Looking directly at the Sun during an eclipse can be very dangerous.
You won't experience any discomfort or 'black spots' at the time but without adequate eye protection permanent eye damage or blindness can occur - even when up to 99% of the Sun's surface is obscured.
Only during complete totality is it safe to look at the sun without protection. (In fact, not only is it safe, it is truly an overwhelmingly and awe-inspiring experience best viewed without protection. Just be ready to look away or use a solar filter at the first sign of the returning sun!)
Two different damaging effects can occur when a person looks too long at the Sun.
Intense visible light triggers a series of complex chemical reactions within the retinal cells which damages their ability to respond to a visual stimulus, and in extreme cases, can destroy them - particularly the light-sensitive rod and cone cells.
On the other hand, near-infrared radiation causes heating that literally cooks the exposed tissue at the back of the eye.
Thermal injury or photocoagulation can occur, creating a small blind area. Loss of visual function can be either temporary or permanent, depending on the severity of the damage.
Most importantly, the danger to vision is significant because photic retinal injuries occur without any feeling of pain (there are no pain receptors in the retina), and the visual effects do not occur for at least several hours after the damage is done. [Pitts, 1993].
We strongly recommend the use of properly designed solar filters to remove these dangers. A protective viewer removes harmful heat and ultraviolet radiation, and reduces the visible brightness by a factor of 100, 000, making it perfectly safe to view the sun during any period of eclipse or normality.
Sunglasses do not provide adequate protection, as they do not block the wavelengths of light which are likely to damage your eyes, or reduce the intensity of the visible light sufficiently. Various other ad-hoc solar filters, such as welder's goggles can be used, but please, be sure you know exactly what you are doing. The cheapest and safest way to ensure your safety is to use eclipse viewers specifically designed for that purpose.
EclipseViewers UK's safety commitment to its customers
EclipseViewers UK only provide products which carry details of UK-conducted safety certification for conformity with Council Directive 89/686/EEC relating to personal protective equipment.
All products are accordingly also marked "Safe for direct solar viewing" and display statutory instructions for use.
All products carry the mandatory "CE" mark indicating conformity to European Directives, especially on Health and Safety.
EclipseViewers UK verifies printed safety certification details of acquired products against copies of BSI/INSPEC Certificates.
All viewers are provided in a protective wrapping to minimise the liklihood of mechanical damage.