The wife drives an 09 Venza with DRL. When running on DRL the halogen bulbs are driven via PWM to dim the light output. Recently we put LED bulbs in and the DRL is basically full brightness on LED's. Of course PWM is a good way to dim LED's but it seems they are just bright as all get-go. I'm wondering if anyone knows a solution to this other than putting halogen back in. I like the LED Headlights. They're plenty bright, brighter than halogen for sure.

The headlamp assemblies are projector type with internal Choke Plate so as to not blind oncoming drivers. The CP is fixed (doesn't move). For High Beams there is a second lamp assy. is a basic reflector type. And when THOSE LED's are lit - they - um - well, I think I understand the expression in a whole new way; "Let there be light". And there was light. And it was bright as snot!

Not concerned about HB's, just want DRL to be on yet not at such bright levels. Also, I don't know how DRLs will affect the LED lamp. It has a cooling fan, so there's a chance it might not be cooling as much as it should. Especially in the desert heat. Today alone is forecast to hit 102˚F in the Salt Lake area. The only current option is to not engage DRL's. But that means not having the headlights set to Auto. Still, I like the DRL for visibility. The car is white so DRL might not be quite so important. DRL on my 17 Tacoma is not a problem. So I can't copy that.

What ideas do you have?

 

One thing that comes to mind is to add a circuit that detects the PWM signal which then adds a series power resistor to reduce the LED intensity.

More complex is to add a circuit to detect the PWM and use a one-shot with a series MOSFET to shorten the PWM on-time.

Either of those sound feasible to you?

 

Yeah, sounds like it's plausible.

Been looking at the harness. Hate to cut into it. But sometimes you gotta do what you gotta do.

 

sounds like it's plausible.

Do you have a preference over the added resistor versus modifying the PWM duty-cycle?

If you want to modify the duty-cycle, will need to know the present PWM frequency and duty-cycle (approximately).

 

A resistor and a relay sound most plausible. Will have to give it more thought.

Years back I did some diode to diode logic along with some relays. The main reset relay was connected one lead to the brake pedal light switch while the other lead was connected to the brake light. When there was no power the relay could stay locked because another relay was holding it latched. When the brake pedal was pressed the relay was fed 12V+ to both leads and it would drop out. Or something like that. Was back in the early 80's and I don't remember the schematic. Its purpose was to start the car then activate the circuit which held the ignition on even though the key could be turned off and locked. If someone managed to get in - the steering wheel was locked, the shifter was locked and if they stepped on the brake the engine would cut off. Only if the key was in and turned on would the engine keep running.

I'll have to give this all more thought. Right now I'm feeling the effects of the heat. It's a hot one here today.

 

A resistor and a relay sound most plausible.

Then need to know the lamp current draw.

 

Please consider the possible negative effect of shining more glare into the eyes of oncoming traffic!! Around here it is fools driving with their fog lights on, to somehow "provide more safety. " How does shining glare in my eyes improve safety???

 

Around here it is fools driving with their fog lights on, to somehow "provide more safety."

Relax Billy boy, you and I are in different states. You're as safe as can be. I may be a fool but I'm a QUALITY fool. Other fools crave to rise to my level. And since it's apparent I don't care about others - why am I asking to limit the amount of potential blinding light.

Oh, wait! We're talking about daytime running lights. If your eyes are that sensitive to light then put on sun glasses. And stop with the insinuations. Read the title! "Is there a solution? Daytime Running Lights." DAYTIME.

How does shining glare in my eyes improve safety???

FYI: my headlights do not shine beams of glaring light into night time oncoming traffic. I've worked in the Quality end of electronics for some 40 years. Doing things RIGHT is in my nature. At night I'm not blinding anyone. It's just that I've noticed that the lights are on practically full brightness. Given that DRL's are often controlled by PWM I am not a fan of taking and dimming a lamp that wasn't designed to be dimmed. It's not the first time I've dimmed non-dimmable LED lights. So the course of wisdom in this case is to ask those who know more about this stuff than I do if there's a solution. But if all you want to do is cast dispersions on me - put me on the iggy button. Please. That way you don't get irked by my foolish questions.

 

I've seen those idiots who put HID and LED lamps into standard reflector headlamp assemblies. Those are the ones you can't escape the night time glare. Those are the ones who hear "Use LED" or "Use HID, you'll be amazed at how much light you can throw." And yes, they DO cast blinding glare. I have a very low tolerance for stupidity. So on the road I find myself rather disturbed when I encounter those who don't know what they're doing but do it anyway, not realizing the consequences of safety. I'm not one of them.

 

IF you are able to access the PWM circuit output, and IF it is a separate circuit providing the PWM, then a series resistor could be a simple solution, although not a small one. OR if the PWM is generated by a separate package, (not likely) then a resistor in series with the supply feed to that circuit. Not efficient, but more reliable and much simpler.

Sorry about the ranting!!
The original DRL requirement came from a nearby country that had three lane highways, with the center lane for passing, AVAILABLE FOR BOTH DIRECTIONS. This lead to quite a few high-speed head-on impacts. The intention was then to require that the headlights be on so that the drivers might avoid the impacts. That was much cheaper than repairing the 3 lane highways.

 

Just to be clear, my understanding is that the PWM signal is to reduce the light intensity during daytime when they are used as running lights, and they operate at full intensity with no PWM at night.
Is that correct?

 

Just to be clear, my understanding is that the PWM signal is to reduce the light intensity during daytime when they are used as running lights, and they operate at full intensity with no PWM at night.
Is that correct?

Correct. IF PWM is incorporated. DRL is headlights just dimmed down.

 

Dimming LEDs is often a challenge because of the very nonlinear diode function. In a car with the OEM dimming function buried in an expensive module, changing the duty cycle of the original controller is probably not possible for most of us. A separate PWM controller would allow quite a few interesting modes of operation, including variable brightness headlights. BUT that would also require driver control and a lot of changes in the wiring and interface hardware.

In this instance it seems that a SPDT relay to provide battery voltage thru a resistor, when active, and a connection to the original headlamp feed when not active, would be the simplest and most reliable scheme. The question being the resistance and power rating of that resistor. Probably a bit of experimenting will be required.

 

In my mind the big challenge is to have dim lights during the day but when night falls the headlights go full bright. The question would be "How easily can I further dim the DRL function and still have full brightness at night when darkness automatically switches headlights on?" I'm not seeing a way around that. Accessing the PWM function of the automotive electrical system is not something I want to chance messing with. Damaging the computer could cost hundreds of dollars.

And the idea of having DRL powered from an outside PCB comes with the fear of back feeding the computer. It probably shouldn't cause any issues - but I don't know that for a fact. It may end up being something I just live with.

 

n my mind the big challenge is to have dim lights during the day but when night falls the headlights go full bright.

My thought is to detect the PWM signal and have a relay add a resistor in series with the PWM signal.
When the headlights go full bright with no PWM, the relay removes (shorts) the resistor.

Sound feasible?

 

Mostly it sounds feasible. However, it's building a detector circuit that is beyond what I currently know.

Just tried a capacitor across the leads. The cap used was one of those "Anti-flicker" caps used on HID systems. Unfortunately it didn't reduce the flicker. My reasoning was a cap would smooth out the pulses. When asked for full illumination the cap would charge up and the light would remain illuminated. Unfortunately, the cap may have smoothed it out but not to a sufficient degree.

I shot a video of the flicker and the lights would appear to come on then go off, then on, then off. On, off, on, off. Clearly it's PWM. The reason for the video aberration of ON / OFF / ON / OFF is due to the camera aperture rate. Part of the time the light appeared to be on and part of the time it appeared to be off.

 

Was just looking for an anti-flicker kit for LED DRL but didn't find anything. My search is not yet over though.

HOWEVER: I did find LED headlights that claim to be DRL compatible. I'm going to do some more searching on that.

 

What does it mean when it says it's CAN Bus ready?
https://www.amazon.com/AUXITO-Bulbs...8PM5FG/ref=sxin_17_pa_sp_search_thematic_sspa.
Does this mean it's DRL compatible? I saw one that said "DRL Ready"
https://www.amazon.com/Anyhut-Daytime-Running-Universal-Vehicles/dp/B0DXVB4WM3/ref=sr_1_8
But it has a very low rating (2.9 stars out of 5)
And it looks cheap too.

 

So you have two problems: flicker and brightness?
I'm a little confused now.

 

Unfortunately this guy didn't directly answer my question.