Re: [magnitude6] glare, cars and illuminated roads

[JohnMurrell <johnmurrell@compuserve...>]

Odd this subject came up today I was talking to a friend about this when I
was walking home an hour ago !

A couple of points come to mind.

First in the UK in before about the mid 1970's it was common for cars to
drive around on their side (parking) lights in lit areas, bearing in mind
that the highway lighting levels were a lot lower then. At that time if you
attempted to drive in lit area with (dipped) headlights people coming the
other way would flash their headlights till you turned them off. This
changed after the government introduced regulations stating that you must
use dipped headlights in poor visibility.

This has resulted in drivers loss of dark adaptation due to the glare from
oncoming headlights. As a result higher lighting levels are being adopted
to get over the fact that the eye is not dark adapted and I suspect that
the pupil contracts due to the glare from the oncoming lights. This is made
worse by modern fittings that to get more control of the light distribution
have smaller more intense light sources that are visible to the driver as
they have still not adopted full cut off lighting in most of the UK. On a
couple of roads near me the glare from the fittings is so bad that the
visibility increases greatly if you drive around with your sun visor
shielding the light fittings !

I have noticed two pieces of evidence that shows the lack of dark
adaptation when driving. The first is that when I drive to our observatory
which involves several miles on lit roads and the last ½ mile or so on
unlit roads it is obvious that when you arrive you are not able to see that
much despite the sky glow from London. After you arrive and your eyes dark
adapt you can see almost as clearly as in daylight ! The  second evidence
is when driving along some of the motorways in the U.K. which are unlit
except at junctions. As you approach the lit junction the lighting is
extremely bright, as you exit into the dark area you realise that you can
see very little despite still having your headlights on.

With regard to oncoming headlights there was a suggestion a long while ago
that lights should be vertically polarised and drivers should wear glasses
with horizontally polarized lenses so that the glare would be minimised but
you could still see things illuminated by the headlights as the object
would rotate the light polarisation. 

I believe that the other factor that has effected glare is that drivers
expect to 'Jump into their Cars' and go even at night when emerging from a
bright building. If one looks back buildings were not lit to the same
standard and people spend more time cleaning the windows of their car /
defrosting them, in the prevailing levels of street lighting this allowed
the eyes to become partially adapted.

Does anyone know of any research into the dark adaptation of drivers eyes
and the effect of glare both on dark adaptation and the size of the pupil ?

John Murrell
Croydon Astronomical Society U.K.

Message text written by INTERNET:magnitude6@yahoogroups...
> 
j.ipa@wanadoo... wrote:

<< ...  Car's lights are much powerful nowadays and while driving through
 illuminated  roads or streets this is not a problem; but when you face
them
 in non-illuminated roads they really disturb and produce glare ..... >>

Jordi,
        In the USA, the national traffic safety board has received hundreds

of letters complaining about new headlights.  They have been studying this 
issue for several years, and I don't know the latest.

Cheers from Italy, 
             Bob Gent
             European Liaison Officer 
             International Dark-Sky Association
                        www.darksky.org <


------------------------ Yahoo! Groups Sponsor ---------------------~-->
Get your FREE credit report with a FREE CreditCheck
Monitoring Service trial
http://us.click.yahoo.com/ACHqaB/bQ8CAA/ySSFAA/Kv0qlB/TM
---------------------------------------------------------------------~->

http://www.egroups.com/group/magnitude6 
Posting address: magnitude6@egroups... 
To unsubscribe from this group, send an email to:
magnitude6-unsubscribe@egroups...
 

Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/