The Naked Scientists

The Naked Scientists Forum

Author Topic: What's The Haze Surrounding Street Lighting ?  (Read 7393 times)

Offline neilep

  • Withdrawnmist
  • Naked Science Forum GOD!
  • *******
  • Posts: 20602
  • Thanked: 8 times
    • View Profile
What's The Haze Surrounding Street Lighting ?
« on: 20/09/2012 11:32:34 »
Dearest Streetlightologists,

As a sheepy I of course luff street lights. Lets face it...what is more exciting than to pass by a street light on a night out or perchance just to stand beside one ?...well, I can't think of anything more I'd rather do, and I just know ewe agree !

Take a look at the street lights below.





A piccy of the streetlights that I mentioned in the above sentence.


Nice eh ?...as far as street lights go these are real lookers !



Notice how non focused the actual illumination is though ?...it's a bit fuzzy ?...why's that then ?...is it my eyes ?...then how come it appears in the photo ?..or is it some kind of magical fairy street light dusty stuff ?


Ewe see.....I don't know.....I'd like to know...what is the haze surrounding street lighting ?



Hugs and shmishes


mwah mwah



Neil
A heavy light is not an oxymoron
xxxxxxxxxxxxxxxxxxxxxxxxxxxx





« Last Edit: 20/09/2012 11:53:43 by neilep »


 

Offline RD

  • Neilep Level Member
  • ******
  • Posts: 8126
  • Thanked: 53 times
    • View Profile
Re: What's The Haze Surrounding Street Lighting ?
« Reply #1 on: 21/09/2012 16:55:38 »
The "haze" is in the eye of the beholder : a diffraction effect caused by the pupil, ( or camera aperture * ).

The wikipedia examples below use monochromatic laser light rather than white light so include concentric features which the white street lamps wouldn't have ...

https://en.wikipedia.org/wiki/File:Diffraction_on_elliptic_aperture_with_fft.png

https://en.wikipedia.org/wiki/File:Laser_Interference.JPG

[ * the photo versions can be a starburst with six or eight rays due to the number of blades in the lens variable aperture  ]
« Last Edit: 21/09/2012 17:07:26 by RD »
 

Offline neilep

  • Withdrawnmist
  • Naked Science Forum GOD!
  • *******
  • Posts: 20602
  • Thanked: 8 times
    • View Profile
Re: What's The Haze Surrounding Street Lighting ?
« Reply #2 on: 21/09/2012 17:31:57 »
The "haze" is in the eye of the beholder : a diffraction effect caused by the pupil, ( or camera aperture * ).

The wikipedia examples below use monochromatic laser light rather than white light so include concentric features which the white street lamps wouldn't have ...

https://en.wikipedia.org/wiki/File:Diffraction_on_elliptic_aperture_with_fft.png

https://en.wikipedia.org/wiki/File:Laser_Interference.JPG

[ * the photo versions can be a starburst with six or eight rays due to the number of blades in the lens variable aperture  ]

Thanks RD...so ..the diffraction is not really there....it's an illusion caused by our own ocular implants eh ?....So....what's affecting my pupils to cause such diffraction  ?

 

Offline JP

  • Neilep Level Member
  • ******
  • Posts: 3366
  • Thanked: 2 times
    • View Profile
Re: What's The Haze Surrounding Street Lighting ?
« Reply #3 on: 21/09/2012 18:18:13 »
Very roughly, diffraction is the tendency of light to bend around edges.  Cameras have apertures which limit the light coming into them, and eyes have pupils to do the same job.  There are a lot of ways to model this, but one particularly simple model is that whenever light hits an obstacle, it tends to scatter primarily in the direction perpendicular to that edge.  That's why in the images you posted, as RD mentioned, you can see a bunch of streaks coming radially out of image of the lamp. 

Even if you had perfect lenses (which you never do), the size/shape of your aperture would place fundamental limits on your image resolution and quality just due to diffraction.
 

Offline neilep

  • Withdrawnmist
  • Naked Science Forum GOD!
  • *******
  • Posts: 20602
  • Thanked: 8 times
    • View Profile
Re: What's The Haze Surrounding Street Lighting ?
« Reply #4 on: 22/09/2012 05:47:36 »
Very roughly, diffraction is the tendency of light to bend around edges.  Cameras have apertures which limit the light coming into them, and eyes have pupils to do the same job.  There are a lot of ways to model this, but one particularly simple model is that whenever light hits an obstacle, it tends to scatter primarily in the direction perpendicular to that edge.  That's why in the images you posted, as RD mentioned, you can see a bunch of streaks coming radially out of image of the lamp. 

Even if you had perfect lenses (which you never do), the size/shape of your aperture would place fundamental limits on your image resolution and quality just due to diffraction.

JP..Thank You.
 

Offline chris

  • Neilep Level Member
  • ******
  • Posts: 5336
  • Thanked: 65 times
  • The Naked Scientist
    • View Profile
    • The Naked Scientists
Re: What's The Haze Surrounding Street Lighting ?
« Reply #5 on: 22/09/2012 20:13:25 »
What is the mechanism behind diffraction of light, sound, water waves etc?
 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8660
  • Thanked: 42 times
    • View Profile
Re: What's The Haze Surrounding Street Lighting ?
« Reply #6 on: 22/09/2012 22:00:05 »
How sure are you that the blur round the lights is not due to scattering?
Here's a nice picture of some street lights in fog (so there are lots of scattering centres) and the effect is more pronounced.
http://jaumf.deviantart.com/art/Foggy-Lights-74335410
 

Offline evan_au

  • Neilep Level Member
  • ******
  • Posts: 4116
  • Thanked: 245 times
    • View Profile
Re: What's The Haze Surrounding Street Lighting ?
« Reply #7 on: 23/09/2012 04:32:40 »
The "haze" effect is accentuated due to over-exposure.

The original photograph exposure is optimised to show the green grass (so much loved by sheep), and the black road. However, these reflect only a very small fraction of the light falling on them - the intensity of the street lights is thousands of times higher.

If you took the same photo, but optimised the exposure for the street lights, the grass would be black (and the road even blacker), but the haze around the street lights would be much reduced.

There would still be a bit of haze due to the effects mentioned above - dust in the atmosphere, diffraction at the camera iris, partial reflections inside the camera lens elements, smudges on the lens, etc.
 

Offline RD

  • Neilep Level Member
  • ******
  • Posts: 8126
  • Thanked: 53 times
    • View Profile
Re: What's The Haze Surrounding Street Lighting ?
« Reply #8 on: 23/09/2012 08:34:52 »
How sure are you that the blur round the lights is not due to scattering?
Here's a nice picture of some street lights in fog (so there are lots of scattering centres) and the effect is more pronounced.
http://jaumf.deviantart.com/art/Foggy-Lights-74335410

The visibility on Neilep's street-lamp photo is at least three hundred fog-free meters, ( I counted the lamp-posts ).

Below is an example of the effect of the camera aperture size on producing the starburst (diffraction) effect ...


http://www.cameratechnica.com/2011/02/24/how-to-create-and-avoid-starburst-highlights/
« Last Edit: 23/09/2012 08:57:20 by RD »
 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8660
  • Thanked: 42 times
    • View Profile
Re: What's The Haze Surrounding Street Lighting ?
« Reply #9 on: 23/09/2012 10:32:06 »
I didn't say it was foggy in Neil's picture.
I did show that scattering gives rise to a similar looking halo where there's a lot of stuff in the air to scatter light.
As Evan has pointed out, the over exposure emphasises it.
The pics of the Christmas tree lights show a nice clear six  pointed star due to diffraction at the iris.
The OP doesn't.
My guess is it's a combination of effects, not least a smudge on the lens.
 

The Naked Scientists Forum

Re: What's The Haze Surrounding Street Lighting ?
« Reply #9 on: 23/09/2012 10:32:06 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums