I'll have to render some _dark_ scenes and then check them out after adapting to
the dark...

http://www.laserfocusworld.com/articles/print/volume-52/issue-01/features/photonic-frontiers-color-measurement-light-so
urces-and-vision-led-lighting-makes-new-demands-on-color-measurement.html


"In mesopic vision, eye response varies from the photopic extreme of fully
light-adapted (m=1) to the scotopic extreme when fully dark-adapted (m=0). Note
that the eye is far more sensitive to blue light in the dark, making blue light
look brighter at low light levels. (Courtesy of Teresa Goodman, National
Physical Laboratory, UK)"

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On 01/25/2017 04:05 PM, Bald Eagle wrote:
> "In mesopic vision, eye response varies from the photopic extreme of fully
> light-adapted (m=1) to the scotopic extreme when fully dark-adapted (m=0). Note
> that the eye is far more sensitive to blue light in the dark, making blue light
> look brighter at low light levels. (Courtesy of Teresa Goodman, National
> Physical Laboratory, UK)"

And if our eyes are more sensitive to blue light when dark-adapted, it 
must be a marvelous idea to install blue filters over car headlights, 
right?  Hence, how so many motorists with a naive understanding of how 
human vision works are conned into an illegal modification to their 
headlights that kills my night vision while simultaneously making their 
headlights *less* effective.

(If the people who are blithely unaware of the existence of their dimmer 
switch weren't bad enough.)

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On 01/29/2017 07:35 AM, Cousin Ricky wrote:
> On 01/25/2017 04:05 PM, Bald Eagle wrote:
>> "In mesopic vision, eye response varies from the photopic extreme of
>> fully
>> light-adapted (m=1) to the scotopic extreme when fully dark-adapted
>> (m=0). Note
>> that the eye is far more sensitive to blue light in the dark, making
>> blue light
>> look brighter at low light levels. (Courtesy of Teresa Goodman, National
>> Physical Laboratory, UK)"
>
> And if our eyes are more sensitive to blue light when dark-adapted, it
> must be a marvelous idea to install blue filters over car headlights,
> right?  Hence, how so many motorists with a naive understanding of how
> human vision works are conned into an illegal modification to their
> headlights that kills my night vision while simultaneously making their
> headlights *less* effective.
>
> (If the people who are blithely unaware of the existence of their dimmer
> switch weren't bad enough.)

P.S.  The "bluish" 4000 K whites referred to in the article are redder 
than daylight, and far, far redder than the blue headlight 
modifications.  I estimate the daylight CFLs in my bedroom to be around 
4150 K to 4230 K (they are glaringly more bluish than the lights 
emanating from other homes), but they are noticeably more yellowish than 
the white of my computer monitor.

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> I'll have to render some _dark_ scenes and then check them out after adapting to
> the dark...
>
>
http://www.laserfocusworld.com/articles/print/volume-52/issue-01/features/photonic-frontiers-color-measurement-light-so
> urces-and-vision-led-lighting-makes-new-demands-on-color-measurement.html
>
>
> "In mesopic vision, eye response varies from the photopic extreme of fully
> light-adapted (m=1) to the scotopic extreme when fully dark-adapted (m=0). Note
> that the eye is far more sensitive to blue light in the dark, making blue light
> look brighter at low light levels. (Courtesy of Teresa Goodman, National
> Physical Laboratory, UK)"
>
>

This look strange. Blue light cause your iris to contract, reducing the 
amount of light that enter the eye. It also cause saturation of the sick 
cells in your retina, killing night vision. At the same time, the eye is 
far more censible to light in the yellow region whitch don't cause 
saturation nor contraction of the iris.
When sodium lighting was adopted, the considerations where:
It pierce fog and smoke.
It preserve night vision.
It takes less lumens to get the same physiological brightness.
The lumen to wat ratio is higher.

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Am 29.01.2017 um 15:13 schrieb Alain:

>> I'll have to render some _dark_ scenes and then check them out after
>> adapting to
>> the dark...
>>
>>
http://www.laserfocusworld.com/articles/print/volume-52/issue-01/features/photonic-frontiers-color-measurement-light-so
>>
>> urces-and-vision-led-lighting-makes-new-demands-on-color-measurement.html
>>
>>
>> "In mesopic vision, eye response varies from the photopic extreme of
>> fully
>> light-adapted (m=1) to the scotopic extreme when fully dark-adapted
>> (m=0). Note
>> that the eye is far more sensitive to blue light in the dark, making
>> blue light
>> look brighter at low light levels. (Courtesy of Teresa Goodman, National
>> Physical Laboratory, UK)"
>>
>>
> 
> This look strange. Blue light cause your iris to contract, reducing the
> amount of light that enter the eye. It also cause saturation of the sick
> cells in your retina, killing night vision. At the same time, the eye is
> far more censible to light in the yellow region whitch don't cause
> saturation nor contraction of the iris.
> When sodium lighting was adopted, the considerations where:
> It pierce fog and smoke.
> It preserve night vision.
> It takes less lumens to get the same physiological brightness.
> The lumen to wat ratio is higher.

... and they _may_ have been wrong in their assessments back then.
Science advances as people make more and more experiments and field
studies, and do so in an increasingly controlled manner.

Also note that the article does not conclude with "We should make LED
street lamps less bright", but "We have more to learn about the impact
of LED lighting on color measurement, standards, and illumination."


Besides, are you sure the 3rd and 4th criteria on your list actually
reflect the considerations back then? I'd have expected them to be
collapsed into just a single criterion:

    "It takes less Watts to get the same physiological brightness."

That is, unless legislation about the brightness of street lights had
already been in place then -- because there is no other reason to worry
about the lumens -- in which case my guess would be that the 3rd
criterion wasn't considered at all, just the 4th criterion.


And last not least, road illumination should (well, _must_) consider
interaction with other important sources of illumination present on dusk
and night roads, most notably car headlights. Back when sodium lamps
were introduced, tungsten incandescent bulbs were the prevalent means
for cars to carry their own light source, but there is a long-standing
trend towadards xenon lamps (and also those idiotic "fake xenon"
blue-filter tungsten lamps), which have a significantly higher
temperature, and I guess there's also the occasional LED headlight out
there by now (not to be confused with the already common white LED
"position lights" intended for daylight use).


(Besides the issue of visibility, "blue" street lights would also have a
slight advantage in keeping drivers awake at night. And a corresponding
disadvantage in also more strongly influencing the day-night rhythm of
local residents, both human and animal.)

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Am 29.01.2017 um 15:13 schrieb Alain:

>> "In mesopic vision, eye response varies from the photopic extreme of
>> fully
>> light-adapted (m=1) to the scotopic extreme when fully dark-adapted
>> (m=0). Note
>> that the eye is far more sensitive to blue light in the dark, making
>> blue light
>> look brighter at low light levels. (Courtesy of Teresa Goodman, National
>> Physical Laboratory, UK)"
> 
> This look strange. Blue light cause your iris to contract, reducing the
> amount of light that enter the eye. It also cause saturation of the sick
> cells in your retina, killing night vision. At the same time, the eye is
> far more censible to light in the yellow region whitch don't cause
> saturation nor contraction of the iris.

BTW, this is exactly the point the article is raising: The eye is _not_
universally most sensitive to yellow light. Instead, the wavelength of
highest sensitivity depends on the total brightness, with the
sensitivity of daylight vision peaking at yellow, night vision peaking
at a blue-green ("blue-ish") hue, and "mixed" vision (which appears to
be the case applicable for night-time traffic) peaking somewhere in between.

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Yes, I thought the 'take-home' message was along the lines of "what you see
depends strongly upon not only the lighting, but how your eye has _adapted_ to
that lighting"


The story I was told about yellow street lamps was that it didn't cast harsh
shadows with a high contrast, and so they were better for public safety since it
gave a better overall illumination.

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