called Mesopic vision, this is basically a fancy way of combining the other two, so we can see correctly during the transition between light and dark, for example, during twilight.

Dark adaptation is the process by which your eyes adjust to darkness after being exposed to bright light. It’s a natural process that involves the recovery of visual sensitivity in the retina after exposure to intense or prolonged light.

Broadly speaking…
• In light conditions, our pupils constrict to only allow in as much light as is needed for our cone receptors to enable us to see in colour.
• In dark conditions, our pupil dilates to allow as much light as possible to reach the rod receptors within our retina, which work in low-light conditions, enabling us to see in the dark.
Now, the reason we experience temporary difficulties seeing when we move from dark to light (temporary glare, causing us to slightly squint), and light to dark (the black hole effect) is because our Rods and Cones both have different reaction times to the change in light that we’re experiencing.

Therefore, it is especially important that artificial lighting is suitably designed to account for vision. Particularly, when considering the design of tunnel lighting. This applies to road tunnels and pedestrian tunnels.

Dark adaptation is very much at the forefront when designing lighting for tunnels.  It is important to ensure that the lighting inside the tunnel prepares the eye for the conditions that are to be experienced. This ensures that the ‘black hole’ effect and the daylight glare effect are minimised, helping our eyes adapt to the change in light levels, by making sure the two conditions are less extreme in comparison to one-another.

There are many reasons why we must ensure we consider adaption during the lighting design process, here at DFL we love the challenges that lighting pose and enjoy building the right solutions for our clients.”

Think you have a challenging project regarding lighting? We haven’t found one we couldn’t solve yet, so get in touch with me at ryan@dfl-uk.com