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Design Rationale for DRL Behavior

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Old 07-15-17, 11:34 PM   #1
xfumbler
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Default Design Rationale for DRL Behavior

What is the design rationale wherein either left or right daytime headlights will turn off when the corresponding turn indicator is turned on? I've noticed this behavior a few times in newer car models, specifically Audis.
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Old 07-15-17, 11:57 PM   #2
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The rational is that the bright white DRL could detract from the visibility of the turn signal, thus making it potentially dangerous for oncoming traffic. However, it varies per automaker.

Last edited by RXSF; 07-16-17 at 12:03 AM.
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Old 07-15-17, 11:58 PM   #3
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Originally Posted by xfumbler View Post
What is the design rationale wherein either left or right daytime headlights will turn off when the corresponding turn indicator is turned on? I've noticed this behavior a few times in newer car models, specifically Audis.
It's because they use the same lamps in some cases, so they don't want the DRL illumination to distract from the turn signal, it makes the turn signal "stand out" more. It's a safety thing, supposedly.

-Mike
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Old 07-16-17, 12:21 AM   #4
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Huh, I thought it was for looks or just to be different. I can't imagine I wouldn't notice a turn signal because of the DRL's.

Thanks for the fast response.
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Old 07-16-17, 12:49 AM   #5
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Audi, Ford, Jaguar, so far. What's distracting is that they seem to use the same array for DRLs and indicators so the switchover is distracting. Dynamic KITT indicators make things even worse. I prefer having DRLs and indicators separated.

Last edited by chromedome; 07-16-17 at 12:53 AM.
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Old 07-16-17, 04:22 AM   #6
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Drgrant is correct. It's generally a shared-light issue. Some states have laws saying that headlights or DRLs must be on when using wipers in bad weather or visibility is less than 500 feet. This set-up (apparently) satisfies those laws, even though only one headlight/DRL is on when the turn-signals are blinking. At least I haven't heard of anyone getting a ticket (yet) for that.
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Old 07-16-17, 06:54 AM   #7
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I thought someone says there was a reg that if the drl is within x " or cm of the turn signal it had to do that, but my BMW as an '07 has cornering lamps which would actually do the opposite, light up even brighter when the turn signals are on (actually they operate indendently but we're assuming one signals when turning)....
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Old 07-16-17, 07:44 AM   #8
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Quote:
Originally Posted by mmarshall
Drgrant is correct. It's generally a shared-light issue. Some states have laws saying that headlights or DRLs must be on when using wipers in bad weather or visibility is less than 500 feet. This set-up (apparently) satisfies those laws, even though only one headlight/DRL is on when the turn-signals are blinking. At least I haven't heard of anyone getting a ticket (yet) for that.
DRLs do NOT satisfy the requirement for headlights to be on in the rain.

The point really is rear marker lamps. Rear lamps don't illuminate with the DRLs.

When they say "headlights need to be on", they mean headlights.

http://www.santacruzlive.com/streets...lights-on-law/

http://www.city-data.com/forum/new-j...ticket-if.html
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Old 07-16-17, 08:22 AM   #9
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Quote:
Originally Posted by chromedome View Post
Audi, Ford, Jaguar, so far. What's distracting is that they seem to use the same array for DRLs and indicators so the switchover is distracting. Dynamic KITT indicators make things even worse. I prefer having DRLs and indicators separated.
I tend to agree but I love how Mercedes has the DRL fade back on instead of the abrupt switch back
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Old 07-16-17, 10:07 AM   #10
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Quote:
Originally Posted by RXSF
I tend to agree but I love how Mercedes has the DRL fade back on instead of the abrupt switch back
The DRLs fading is a very nice touch.
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Old 07-16-17, 10:08 AM   #11
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Well, it looks like different Ford models do things differently. The top spec Mondeo/Fusion with the KITT indicators has the DRLs turn off when the indicators are on, but lower spec models keep the DRLs on while the static indicators light up.

The problem is that having both DRLs and indicators so close together and lit at the same time means the indicators aren't clearly visible, but having them light up dynamically is even more distracting. Fading DRLs are also a distraction because the fading is interpreted as movement by the human brain and the driver ends up focusing on that. It's much easier to tune out static or slowly blinking lights and focus on the surrounding traffic.

It's going to be a bigger issue in the future with much smaller headlamp units that use LEDs for the main and high beams. There won't be much space so designers could cram everything together. I can imagine the cognitive horror of a road full of car lights blinking like neon caterpillars on a dark, rainy night...

Last edited by chromedome; 07-16-17 at 10:16 AM.
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Old 07-16-17, 10:09 AM   #12
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Quote:
Originally Posted by yardie876 View Post
The DRLs fading is a very nice touch.
Quote:
Originally Posted by RXSF View Post
I tend to agree but I love how Mercedes has the DRL fade back on instead of the abrupt switch back
i have yet to see this and I pay really close attention to the cars around me. Now I want to drive around until I find the feature.
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Old 07-16-17, 10:20 AM   #13
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I think it looks tacky and cheap when the LED DRL goes black to make way for an ancient halogen turn signal. If the purpose for these lights is increased visibility and safety, why not use a full LED turn signal assembly instead of halogens?
When I see Audi models with turn signals on it always seems to anger me for the reasons mentioned
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Old 07-16-17, 10:24 AM   #14
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Quote:
Originally Posted by SW15LS View Post
DRLs do NOT satisfy the requirement for headlights to be on in the rain.
The laws do mention headlights with wiper-use, but they don't mention taillights. DRLs, on most vehicles, use the same bulbs as regular headlights (without taillights), and give the same effect as headlights....at a somewhat lower intensity. In fact, I asked a Virginia State Trooper about that, because, at first, I found the law somewhat confusing, too.
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Old 07-16-17, 10:55 AM   #15
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I have an A6 and the LED DRL's are pretty bight. I can see that it might reduce the effectiveness of the turn indicators if they remained on. On my car one of the two white led strips flashes amber when the DRL switches off and it looks like most of the DRL has switched to amber.
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