low beam is too dim
 

I have a 2009 tC with stock headlight setting (reflector housing for high beam and projection for low beam). The low beam is too dim, almost at a point not to drive safe on unlit roads.
I have restored headlight clarity, tried new halogen, new HID and new LED for lowbeam (H11), and all of them failed to produce decent illumination. This got me to suspect that the problem is not with lights, but somewhere else.

My high-beams are halogen (9005), DRLs are cheap T10 LEDs. Does mixing LEDs and halogen causing any trouble? One thing I noticed is that when turning on high beams, the DRLs do not go off. Don't know if that's normal.
High beams illuminate well, by the way. It's the low beam that's bad.

Any suggestion where to start looking at? I'm new in tC world, so need your help badly.

are they the factory headlight or an ebay/aftermarket headlight? its possible that the projector itself could be misaligned.

There should be aiming adjustment screws on the back of your headlight, try adjusting them.

Thanks. They are factory headlights, I just tried few different aftermarket low beam bulbs (HIDs and LEDs).
The alignment could be shot, I guess, but would a bad alignment cause dim lights?

I'm aware of this issue from LED conversions on bikes. When you added the LEDs you created a load imbalance. Adding LEDS (DIY) needs the addition of resistors to balance the expected levels of resistance in the circuit. I can't tell you how to fix this since you've created a 3 headed hydra in your front lights but if you're committed to that config, google "LED load balancing resistor" or something along those lines, and buy a soldering iron.

Plus side: resistors are dirt cheap, this has nothing to do with the car.
Minus side: You'll need to calc the resistance you need to balance the lights.

One thing I did last night, took a multimeter and checked voltage in both headlights. They are getting 12V each. Also checked the low beam fuses, and they are 12V, too. So, at least no imbalance in voltage. I will check out the LED imbalance thing though.

If you swap in normal halogens does this fix the dim low beams? If it does you have no problems with the car, just your current setup.

Here's a silly but true example of the difference between voltage and current: I have a John Deere lawn mower that will not start. Take volt meter on starter solenoid, hot post reads 12V. Turn key to start, starter doesn't go. Bridge hot post to starter post, starter doesn't go. Bad starter? No. When I tested the hot post with a test light to ground, it didn't light. 12V on the post but no light. Result: 12V + cable from battery was heavily oxidized and while the wire provided 12v, it didn't provide enough current to light a flashlight.

So anyway, this isn't about there being 12V at the hot leads.

I would troubleshoot your issue by popping in stock bulbs until you isolate the specific problem spot.

Normal halogens are dim too. That's why I wanted to upgrade to HID/LED in the first place :(

I've got nothing at this point :(

Me too. I've aligned the headlights properly and checked voltage. They are fine. Tried back the halogen bulbs, but same dimness shows. I guess the wiring could gone bad and can't carry enough amperes? I don't know.

Would using a relay to directly power the headlights from battery help?

I tried a relay harness, and the dim outputs remains the same.
So, I looked into the projector lens and both of them are kinda foggy and have spots in them. Now I feel like the projector lenses are dimming my light.
Does anyone know if the fog/frost appears inside the lens or outside the lens? I am thinking of cleaning it in place, without taking the whole headlight assembly out.

If the seal on the headlight assemblies is compromised, you will get water vapor inside, inside fogging, etc. One of my headlights has this issue and I haven't taken the time yet to reseal it.

The inside of headlight looks pretty clean and dry. But I'm interested in the projection lens only. Do you think it can have frost outside of it?

Maybe a bad coating on the projection lens itself? Heat and oxidation accelerated... like a 10 year old aluminum wheel.

Still struggling with low output from low beams. Tried halogen, LED, HID and used relays to power up HID directly from battery, still the same.
One thing I noticed: when I turn on the lights, for a split second it is really bright and then goes back to low output again. It's very fast, but I noticed it. Does it indicate anything? Like for some reason, it is not outputting the usual light amount?

have you tried to use a headlight relay harness?

Yes, I am using relay harness currently with HID bulbs. Same result.