>
>> >>> >>>
>>>> >>>>> >>>>>
>>>>>> >>>>>>> So why isn't red, yellow, etc as easy to see? If you wear a bright
>>>>>>> red tshirt, you aren't as visible as wearing a hi-vis jacket. Does
>>>>>>> it convert all the wavelengths into one or something?
>>>>>>
>>>>>> Not all, but some. It's fluorescent:
>>>>>>
>>>>>> The current standard that sets the requirements for high-visibility
>>>>>> clothing is EN ISO 20471:2013, under the PPE Directive 89/686/EEC.
>>>>>> This replaced the previous standard, EN 471:2003, in 2013. In >>>>>> addition
>>>>>> to laying out requirements on the construction of the garments, CE
>>>>>> marked and certified products must conform to strict requirements on
>>>>>> the performance of the materials, their colour and the degree of
>>>>>> reflection from the reflective strips.
>>>>>>
>>>>>> Hi-vis jackets and trousers have no ?active? or light-emitting
>>>>>> function, relying instead on an external light source for their
>>>>>> luminescence.
>>>>>> - the fluorescent material: this achieves visibility during the
>>>>>> brighter part of the day but also helps to increase visibility at >>>>>> night
>>>>>>
>>>>>>formatting link>>>>>
>>>>>> In a 2009 literature review, nine papers were found that compared >>>>>> the
>>>>>> visibility of fluorescent and non-fluorescent colours. All but one of
>>>>>> those nine trials found that fluorescent colours were more visible to
>>>>>> drivers. Fluorescent clothing in red, yellow and orange ? colours >>>>>> that
>>>>>> contrast significantly with the riding environment ? was found to be
>>>>>> most effective1.
>>>>>>
>>>>>> During the day, fluorescent clothing takes ultraviolet (UV) light >>>>>> from
>>>>>> the sun ? light we can?t see ? and converts it into light we can see.
>>>>>> The result is an increase in the total amount of visible light that?s
>>>>>> reflected off the clothing, giving fluoro clothing a brighter
>>>>>> appearance. This is particularly the case in low-light conditions,
>>>>>> around dawn and dusk.
>>>>>>
>>>>>>formatting link
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> Bright, synthetic and, above all, cheap, the ubiquity of
>>>>>> high-visibility clothing means that it surely symbolises the Britain
>>>>>> of 2010s in the same way that miniskirts summed up the 1960s. >>>>>>
>>>>>> It was invented by an American, Bob Switzer, whose ambitions of
>>>>>> becoming a doctor ended when he was injured in an industrial accident
>>>>>> during the 1930s. While recuperating, he developed a fluorescent >>>>>> paint
>>>>>> before fashioning the first item of high-visibility clothing from his
>>>>>> wife's wedding dress.
>>>>>>
>>>>>> High-vis first came to the UK in 1964 when it was trialled by railway
>>>>>> maintenance workers in Glasgow.
>>>>>>
>>>>>>formatting link>>>>>
>>>>>> Peter Rhodes, a lecturer in colour at Leeds University, said: ?There
>>>>>> is definitely an element of colour blindness. In safety you are >>>>>> trying
>>>>>> to stand out. Conspicuity is the key element, not brightness per se.
>>>>>> And if everyone wears hi-vis, people tend to ignore you.?
>>>>>>
>>>>>> The biggest market for it now is children. Yoko, a manufacturer and
>>>>>> importer based in Birmingham, says it has made an estimated one
>>>>>> million hi-vis vests for children in the last year alone. Many of
>>>>>> these vests are bought by companies, such as Specsavers and Toyota,
>>>>>> which print their logo on the back and give them to schools, who pass
>>>>>> them on to pupils, who in turn become walking adverts for these
>>>>>> companies. Clever.
>>>>>>
>>>>>>formatting link
>>>>>>
>>>>>>
>>>>>
>>>>> Ah I see, like fluorescent tubes. I didn't realise there was enough
>>>>> natural UV light to make that work, especially in the evening. I >>>>
>>>> Actually in the early evening after sunset the scattered light from the
>>>> blue sky is very UV rich as a proportion of the fading twilight. You >>>> can
>>>> often see things fluorescing an hour or two after sunset at this >>>> time of
>>>> year. If you are lucky you can also see faint electric blue notilucent
>>>> clouds that are so high they remain in sunlight long after sunset. >>>
>>> Then why don't we get a lot more suntan and sunburn in the evening?
>>> Those happen at midday.
>>
>> It is the ratio of diffuse UV and blue light scattered from a clear sky
>> to the low light level of dusk. In direct sunlight there is a lot more
>> UV but there is much more visible light too. When the sun goes down the
>> mid band visible light decreases fastest leaving some reds and UV. >>
>> The intensity is well down but the proportion of UV is much higher. >
> Understood.
Really? Prove it.