On Thu, 29 Aug 2019 01:53:34 +0100, Fredxx wrote:

On 28/08/2019 20:34, Commander Kinsey wrote:
On Wed, 28 Aug 2019 20:18:23 +0100, Martin Brown
wrote:

On 28/08/2019 15:08, Commander Kinsey wrote:
On Wed, 28 Aug 2019 10:30:14 +0100, Martin Brown
wrote:

On 27/08/2019 18:47, Commander Kinsey wrote:
On Tue, 27 Aug 2019 18:36:16 +0100,
wrote:

On Tuesday, 27 August 2019 17:25:45 UTC+1, Commander Kinsey wrote:
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 €œactive€� 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

https://www.healthandsafetyatwork.co...ble-difference

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 cant see €” and converts it into light we can see.
The result is an increase in the total amount of visible light thats
reflected off the clothing, giving fluoro clothing a brighter
appearance. This is particularly the case in low-light conditions,
around dawn and dusk.

https://cyclingtips.com/2016/06/does...make-us-safer/




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.

https://www.bbc.co.uk/news/magazine-14720101

Peter Rhodes, a lecturer in colour at Leeds University, said: €œThere
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.

https://www.telegraph.co.uk/news/hea...ke-lemons.html



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.

What a stupid thing to say.