good motoring
Drive carefully at dusk
H.Kishie Singh

Statistics have shown that the highest number of auto accidents happen at dusk. Dusk is evening when the daylight has faded but it is not completely dark. Strange, but true, it is easier to see in the dark than at dusk.

The reason is as follows: The eyes have two sets of light sensitive cells, like a camera, to measure light. The cells that work during the day are referred to as cones.

They specialise in colour and clarity for vision. In the dark the cells that take over are called rods. These are no help in detecting colour but the rods are capable of making the eyes 10,000 times more sensitive to the light available.

In the human retina, it is estimated that there are about 75 million cones and up to 150 million rods! These photosensitive cells, the rods and the cones, are found in most vertebrate animals. Informatively, the rat’s retina has only rods, no cones, which is why it is colour blind. With this information, it may not be a bad idea for Indian drivers to get their eyes tested. Considering that they are continuously driving though red lights, there is a chance they are colour blind!

Another strange fact, chicken retina has only cones, which is why it can’t see in the dark. If you have been driving during daylight hours and you won’t be home till late, you are going to face a problem at dusk. As the light fades, the cells starts to shut down. Cones need sunlight or a strong pair of headlights to help them keep alert. Manufacturers are aware of this problem and are constantly coming up with better lights like High Intensity Discharge (HID) or Xenon lamps.

So darkness is descending, and the cones go off duty! It is not completely dark and the rods have not been fully activated. Rods rely on contrast to be fully effective. The shadowy, hazy, soft light of dusk does not provide this contrast.

In any case, rods are slow to start work, like tubelights. They do not come on instantly. They rely on a chemical called "rhodospin," that is light sensitive. During daylight hours, the rods are switched off and the "rhodospin" lies dormant. For the "rhodospin to wake up," regenerate and go to work and provide vision can take time; may be up to an hour. If you have got a long drive ahead of you at night, it is recommended that at dusk you stop and rest with your eyes closed. When you open your eyes, the "rhodospin" will have had time to regenerate.

Also keep in mind, if you live close to the equator, the period of dusk is short. Suddenly it is dark. This demand for better vision is almost instant, whereas the regeneration of the rods will be slow. Drive with extra caution. In the upper latitudes the sun sets slowly, and this gives time to the rods to go to work.

Irrespective of where you live, dusk is the most dangerous time to be on the road. The truckers know of this problem only too well. At dusk they will pull into a dhaba. They take an hour-long break. Wash, dinner and rest, and by the time they move off, it is fully dark; the rods are at work. Vision will be at its best; the eyes have adjusted.

There is just one thing that can destroy this vision. The headlights on high beam of an approaching car. They put the rods out of action almost instantly, bring the cones out to work almost immediately. In a flash the car is gone by, leaving the eye confused and you, the driver, blinded. Even if it is for a second or two, it is the most dangerous moment of your life. The only remedy is not to look at the headlights; look away, or even close one eye. What would really help is if the drivers were to dip their lights. Unfortunately that does not happen. On the contrary, it is common to see cars with lights on high beam, fog lights on and may be a couple of extra lights on for good measure. And this would be in the Sector 9 market.

We know that dusk is the most accident-prone time. We also know that bright lights are a contributing factor to accidents.

There is not much we can do about dusk but there is something we can do about bright lights. Drive on low beam!

Happy motoring.