Are the bright lights that cyclists now use safe for the eyes of onlookers? (continued)
鈥� A previous answer (25 August 2018, p 57) stated that an LED beam isn鈥檛 harmful to eyes because it contains 鈥渁 lot of light but almost no heat鈥�. But this contradicts the concept of conservation of energy. When light energy hits your retina, it is converted into heat 鈥� and LEDs produce a lot of light energy.
It is true that an LED radiates a lot less light than would be experienced in ordinary daylight, but it is the concentration of it that is important. In daylight, light is spread over the whole surface of the retina, so it isn鈥檛 very concentrated. An LED has a tiny emitting surface, and if this is focused onto your retina, the entire power of the beam is concentrated on a very small area. So, because much of the light energy is absorbed and converted to heat, this can potentially cause a localised heat spot.
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Looking directly at a high-brightness LED that isn鈥檛 fitted with a diffuser . If stared at for too long, it is potentially as hazardous as a low-power laser beam.
David Gibson, Leeds, UK
鈥淪tared at for too long, a very bright LED is potentially as hazardous as a low-power laser beam鈥�
鈥� If cycle lights are dazzling people, then they are badly adjusted. The beam should be directed away from the eyes of other cyclists. Cars with dazzling headlights would fail a roadworthiness test, but for some reason, cyclists tend not to be penalised at present.
Very bright flashing lights can be quite dangerous, especially on unlit country roads. Cyclists in some areas have been asked to avoid using flashing lights for fear of triggering epileptic seizures in observers.
Keith Oldham, Lancaster, UK
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