Why does the brightness of road tunnel lights change in intensity and colour in some tunnels as you drive further in. A tunnel I went through tonight started with very bright yellow lights as I entered, then transitioned to dimmer white lights by the time I got to the end of the tunnel.

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Why does the brightness of road tunnel lights change in intensity and colour in some tunnels as you drive further in. A tunnel I went through tonight started with very bright yellow lights as I entered, then transitioned to dimmer white lights by the time I got to the end of the tunnel.

In: Technology

It’s supposed to make the transition from outside to a darker tunnel less dangerous by giving your eyes time to adjust.

It’s a safety feature.

When you go into the tunnel, it has to be so bright inside the tunnel that you automatically perceive it as well lit up. This bit is more important during the day when you can have trouble seeing anything inside a tunnel that is too dark, but matters at night too.

In the middle of the tunnel, there is really no need for that much light, so it’s dimmed down. Or simply regulated by installing the fixtures further apart.

As you reach the end of the tunnel, the light is gently toned up again. Well. During the day, that is. Because when you have been inside the dim lit tunnel for a while it’ll be difficult to adapt to the brightness of full sunlight outside again.

If you look carefully, you notice that even a tunnel in an area with no street lights at all got some streetlight or a while right before and right after the tunnel. To make the transition easier for nighttime drivers.

You can do pretty advanced stuff with this if you really want to, but all it takes is that you have a bAW set of fixtures in the tunnel that operate at a fixed rate and a handful around each opening that you either dim or turn on and off depending on the readings of a lux meter just outside the tunnel.