DRLs & LED Bulbs

[romad]

I have E-code Headlight assemblies and use H4 bulbs in them. The DRL circuit uses the low beam filament at a reduced voltage (BTW, anyone know the lower voltage). Has anyone replaced H4 bulbs with LED H4 replacements and have the DRL's still work properly?

 

[Lug_Nut]

The LED replacements will be nearly as bright as DRL as for headlights.
The voltage reduction for use as DRL is created by a 'series resistance wire', nothing more than a long length of small gauge wire that has about 1/3 the internal resistance as the incandescent filament. The 12 volts to the headlights now has another resistance to pass through before getting to the headlight. The result is about 4 volts being used to 'illuminate' the series resistance as infrared heat and about 8 volts being the potential at the filament.
The LED will use so little power that the small gauge series resistance wire is effectively no resistance to that greatly reduced amperage draw. There'll be next to no voltage drop at the ends of the resistance wire leaving nearly the full 12 volts at the LED capsule.

 

[Nuje]

The voltage reduction for use as DRL is created by a 'series resistance wire', nothing more than a long length of small gauge wire that has about 1/3 the internal resistance as the incandescent filament. The 12 volts to the headlights now has another resistance to pass through before getting to the headlight. The result is about 4 volts being used to 'illuminate' the series resistance as infrared heat and about 8 volts being the potential at the filament.
The LED will use so little power that the small gauge series resistance wire is effectively no resistance to that greatly reduced amperage draw. There'll be next to no voltage drop at the ends of the resistance wire leaving nearly the full 12 volts at the LED capsule.

This is a FANTASTIC explanation of how the DRL circuit works in these cars!
I always did fine with high school physics until we got to electricity. Explanations like this help me immensely.

 

[romad]

The voltage reduction for use as DRL is created by a 'series resistance wire', nothing more than a long length of small gauge wire that has about 1/3 the internal resistance as the incandescent filament.

Ah, that must be wound inside the heatsink at the base of the bulb. I may try an experiment by replacing the right side H4 bulb with an H4 LED, then compare the headlights in the DRL, low beam, and high beam settings.