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Insight into Eyesight II - No light, no sight.
Why can’t people see in the dark?” asked the 7year old boy looking baffled. The time was about 2pm; despite the fact that the sun was up, it was cool – an ideal time for a walk. How would I explain this simple phenomenon to this little boy? I asked him in return, “What happens when you shut your eyes?”
“When you close your eyes, you shut out the lights and you see nothing,” was his intelligent response.This little boy probably knows more than I think he knows, I cautioned myself. “The weather is just right for a stroll. Let’s go out and enjoy somesunshine.” As we walked through the well laid out housing estate, I asked him to take note of the blue skies; the white clouds; the well-trimmed,lush green grass lawns; the dark green leaves and beautiful flowers and the coloured roofs of the houses. “Please pay special attention to the surface of the roads; the pot-holes and water puddles.” Why?” he asked inquisitively. “Just do as I say. I’ll explain later,” I commanded.
His attention was soon diverted. “Uncle, look at those exotic cars at the intersection,” he said, pointing at the row of cars.”What an unusual combination of colours!One is bright red with white stripes; another snow white and the third isgreen with a blue top.”I have never seen such odd combinations of colours in my life!” he exclaimed. I chuckled and muttered to myself,”Seven long years indeed!
After about 30 minutes out in the sun, soaked in sweat, we returned to the house, sat in the lounge and put on the air conditioner. I didn’t know when I was overpowered by sleep. It was about 8pm when Ade tapped me gently on the shoulder and said, “Uncle you are yet to answer my question, “Why can’t people see in the dark?”
“I thought that had been settled by your answer. Didn’t you say when you close your eyes you shut out the lights? So in the absence of light, there is no sight!”
I wasn’t surprised when he asked me, “What is light?” “You tell me,” I said throwing it back at him. Something told me he had been exploring the Internet in search of an answer while I slept. I was right. Without any hesitation, he replied, “Visible light is a form of energy which our eyes can detect. It is made of electro-magnetic radiation and travels in a straight path at a speed of about 300,000 kilometres per second.
Until recently it was said that nothing could travel faster than the speed of light.
However, the latest evidence suggests that this may be wrong. A bundle of visible light consists of light waves of different wavelengths. This is responsible for the different colours of light. There are three primary colours of light; Red has the longest wavelength, followed by Green and Blue with the shortest wavelength.Mixing them in various ways will make all other colours, including white.
“I am dazed by this little boy. Can anything travel faster than light? That’s news! I’ll take him up on that later,” I thought to myself.
“Ade, let us go for a walk again,” I requested and quickly added when I saw the look of disapproval on his face, “The answer to your question in out there!” As we stepped out of the house, PHCN struck plunging the whole estate into total darkness. The central backup generator took a long time coming on providing a perfect situation for the final stage of my simple experiment.
“Ade watch your steps,” I cautioned but too late to stop him from stepping into the water filled pothole. “Oh I didn’t see it,” he lamented. “I can’t see anything; the lawns, the leaves and flowers and even the coloured roofs are all black and indistinct. Look at those cars! They are all black.”
“You can’t see in the dark because light which falls on the surface of an objectis reflected into our eyes. Inside the eye it sets up a chain of reactions which sendssignals through the nerve at the back of the eye to the brain for interpretation. When it is dark, there is no light; no light falls on the surface of the object, no light is reflected and nothing is seen!Share