LED CHMSL - 3rd brake light

I replaced the center high mounted stop light (3rd brake light) in my 2016 GMC Sierra pickup with the Philips 921 LED. I was concerned about how a 6000K light would look behind the red plastic lens. I had heard it would look pink, light brown, etc. But to my surprise, it looks fine. Compared to my stock LED brake lights, you really don't notice much difference, unless someone has pointed it out. If one was to nitpick, you "might" could say it has the very slightest reddish-orange tint, but the casual oberver would not really take notice. See attached pic.

No good. Despite that you think it looks OK, it is not. That bulb does not put out enough red light to give safe performance in a red-lens CHMSL. Take it out and put the correct bulb back in.

moodysj said:

See attached pic.

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Pictures don't tell enough of the story-- and our own eyes really can't, either. Sure, it lights up, but lighting up isn't enough. It needs to meet certain standards of performance, like the EPLLA (effective projected luminous lens area) and exceed certain minimums at certain test points while staying at or below certain maximums at those and at different test points.

The 6000K CCT of that particular bulb means that light at the other end of the visible spectrum is attenuated-- you're not getting the red you need to really get the light you need out the lens. Remember, the red lens the light is shining through isn't converting white light to red-- it's stripping the non-red light from the bulb's output.

What CCT would you recommend for a replacement?

There is no legitimate LED bulb for this CHMSL.

-Virgil- said:

There is no legitimate LED bulb for this CHMSL.

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Could the assembly be swapped for a purpose-made LED CHSML, from GMC or a third party, I wonder?

(Apart from colour, that photo seems to show the other issue to be expected, the output of that LED doesn't fill the width of the lens. All the LED CHSMLs I've seen have a strip of red LEDs for that reason)

markweatherill said:

Could the assembly be swapped for a purpose-made LED CHSML, from GMC or a third party, I wonder?

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Absolutely!

Of course, if you leave the original CHMSL installed, disable it so that you have only one CHMSL.

Hella makes some LED CHMSLs for interior mounting, but they are designed for window angles from 20°-80° (they have three kinds covering three ranges), so you'd have to get creative with the mounting of the 57° to 80° one to make it more parallel with the back glass. Not too difficult, really.

Or, you could find a GM LED one to fit the exterior location, if they make them.

markweatherill said:

Could the assembly be swapped for a purpose-made LED CHSML, from GMC or a third party, I wonder?

Click to expand...

Sure! All you have to do is make sure to get the angle right. It needs to be mounted at the angle it was designed for; there is essentially no leeway on this.

They do make aftermarket LED CHMSL assemblies for trucks. Why these newer trucks have LED Tails, but still stick with Incadescent CHMSL, when LED CHMSLs have been around for 17 years or so, (the 2000 Cadillac DeVille was the 1st car to have LED tails) the 2000-2005 Chevy Impala was one of the 1st cars with LED CHMSLs, so why trucks continue to use Incadescent CHMSLs is beyond me. Point is, if it is a 921 bulb setup in any coloured lens, stick with Incad. as no legit RED LED 921s exist (not that i know of). If you want LED CHMSL, see if a OEM one exists as it would be cheaper than a aftermarket one anyway, or get a Aftermarket assembly, however I have heard people get sealing issues with those units, and water leaks in.