Foreground light, pupil constriction, color temp and color spectrum.

[-Virgil-]

I will know for sure after Christmas when my spectrometer comes in .... cool new toy! Damn excited! I have some free time after Christmas so there may even be a home brew goniospectrophotometer in my future.

Cool!

There's an awful lot of what we might call "post-processing" going on in the visual system to clean up the noisy image on the retina, and it seems blue light requires the most such post-processing. Reading your observations on blue-white vs. orange-white street lighting, I find myself reminded not only of your earlier remarks regarding the relatively strong pupillary constriction response to relatively bluer light vs. relatively yellower light, but also of certain aspects of the studies linking bluer headlight spectra to increased glare perception without concommitant increased visual acuity. I think your observation is probably covered by some mix of these effects, and I think you are perceiving the primacy of reduced light reaching the retina (which tends to reduce distance visual acuity) over depth-of-focus effects (which tend to increase distance visual acuity). Another potential contributing factor could be the photometrics of the LED vs. HPS street lights. The next neighborhood over from mine has been getting LED replacements for its HPS lamps, but the pole spacing and count are not changing. The gradients are much more prominent on the road surface, i.e., the LED heads produce a smaller circle of light and the effect is of alternating bright and dark zones that weren't nearly as prominent with the HPS lamps. I haven't quite fully mulled over how this might tend to contribute to the effect you noticed, but it seems to me it might.

 

[TEEJ]

Interesting material.

I also think that generally, trying to focus on distal targets which involve the fovea means you are primarily using the central rods in that ~ 2º cone of vision....which are worse in low light/need more light to discern details, etc. Add the frequency related aspects of the melanopsin expressing ganglion cells, which could be triggered as well, and it could explain a lot of what has been expressed in terms of studies and anecdotes.

 

[SemiMan]

Cool!

There's an awful lot of what we might call "post-processing" going on in the visual system to clean up the noisy image on the retina, and it seems blue light requires the most such post-processing. Reading your observations on blue-white vs. orange-white street lighting, I find myself reminded not only of your earlier remarks regarding the relatively strong pupillary constriction response to relatively bluer light vs. relatively yellower light, but also of certain aspects of the studies linking bluer headlight spectra to increased glare perception without concommitant increased visual acuity. I think your observation is probably covered by some mix of these effects, and I think you are perceiving the primacy of reduced light reaching the retina (which tends to reduce distance visual acuity) over depth-of-focus effects (which tend to increase distance visual acuity). Another potential contributing factor could be the photometrics of the LED vs. HPS street lights. The next neighborhood over from mine has been getting LED replacements for its HPS lamps, but the pole spacing and count are not changing. The gradients are much more prominent on the road surface, i.e., the LED heads produce a smaller circle of light and the effect is of alternating bright and dark zones that weren't nearly as prominent with the HPS lamps. I haven't quite fully mulled over how this might tend to contribute to the effect you noticed, but it seems to me it might.

While the pole spacing is the same as the HPS lighting, it is a quality installation in that the uniformity is quite good. Visually I would say the uniformity is superior to the HPS lighting not that the HPS lighting was that bad.

I should also clarify that the HPS lighting is the older style drop glass lens types, not one of the newer full cutoff fixtures. The LED fixtures were the "traditional" flat array of LEDs and lenses style. The side of the array was not shielded to prevent light above 70 degrees, though I believe these are RUUD or Lighting Science and I think they are full cutoff as well so they will limit light beyond 70 degrees.

We are getting outside "automotive" here, but I think the discussion is more warranted here for the technical aspects as it applies to roads and automotive.

 

[degarb]

While the pole spacing is the same as the HPS lighting, it is a quality installation in that the uniformity is quite good. Visually I would say the uniformity is superior to the HPS lighting not that the HPS lighting was that bad.

I must say, SemiMan, you really know how to get to the heart of an argument. I like your ability to condense information to a practical conclusion that we can use. (I would like to see a paper/webpage with exclusively your long range conclusions and distillations.)

I am bookmarking thread, along with http://www.candlepowerforums.com/vb...or-flood-than-for-throw&p=4114657#post4114657 eh4 had a good distillation.

 

[intessol]

Re: glare/painful or disabling glare - since vision is not just the optical system, but heavy on the image-processing in the visual cortex, it may be that the poorly focused light of glare (shorter wavelengths not as well focused) is overwhelming the processing which attempts to bring the imperfect retinal image into a clearly-mapped focus on the visual cortex. This in turn sends an error message that says "You're swamping me! Turn away!" In saying this, I have told you more than I know about vision, except for one anecdotal reference: I sat at my telescope for the first time and pointed it at what should have been Saturn. All I saw was a blob. Everything else (stars (point sources)) was in focus. It was a blob. But suddenly, as I persisted in looking at it, RINGS APPEARED! And the shadow of the planet cast itself across the rings as they turned past the planet! My visual cortex had processed the confused mess I sent it, and showed me Saturn in all its glory! I formed there a rich kinship with the first astronomers, who saw and documented things that no one else saw for decades or centuries, until technology advanced to make it obvious. It is still (30 years) a God-the-Magnificent-Creator moment to me.

I am led by such insights to believe that the search for the optimal headlight SPD is very important. The current collection of blue-turning-to-yellow-on-approach from heavily lensed bulbs, hot blue to white from others, compared to the various yellows of older vehicles, many with electrical issues causing less-than-optimal voltage to headlamps, is irritating, and probably dangerous to some extent.

 

[SemiMan]

... then again it could have just been focus creep on your telescope

The correct answer is likely not just one SPD, but perhaps multiple SPDs. There is a strong argument that within the primary visual cone, 2 degrees, that there is little benefit to high CCT, but all the negativity if that light spreads outwards and creates glare, especially with the high intensities desired for long range illumination. Sure, you will want to keep it wider than 2 degrees as we do move our head. When you are looking at illuminating the side of the road, though, higher CCT at lower intensity would be useful.

 

[lumen aeternum]

So 3 years from the OP, what's the state of car headlamps? If you are buying a car & have options, what to choose?

For experimenting with blue wrt glare -- you could get a blue LED keychain light and clip it to the visor and shine it at your face. Might want to be the passenger.

 

[-Virgil-]

So 3 years from the OP, what's the state of car headlamps?

The state of the art keeps advancing. More and more cars come with LED headlamps as standard or optional equipment. Halogen headlamps are still predominant. HID headlamps are slowly going away.

If you are buying a car & have options, what to choose?

Depends on what car and what options!

For experimenting with blue wrt glare -- you could get a blue LED keychain light and clip it to the visor and shine it at your face. Might want to be the passenger.

I assume you're referring to that nutball idea that blue light directed at (or across, or above, or below) the driver's face somehow magically reduced glare from headlamps and such. It's been roundly debunked.

 

[KXA]

They way I get around all of this obsession with high CCT headlights is with selective yellow glasses. They reduce glare for me, but that's my subjective impression.