Adjusting the threshold for automatic headlights

   #1  

PuJuM

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Ever since I bought my MY2016 Passat B8 it has bugged me how high the activation threshold for the auto-lights is. It feels like I'm driving around in daylight with my headlights on, burning up the bulbs and wasting 2x55 Watts of juice that could otherwise be used on my heated seats on those cold days. As many fellow drivers have pointed out, there is an option in the car menu of the infotainment (MIB) system that allows you to switch on your headlights earlier, normal or later but it doesn't seem to have a tangible effect. Similarly there is an option in the long coding of the RLS or RHLS module but this only allows you to raise the light activation threshold even higher. :banghead:

On the slightly earlier cars, possibly pre-MQB, there appear to be three channels that let you fiddle with the auto-light activation threshold, but these aren't available on my MQB car:
[table="width: 1000]
[tr]
[td]Channel Name[/td]
[td]Default Value[/td]
[/tr]
[tr]
[td]RLS_Night_Sensitivty-p_lx_rs_day[/td]
[td]500 lx[/td]
[/tr]
[tr]
[td]RLS_Night_Sensitivty-p_lx_rs_dawn[/td]
[td]200 lx[/td]
[/tr]
[tr]
[td]RLS_tunel_gateway_recognize[/td]
[td]5 s[/td]
[/tr]
[/table]
Instead there's a new adaptation channel group with 13 channels that look like they control the light activation and hysteresis thresholds.

[table="width: 1000]
[tr]
[td]Channel Name[/td]
[td]Channel Name (English)[/td]
[td]Default Value[/td]
[td]My Preferred Value[/td]
[td]Comment[/td]
[/tr]
[tr]
[td]Einschaltgrenze_CHO_LHO[/td]
[td]Switch-on limit of CHO & LHO[/td]
[td]30 lx*[/td]
[td]Default[/td]
[td]Threshold below which the coming-home and leaving-home lights are active[/td]
[/tr]
[tr]
[td]Daemmerungsgrenze, Hysterese_obergrenze[/td]
[td]Twilight limit, hysteresis upper limit[/td]
[td]60 lx*[/td]
[td]Default[/td]
[td]Threshold below which the parking lights are switched on[/td]
[/tr]
[tr]
[td]Daemmerungsgrenze, Hysterese_untergrenze[/td]
[td]Twilight limit, hysteresis lowerlimit[/td]
[td]110 lx*[/td]
[td]Default[/td]
[td]Threshold above which the parking lights are switched off[/td]
[/tr]
[tr]
[td]Helligkeitsgrenze_sehr_hell[/td]
[td]Brightness limit very bright[/td]
[td]100 lx*[/td]
[td]Default[/td]
[td]Suspected to indicate a sudden increase in brightness (such as leaving a tunnel) which reduces the time delay in switching off the lights[/td]
[/tr]
[tr]
[td]Helligkeitsgrenze_Licht_einschalten[/td]
[td]Brightness limit turn light on[/td]
[td]60 lux*[/td]
[td]Default[/td]
[td]Threshold below which the dipped lights are switched on[/td]
[/tr]
[tr]
[td]Helligkeitsgrenze_Licht_ausschalten[/td]
[td]Brightness limit turn light off[/td]
[td]110 lux[/td]
[td]Default[/td]
[td]Threshold above which the dipped lights are switched off[/td]
[/tr]
[tr]
[td]Minimale_Beleuchtungsstaerke[/td]
[td]Minimum illuminance[/td]
[td]0 lx[/td]
[td]Default[/td]
[td]Sensor calibration[/td]
[/tr]
[tr]
[td]Maximale_Beleuchtungsstaerke[/td]
[td]Maximum illuminance[/td]
[td]300 lx[/td]
[td]Default[/td]
[td]Sensor calibration[/td]
[/tr]
[tr]
[td]Minimale_Ausgangsspannung[/td]
[td]Minimum output voltage[/td]
[td]0 mV[/td]
[td]Default[/td]
[td]Sensor calibration[/td]
[/tr]
[tr]
[td]Maximale_Ausgangsspannung[/td]
[td]Maximum output voltage[/td]
[td]4500 mV[/td]
[td]Default[/td]
[td]Sensor calibration[/td]
[/tr]
[tr]
[td]Tunnel_einschalt_verzoegerung[/td]
[td]Tunnel switch-on delay[/td]
[td]2 s[/td]
[td]Default[/td]
[td]Delay before switching lights on[/td]
[/tr]
[tr]
[td]ECE_Lichteinschaltschwelle[/td]
[td]ECE light switch-on threshold[/td]
[td]1000 lx (IR)[/td]
[td]400 lx (IR)[/td]
[td]Threshold of infra-red light below which the above functions are active[/td]
[/tr]
[tr]
[td]Helligkeitsgrenze_Licht_ausschalten_red[/td]
[td]Brightness limit Switch off light red[/td]
[td]80 lx (assumed units)[/td]
[td]Default[/td]
[td]Perhaps some kind of hysteresis for IR?[/td]
[/tr]
[/table]
Observations
Now, what's interesting is that the Daemmerungsgrenze and Helligkeitsgrenze threshold channels (marked with *) are limited to the range of 0 - 255 which makes me wonder if they're actually a percentage, not lux as advertised. By contrast, the IR channels are clearly not limited to 255 as the default value is 1000 lux. I wonder what these percentage values are in relation to - could it be something to do with the maximum sensor output, although this would have to be much larger than 300 lux (as defined in Maximale_Beleuchtungsstaerke) because I've seen much larger outputs in the region of several thousand lux. You can confirm this by looking at live data. To be researched...

You may also have noticed that the two thresholds used by the Daemmerungsgrenze channels and Helligkeitsgrenze channels are actually the same. I wonder if specifying a higher threshold for the Daemmerungsgrenze channels may cause auto-lights to switch on the parking lights before the getting to Helligkeitsgrenze thresholds when the dipped beams kick in. Something I've tried to test but as yet been unsuccessful due to the relatively dark days we're having at this time of year and difficulty of using VCDS whilst manoeuvring a torch. To also be researched further...

Auto-light Function
The function of the auto-lights seems to require that: the ordinary lux reading (from the RLS or RHLS sensor) be below the values defined in Daemmerungsgrenze, Hysterese_obergrenze and/or Helligkeitsgrenze_Licht_einschalten, and the reading of infra-red lux be below the value defined in ECE_Lichteinschaltschwelle. In this setup VW appear to use IR light to enable the auto-headlight function, rather than depending on ordinary light alone. I wonder if this is because infra-red light levels seem to be much more stable than ordinary light as observed in my testing using live data. I found that reducing the threshold for infra-red light from 1000 lux to 400 lux does indeed switch the lights on a lot later! :)

Example one - stock headlights turning on at dusk
You're driving along and the day light is fading and your car is configured as stock. The readings from your RLS / RHLS sensor are currently 50 lux (ordinary) and 1200 lux (IR) so the auto-lights are currently off. As the light continues to drop, the RLS / RHLS sensor then reports 50 lux (ordinary) and 800 lux (IR) so after the time delay specified in Tunnel_einschalt_verzoegerung your dipped lights turn on. In this state the auto-lights now require either of the upper thresholds to be exceeded (110 lux for ordinary light or 1000 lux for IR light). Once this upper threshold is exceeded, a delay is introduced before switching the lights off - if the increase in light levels was large (defined in Helligkeitsgrenze_sehr_hell and sudden (i.e. leaving a tunnel) then the delay is about 2 seconds (defined in Tunnel_einschalt_verzoegerung) otherwise it's a lot longer (and I can't find an adaption channel for it). The time delay and hysteresis in the upper and lower thresholds ensure that your auto-lights are stable.

Example two - modified headlights with parking lights (needs testing)
You have set ECE_Lichteinschaltschwelle to 400 lux, Daemmerungsgrenze, Hysterese_obergrenze to 100 lux, and Daemmerungsgrenze, Hysterese_untergrenze to 150 lux. As day light fades the level of IR light drops below 400 lux (IR) enabling the auto-lights function. Depending on the reading of ordinary daylight any of the following could happen:
  • if it exceeds 100 lux then the lights remain off,
  • if it is less than 100 lux but greater than 60 lux then the parking lights switch on (needs confirming)
  • if less than 60 lux then the dipped beams switch on (confirmed)
Now these values will obviously need 'tuning' as the level of ordinary light is usually close to zero (0 - 20 lux) before IR light is anywhere near 400 lux (IR). So with these values configured the dipped lights are likely to turn on before any parking lights and only when IR light gets to 400 lux, and turn off as soon as it exceeds that value + time delay (which I can't see in any adaptation channels).

Further work
This project needs some more experimentation with real driving data or somebody who is able to control the readings from the RLS / RHLS sensor (readings are far to volatile with me using a hand torch). Only then can we confirm my suspicions of auto-lights enabling the parking lights. Any willing volunteers would be appreciated otherwise this will have to wait until spring/summer when the light levels are a little brighter as I'm commuting to and from work.
 
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   #2  

darkchina811

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I have a Golf 7 (MQB) and I also find the auto light feature to be questionable sometimes. tell me how can I help you.
 
   #3  

PuJuM

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I would love to have some additional real-world data to test my theories.

Please could you send me some measured data from the Light Recognition Sensor and and autoscan of 09, or at least the settings that your vehicle uses for the channels listed in my original post.
 
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Golf R

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Isn’t the “Earlier” “Normal” “Later” threshold in regards to how soon the lights switch on when you, for instance, enter a tunnel or tree shaded stretch of road, rather than how dark it is?
 
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PetrolDave

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Isn’t the “Earlier” “Normal” “Later” threshold in regards to how soon the lights switch on when you, for instance, enter a tunnel or tree shaded stretch of road, rather than how dark it is?
When I tried changing that setting it was definitely affected by how bright it was.
 
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jasons6930

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Apologies for the major ressurrection of this thread but has anyone got any further with this?

Getting fed up with my headlights flicking on and off going under underpasses in full sunshine!!
 
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