Posts tagged ‘eyesight’
By Chad Upton | Editor
Like many kids, I didn’t like vegetables — especially carrots and broccoli. Adults frequently told me that carrots would improve my eyesight, so that seemed like a good reason to try liking them.
There was one person who didn’t tell me this, he actually told me the opposite. My grand father overheard somebody tell me that carrots would improve my eyesight and he let me in on a little secret — it was all a big lie. Carrots do not improve your eyesight.
Sure, carrots and many other foods do contain beta-carotene, which metabolizes into Vitamin A and everyone agrees that is essential for maintaining eye health, but it does not improve it. If you are not consuming enough vitamin A, any number of sources could help restore your vitamin A supply. Carrots themselves are not unique or magical in this way. In fact, carrots have less beta-carotene per 200 calorie serving than red peppers, kale and lettuce.
If lettuce, kale and red pepper have more beta-carotene than carrots, why do carrots get all the eyesight credit?
If you’ve shopped for an HDTV, you’ve probably seen something on the spec sheet called “contrast ratio.” Contrast ratio is the difference between the darkest and brightest picture a TV can produce. Contrast is important to a good picture.
That’s because our eyes can recognize a contrast difference of 1,000,000,000:1. That means, the brightest thing our eyes can see is a billion times brighter than the darkest thing. Good contrast to your eyes is like a gourmet meal for your taste buds. Contrast adds a lot of detail to the picture and ultimately immerses you in the action.
Unfortunately, when shopping for TVs, contrast ratio is almost meaningless. It could be really useful, but all of the manufacturers measure this number differently and then call it the same thing — it’s really only useful when comparing two TVs from the same manufacturer.
Imagine you want to buy a new car: you are cross shopping three manufacturers who measure fuel economy in three different ways. The first one, measures fuel economy while driving down a hill, while the other two measure it on flat land and while driving up a hill. Obviously, you can’t compare the results of those tests. But, if you’re looking at two cars from the same manufacturer then there is some comparative value to those numbers, even though they may not be accurate in a typical situation.
Thankfully, our eyes are extremely sensitive to contrast. Turn both TVs on and look at a flat black image for a while. A flat black image makes it easy to spot variations in darkness (aka “banding”), no banding should be present in a good TV. If you still can’t tell the difference and they both look good, then the difference is too small to worry about. Trust your eyes, they are incredible instruments.
It takes 20-30 minutes for your eyes to adjust from one extreme to the other because the contrast ratio is so high. If you’re in bright sunlight and then walk into a very dark room, it will take 20-30 minutes before you can see your best in that room. If you are in a moderately bright room and go into a very dark room, it is often closer to 15 minutes.
The rods and cones in your eye are tested during dark adaptation. Rods are more sensitive to light and take longer to adjust. Cones are much faster to adjust, often in approximately 9 minutes. People over the age of 50 need twice as much light to see as well in the dark as a 30 year old. So, if you need more light, consider my CF light secret.
Frequent fliers will eventually notice that the aircrew dims the airplane’s interior lights on final approach during night landings . They want your eyes to be adjusted to the darkness outside in case the landing does not go as expected and you have to evacuate the plane.
Written By: Chad Upton
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