# LED vs Xenon



## Chimera (Jul 6, 2002)

I'm trying to figure out whether I want to add the LED headlight option. Most of what I've seen online indicates there no gain in nighttime visibility with the LEDs, just a less fatiguing light that's easier on the eyes. Are the LEDs adaptive, turning into corners like the adaptive xenons do or is it not necessary due to the light pattern of the LEDs? Anyone know how many LEDs are in the cluster.. is it 4?


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## steve111b (Jun 2, 2011)

Chimera said:


> light that's easier on the eyes.


This will depend on the driver. LEDs are more intense, which means your pupils will become smaller. Smaller pupils work better and they won't need to adjust as much for oncoming traffic. But there is a trade off. Outside of the light generated by the LEDs you will see less well, which may be unfamiliar and unsettling to some drivers.

LEDs on the A3 are different than those sold in the ROW to comply with conservative lighting rules that exist in North America. I believe that the LEDs in the UK can illuminate side roads as you drive by based on information from the NAV.

A lot depends on your age. Teens have trouble adjusting to oncoming lights (I did). In your 20s and 30s your eyes are flexible enough to adapt to a new style of lighting. After 40 people can struggle with eyesight and one area that becomes difficult is night vision. So if you are over 40 it may take time to adapt to LEDs or you may not wish to subject your eyes to one more stressfull situation.

So there will be a lot of different answers to your questions. My guess is that not a lot of people will shell out the money for LEDs. Some drivers who opt for LEDs may not adapt easily (especially those over 40) to the new technology. All this is theory because I have never tried them.


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## zoolanderer (Apr 16, 2014)

Hey guys,

I'm a member of the VW forum but occassionally stray over here to see what's going on in the Audi world. I just wanted to respectfully disagree with what Steve had said. I am an optometrist and while some points he made may be correct others are actually backwards and I didn't want people to be misinformed on the subject.

First, as the driver sits behind the source of the light (headlights) and they shine away from the driver, there is no stimulus for pupillary constriction regardless of whether it is an LED or xenon light. Sure some light may be reflected back at the driver but the amount is minimal and not enough to constrict the pupils in an otherwise dark environment. It's true that a smaller pupil would have a greater depth of focus/depth of field if indeed the pupils were constricted (but again, at night time without direct illumination they would not be, nor would it be a good thing for them to be.)

The other part of the post about age and adjusting to lighting conditions is also a little backwards. Its true that younger drivers (late teens, early twenties) will stuggle with night driving, but this is because physiologically they have a larger pupil size for a given lighting environment compared to an older driver. This larger pupil allows more off-axis light into the eye and induces something called spherical abberation (and coma for light coming from an oblique angle) which induces blur on the retina, and causes visual phenomenon such as haloes around lights. Pupil size starts to shrink in your twenties, which starts to reduce this issue. As a driver reaches his or her 40s or 50s, night vision again begins to suffer for two reasons. First, pupil size becomes smaller again, and the pupillary constrictor muscle of the iris becomes slower to react to a given stimulus, limiting the amount of light that can enter the eye, and the speed at which it can adjust. While depth of field is increased, illuminace of the retina is decreased, especially peripherally. The peripheral retina is home to mostly rod cells which are responsible for sensing light/dark, motion, contrast amongst other things. The second thing that happens is the crystalline lens starts to yellow and become cloudy by about age 50, which we call a cataract. A cataract scatters light from a point source (oncoming headlight) and again reduces illuminance of the retina as blue light is filtered out by the yellow lens.

No hard feelings, just wanted to clarify some of those things in my understanding of physiological optics. Sorry if my post doesn't address your original question too well, OP.


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## ChrisFu (Jun 9, 2012)

Strange, in a lot of published data regarding headlamp design, strong foreground illumination has been mentioned as a contributor to pupil contraction/dark level adaptation. I believe its often termed "disability glare" as well.




> Approximately 64.5% of drivers in cars with fog lamps use their fog lamps at night in clear-weather conditions not warranting fog lamp use. Fewer drivers (60.6%) use their fog lamps in moderate-to-heavy fog conditions warranting fog lamp use. This indicates that drivers tend to use fog lamps to supplement their low beam headlamps, rather than as an aid to poor-weather visibility. (Sivak et al. 1997). Assuming the lamps in question at least approach the general character of a fog beam, providing primarily foreground illumination and lateral spread, the indication is that drivers want more and wider foreground illumination. They get it by using fog lamps. US low beams have traditionally had less and narrower foreground illumination than comparable ECE low beams primarily due to concern that excessive foreground illumination will limit distance vision by drawing the driver’s visual attention to the foreground or by reducing the driver’s level of dark adaptation. This may not be the case. Olson and Sivak (1983) studied driver eye movements at night as a function of foreground illumination. At high levels of foreground illumination, drivers tended to look further down the road. Olson & Sivak’s interpretation is that with high levels of foreground illumination, drivers tend to use peripheral vision for the foreground and foveal vision for distant points. This may be why drivers prefer higher levels of foreground illumination than is traditionally provided by US low beams.


Much of the debate centers on foreground illumination wavelength, and physiological response to "bluer" versus white or more yellow colour temperatures, and hence OEM's never using HID bulbs in fog lamps. It is also related to the original research that showed the physiological effects which drove all headlamps in France for much of the 20th century as being mandated yellow.


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## zoolanderer (Apr 16, 2014)

Thanks for your response, ChrisFU. I typed a big long response with a few citations but my login timed out before I sent it and I lost it

Basically what I wanted to say was this:

I think that it may not be the high foreground illumination that causes pupillary constriction. Rather, throughout the process of dark adaptation the "gain" of the system is reduced, so what once took 1000 photons to make a cell "see" only takes 10. Complex feedback loops within the retina and throughout the brain then adjust things like pupillary size accordingly to maintain a steady state.

I wouldn't think that one's own headlight would cause disability glare, per se, because this type of glare is dependant upon the amount light incident upon the retina (illuminance) rather than projected into the environment (luminance). Thoughts?

There was one line in that quote that I feel was an incorrect hypothesis by the authors, at least partially.
"At high levels of foreground illumination, drivers tended to look further down the road. Olson & Sivak’s interpretation is that with high levels of foreground illumination, drivers tend to use peripheral vision for the foreground and foveal vision for distant points"
I don't get why drivers would choose to use peripheral vision for foreground vision if the majority of the peripheral retina is made up of rod cells, which function better in low light conditions. Additionally, I feel like the comment about foveal vision is confounded because humans use foveal vision for distance tasks automatically because it is the only part of the retina capable of useful visual resolution in the distance. Even about 5 degrees eccentric to the fovea, acuity drops from 20/20 to the 20/100-200 level.

Thanks again for taking the time to respond and educate me. Any other thoughts?


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## ChrisFu (Jun 9, 2012)

Well I am an aerospace engineer by trade, but an automotive lighting "hobbyist" so my knowledge is far limited to just reading the studies and perusing thoughts of many others (particularly Daniel Stern over the years).

I agree entirely with your sentiments, though, and am amazed we (or more accurately, scientists in the field) have been able to distill some objective data from what is a very inherently subjective phenomenon!

Candlepower is the place to check out if you want to get in the weeds of the matter, I go over there to geek out on the subject from time to time.


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## zoolanderer (Apr 16, 2014)

Thanks! I'll check it out. Always curious to learn more.


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## Lpforte (Aug 2, 2011)

That blurb makes it sound like US spec low beams are purposely narrow because of the _possibility_ of reduced low light adaptation, not because of a proven reduction. There is a distinct difference. A LOT of federal safety regulations for vehicles are based on technology and scientific knowledge from half a century ago. 

Another thing to note: due to the positioning and angle of fog lights, they produce much more intense reflections back towards the driver than typical low beams. I believe this is why it is considered dangerous to use them in conditions that don't warrant it (basically anything less than severe weather which requires you to slowly follow road markings just a dozen feet or so in front of you). The scattered light is both a distraction for oncoming drivers, and the driver using the lights has reduced sensitivity to objects down the road because the area immediately in front of your vehicle is flooded with light.


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## iceorbital (Jul 2, 2011)

On a somewhat related note, are the standard xenon adaptative on the us a3 sedan?


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## caliatenza (Dec 10, 2006)

ChrisFu said:


> Strange, in a lot of published data regarding headlamp design, strong foreground illumination has been mentioned as a contributor to pupil contraction/dark level adaptation. I believe its often termed "disability glare" as well.
> 
> 
> 
> ...


i had to use the fog lights to supplement the halogen lighting on my dad's new F30 when i went out of town recently; the halogens that BMW puts on their cars aren't great...my eyes had trouble adjusting to them. The fog lights helped, but not much.


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## steve111b (Jun 2, 2011)

Welcome to the Audi side zoolanderer. Hope you enjoy your stay here. I have no problem with your comments concerning my views about eyes and LEDs. Always nice to hear other people's opinions.

I would like to add that I never claimed to be an expert and I ended with "all this is theory". Those people who read my words can decide if they have any merit. I recently read an article in the newspaper about LED lights (google LED lighting Ottawa). I have an interest in this new technology. For 15 years I have been following natural vision improvement and have managed to avoid wearing glasses. I would be happy to hear anything anyone has to say about how LED headlights work.


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## mlin32 (Aug 15, 2013)

Like someone mentioned, the real benefit of the LED headlamps is their matrix headlamp ability, where LEDs can selectively illuminate portions and areas adaptively. This is legal and possible outside the US. Essentially, one can leave the headlights on full/high beam all the time without blinding traffic because the camera sensor will detect vehicles ahead and oncoming and change the light matrix so the light beam is thrown to the side or dipped, and this can occur on one side/headlight of the vehicle. A search on Youtube will be better than me trying to explain.

I don't know if anyone has tried coding with the VAG-COM on this feature. Someone in the US has already decoded the US/Canadian restriction on their BMW F15 LED headlights that enable the smart functionality described above.


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## Dan Halen (May 16, 2002)

I'm more concerned about enabling the gradient turn signals.


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## WLV (Apr 23, 2014)

I spoke to the head of Audi lighting about this when they first showed it at the Consumer Electronics Show 18 months ago. As he related to me, the US DOT "only understands low beams and high beams." They can't wrap their heads around the idea of a continually changing lighting pattern based on road conditions.

When I asked him about it again a year ago, he said he thought they were no closer to getting DOT approval.

Also, regarding sequential turn signals, the reason Audi can't get DOT approval while Ford can do the same thing on the Mustang is because each individual turn signal LED on the Audi is smaller than required by US rules. Ford's individual LED panels are much larger.

And while we're on the subject, if you've wondered why the DRLs go off in the daytime when the front turn signals go on, blame the DOT, not Audi. Again, there's a rule that says if a DRL is of a certain brightness it must go off so that the turn signal can be seen. I believe this can be altered with the VAG-COM.


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## caliatenza (Dec 10, 2006)

WLV said:


> I spoke to the head of Audi lighting about this when they first showed it at the Consumer Electronics Show 18 months ago. As he related to me, the US DOT "only understands low beams and high beams." They can't wrap their heads around the idea of a continually changing lighting pattern based on road conditions.
> 
> When I asked him about it again a year ago, he said he thought they were no closer to getting DOT approval.
> 
> ...


stupid DOT; but i guess only if a domestic automaker lobbies them, things would change.


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## Dan Halen (May 16, 2002)

Correct on the VagCom statement. :thumbup:

Sent from my Nexus 5 using Tapatalk


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