Before Audi awed the world with its LED daytime running lights, BMW did a similar trick with circular daytime running lights that everyone wanted on their rides, commonly known as angel eyes. But how did they light up, and did you know that they aren’t actually called angel eyes, or even halos? Let’s partially-disassemble an E90 3-Series headlight to see how BMW’s groundbreaking daytime running lights worked.
BMW’s official terminology for its daytime running lights is corona rings, which, up until 2020, was an entirely appropriate name that had no unintended negative connotations whatsoever. See, corona is Latin for wreath, and these distinctive lighting elements usually take the form of rings. I say “usually” because BMW’s designers have been on one recently, but that’s to be expected.
BMW didn’t develop this tech, instead they were the first to use Hella’s CELIS lighting technology, short for Central Lighting Systems. Originally demonstrated in 1996, CELIS started life as an interior lighting solution that used indirect lighting via refraction. A bulb simply shining on whatever you’re trying to look at is direct lighting, but Hella shined light down using translucent elements, which made the elements glow. It sounds futuristic, but it’s actually old: Guiding light via refraction was first demonstrated nearly 200 years ago by French physicist Jacques Babinet and Swiss physicist Jean-Daniel Colladon.
For a real-world example, picture those fiber optic lamps that used to be found in novelty shops. Light shines up through the fibers, causing the fibers to glow before shooting out the fiber ends. While not objectively the brightest way of lighting the way, this glow certainly is uniform, something early diffused LED automotive lighting arrangements struggled with.
A key advantage of CELIS that’s sure to appease people who say “they don’t make ‘em like they used to” is serviceability. Most modern headlights with LED daytime running lights aren’t designed so that you can easily replace an element if it burns out. You have to break into the headlight housing, whip out your soldering equipment, and go to work like you would on an old electronic device.
BMW’s use of CELIS employs filament or halogen bulbs with their own little reflectors, meaning that if a corona ring were to go out, it’s a relative doddle to change. Either swap them out for stock replacements or do what the previous owner of my 3-Series did and throw in some LEDs. I’ve played around with both and can definitely say I’m a fan of the warm tinge the stock bulbs have.
Soon after corona rings came to the facelifted E39 5-Series, the aftermarket went nuts for them. While CELIS was Hella’s technology, a universal aftermarket solution for those looking for the angel eye look soon came in the form of CCFL rings, short for Cold Cathode Fluorescent Lighting. Instead of traditional filament bulbs, these lighting elements use excited electrons, mercury vapor, and a phosphor coating to provide a uniform glow without melting plastic headlight housings. While great-looking, CCFLs have largely fallen out of fashion due to advancements in LED technology.
Pretty much every new styled daytime running light you see today whether OEM or aftermarket uses diffused light emitting diodes that are efficient, long-lasting, and a much cooler light than you’ll get out of a halogen bulb. As a bonus, they’re now relatively cheap to manufacture and way brighter than CELIS. The brightness cuts two ways though, as many drivers of newer cars simply motor on at night with nothing more than their daytime running lights illuminated.
While the aftermarket latched onto angel eyes like a snapping turtle, it’s also worth noting that a huge array of manufacturers have used a variation of BMW’s circular design, from Mazda to Chevrolet. With the performance of projector headlight elements established, it’s likely a look that’s here to stay.
Hopefully you found this look into BMW’s pre-LED corona rings illuminating. We’ve certainly come a long way since sealed beams, and it’s likely the next few decades will spawn new innovations in lighting. Can America hurry up and approve proper, full intensity matrix headlights already?
(Photo credits: Thomas Hundal, Amazon, Chevrolet, Mazda)
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Thankfully, BMW learned the lesson of the E90 by the time they got to the E82/E88 and moved the halo bulb (now a bog-standard H8) to the center of the headlight cluster – remove the back cover, pull the wire plug, turn, and remove.
Nice. I really enjoyed this read as I updated my E85’s headlights with angel eyes and the car looks much more modern after that. My other car is a Camaro like in the photo, and the DRLs give so much character to the car.
“The brightness cuts two ways though, as many drivers of newer cars simply motor on at night with nothing more than their daytime running lights illuminated”
A major annoyance for sure. Drivers who do this don’t pay attention (or don’t care) which also means they’re driving at night on their DRL’s with their taillights and marker lights turned off. This also illustrates how little salesmen care about showing customers how to operate the basic features of the car they just purchased because there are obviously people who no longer know how the light and wiper switches work.
Thank you! So many times Audi gets the credit for introducing “light signatures”. BMW did it first and best – these weren’t some random squiggles tossed inside the housing either – the rings were an extension and accentuation of BMW’s long-lived quad round headlights, which by that point were already the most recognizable lighting elements. Corona rings were icing on the cake.
This reminds me, what’s going on with the Mercedes Wagon @MattHardigree? Project something-or-other?
Wassup with that?
I became very good at swapping out the angel light globes on my E90 330i after I baulked at the price of an official replacement globe (something like AUD$180 from a local independent BMW mechanic) and bought cheap LED replacements instead… Which failed after about a month. So I bought a second, slightly more expensive set… Which failed after two months. After that I bit the bullet and bought an official globe for about $70 from an eBay seller based in Latvia of all places, which did the trick and returned the lights to their “classic” yellow hue.
One thing that annoyed me about the job was you had to remove all the plastic under the wheel arch to get to the bloody thing, which I initially did with the wheel removed but eventually worked out you could do it at full-lock. This was especially annoying as the main beams were behind a much simpler little service hatch that for some reason didn’t extend to the angel lights.
I’m now glad I sold the car before the presumably more expensive xenon main globes failed.
The only ones that bother me are the halos on Jeep headlights. They always look so wrong.