Most people underestimate how much light a pair of sunglasses blocks out. A typical dark pair removes around 80 to 90% of the visible light reaching the eye.

Safely looking directly at the Sun requires reducing the light reaching the eye by a factor of around 100,000, meaning roughly 99.999% must be removed. Ordinary sunglasses can let around 10,000 times too much visible light through.

That is especially important on Wednesday 12 August, when the Moon will pass in front of the Sun, creating a deep partial solar eclipse across the UK. Timings and the amount of the Sun covered will vary by location. In Bristol, the eclipse begins at about 6.17pm and reaches its maximum at around 7.12pm. Viewers in Cornwall will see roughly 95% of the Sun covered.

Sunlight can injure the eye without causing pain or any obvious warning at the time. Solar retinopathy occurs when intense light damages the retina, the light-sensitive tissue at the back of the eye. Symptoms can appear several hours after exposure and include blurred or distorted vision or a dark patch in the centre of your sight. Many people........

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