Let us know how it goes converting from HID to LED.
Is it doable? Sure I suppose. How far back in the headlight wiring system do you plan to replace? The factory lighting has an OSRAM D3S HID ballast in-line. There aren’t many LED bulb options in the D1S, D2S, or D3S size variant. This is because converting from HID to LED is not a conversion many people are interested in doing. Quick search shows there are some LED to HID “kits” available; some apparently just plug into an HID ballast while others somehow bypass the HID ballast? Or don’t use it? The thought of popping in an LED Bulb into a HID projector powered by an HID ballast or some sort of HID ballast LED Driver bypass “kit” just does not seem like a great solution nor a reliable one.
To be honest swapping from HID to LED in our GM trucks isn’t going to really solve your problem with light output either. The problem isn’t really the type of bulb, sure some can offer slight improvements, but the major issue is the GM bulb projector itself.
The pics below are not my vehicle, they were pulled from the GMfullsize.com forum. Although, this vehicle is a 2015 GMC Sierra, knowing GM, I’m confident that the type of projector is very similar to the ones in our Yukon’s. Sure there are probably some slight differences between the Yukon SLT Halogen projectors and the Denali HID projectors, but knowing GM I also wouldn’t be surprised if the only difference was the bulb socket. I only say this because of the clarity and still obvious projector cut-off Yukon SLT (and Tahoe owners with halogen projectors) are achieving by just swapping from factory halogen bulbs to LED or HID into their factory halogen projectors. The light pattern and cut-off typically remains the same just brighter. Definitely an improvement over stock, but only addresses part of the issue.
Let me show you what I mean... For all intensive purposes the pics from this 2015 GMC Sierra will show what I’m referring to.
Here is a photo comparison when the factory halogen bulbs in this 2015 GMC Sierra were upgraded to HID bulbs:
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Sure the light is brighter, but look at the light output and beam pattern closely. See how there is a dark spot right in the middle of the light output and beam pattern and other random dark spots. Those same dark spots are there with the halogen bulb and the HID bulb. Swapping from an HID to an LED will be no different in your ‘18 Denali. Because the headlight projector and lens omitting the light output has remained the same.
Now this photo shows going from an HID bulb in the factory projector to the same style (35W 5000K) HID bulb into a Lexus RX350 projector retrofit:
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Dramatically different isn’t it? No more dark spots, the light output is consistent and the same brightness is throughout the entire beam pattern. They’re both Morimoto 35W 5000K HID bulbs, the difference is the projector not the bulb.
Sure there is an upgrade in light output going from halogen to HID or LED. I don’t think swapping bulbs from HID to LED, and vice versa for that matter, in our GM factory projector headlights is going to make that much of a difference. You want to fix the light output change the projector and do a retrofit. Sure it’s a lot more involved and more expensive. But it’s clear from these images the weak point of our headlights is the GM factory projector in our headlights, regardless of what bulb you use.
