A giant nuclear reactor in the sky
Life on earth depends on the sun. Without it, we wouldn’t be here.
And it’s also of course a huge source of pleasure to most of us, as a million package holidays will testify.
It’s just a shame it’s so dangerous.
The harm the sun’s rays can do to the skin is well-publicised. But experts are equally concerned about the damage that sunlight can cause to the eyes.
Janice Acquah put her sunglasses on and went to investigate...
First stop was Professor Jim Barber’s garden.
Prof Barber is a photobiologist - in other words, a biologist specialising in the effects of light on life.
Sunlight, he explained, is in essence energy. Energy that in various ways enables life to thrive on earth.
There’s a visible spectrum of colours (that you can see separated when you look at a rainbow) and there are other types of non-visible radiation, such as ultraviolet and infrared light.
Ultraviolet (UV) light is the part of the spectrum that’s responsible for causing skin cancers. That’s because it contains very high energy radiation. "Much of it is fortunately filtered out by the ozone layer," Prof Barber explained, "but some does penetrate."
"We call that UVB. There’s also UVA, which is not as dangerous as B is, but can still cause damage to DNA, skin and other tissue.
So it’s very important to reduce the amount of that falling on your skin, by using sunscreen and other products."
So "Slip, Slap, Slop" as they say in Australia:
Slip on a T-shirt. Slap on a Hat. And Slop on the sunscreen.
But what about the sun harming our eyesight?
Everyone knows it’s dangerous to look straight at the sun - as the warnings surrounding the recent solar eclipse stressed again and again. Particularly of course with binoculars or a telescope - that would be crazy.
But it might seem surprising that after billions of years of evolution, the same sunlight that makes life possible, is capable of causing serious harm to the eyes even without us gazing at it for any length of time.
Next stop: St Thomas’s Hospital in London.
Using a slightly disturbing model of the eye, John Marshall demonstrated how human sight works.
"We can think of the eye as being in two parts," he explained. "At the front there’s the cornea and lens, which collect light and focus it on the light-sensitive areas at the back. And at the back there’s the retina, which is concerned with detecting an image and sending it to the brain. And both of these areas can be damaged by overexposure to sunlight."
The type of damage that can result from overexposure to sunlight depends on what type of radiation is absorbed, and where.
"For example, if you’re in a snowfield, where there’s a lot of sunlight being reflected up into your face and your eyes, you’ll get a stinging sensation known as ’snowblindness’. That’s caused by the UV radiation on the front of your eyes.
"If you get too much visible or infrared light, the damage is caused by the concentrating effect actually causing changes in the retina at the back of your eye."
Can you tell if you’ve damaged your eyes?
Yes ... and no.
If you sustain eye damage from UV light, you’ll know all about it in 8 hours time. An agonising burning sensation will overwhelm your eyes. But the good news is that it’s reversible. Every 5 days or so the cells on the surface of the eye are completely renewed.
However if you’ve damaged your retina, there’s no pain perception, and the only way you’ll know is because of some dysfunction in your vision. An optician will be able to investigate the condition further. But unfortunately if you have damaged the back of your eye, it’s permanent.
The two best ways to protect your eyes are:
1. Wear a hat with a brim - because this will keep your eyes shaded.
2. Wear sunglasses which protect from UV light.
But some sunglasses are far better than others, as Janice discovered when she spoke to John Mellerio of the University of Westminster.
"In a good pair of sunglasses, you need to think about comfort, good fit, strength of frame etc. But the important thing is the lens," he explained.
"And you have to find out how much UV the lens lets through.
Too much UV coming through can eventually cause a cataract to grow over the years ... and we think that the retina can be harmed over time by overexposure to light, particularly blue light."
He then assessed Janice’s sunglasses - but they didn’t get the green light.
The lens was good and passed the test for blocking UV light. But their size and shape bothered him...
"They’re too small. The UV light can still come in round the sides. You’d be better not wearing glasses like this at all, because if you squint at the sun," he said, demonstrating by screwing up his eyes, "you can cut out half or more of the radiation coming in. But you won’t squint if you’ve got your glasses on. You need a much larger lens - wraparound glasses are the best."
First broadcast: Friday 15 Oct 1999 on BBC TWO
To learn more about how to protect your skin and eye from the sun’s rays, here is a very small selection of the sites containing comprehensive and objective information:
Sun Exposure: Precautions and Protection - Safe Sun Tips for Adults
Safe Sun Tips for Kids
And if you want to know more, why not try one of our courses: Studying science with the OU