Projectors: HID vs Halogen; DOT vs e-Code

While doing research for a possible HID projector upgrade for my 2003 Jetta wagon, I found found many posts saying that headlight projecters are designed differently for halogen vs HID, and that it would be bad to install HID bulbs into halogen projectors. This didn't make sense to me -- a projector is a projector, right? But nobody that I found actually said WHAT was different.

So now I've educated myself, and I'm here to explain it to you. In a nutshell, a projector designed for halogen bulbs concentrates the light in a spot directly ahead, while HID projectors cast a fairly even semi-circular flood.

Here's the headlight pattern from my 2005 New Beetle factory halogen projectors:


Here are some examples of HID projector patterns. These are all e-code beam patterns, but a DOT beam pattern would have the same even flood of light, just in a different shape. Some of these projectors are a bit out of focus and exhibit a darker center. This is probably a quality issue with the projector or bulb, but it might be correctable with a thin spacer between the bulb and the projector (or a spacer might make it worse).





I ordered some headlights off eBay advertised as HID for my Jetta wagon. I found that they had a DOT halogen projector, not the e-code HID pattern I was expecting. A dead giveaway is the electrode shadow -- an HID projector would spin the bulb to get the electrode out of the beam. Since the projector lens flips everything upside down, this photo shows the electrode on top. Putting the electrode on the bottom would eliminate the shadow. Note the DOT pattern: mostly flat on top with just a little step up on the right.


So what's wrong with putting an HID light into a halogen projector? Here's where I speculate a bit. An HID bulb puts out 3-4 times as much light as halogens. So halogen projectors focus the light in a spot up front, where you need it most. By contrast, HID emits enough light to create a flood and still illuminate directly ahead sufficiently.

Flashing your lights in other drivers' eyes, even with properly adjusted projectors, is sometimes unavoidable, especially in hilly areas. With regular headlights and halogen projectors, the light will be annoying, but not blinding. But if you have an HID bulb in a halogen projector, most of the light from the HID bulb will be concentrated in a spot. This is enough to blind other drivers if the beam hits them.

If you have a set of projector headlights designed for halogen, and you want to upgrade to HID, you can do so by getting a pair of salvage HID projectors that fit your headlights. While the details of this are beyond the scope of this post, you can get info and projectors from a place like The Retrofit Source, or hit the junkyard and scavenge projectors from high-end cars. Replacing the projectors will probably cost roughly $50-$150 and will require removing the headlight lens to get access to the projector.

When I was trying to figure this out, one theory I had was that halogen and HID bulbs place the light source at different distances from the base, so that installing the wrong bulb would result in an out of focus beam. This turned out to be false. When I tried halogen and HID bulbs in the same headlight, I got the same beam pattern either way. Also, this photo shows that the light sources are pretty much the same distance from the base either way.


Here's a link that shows the difference between a DOT and e-code (ECE) beam pattern: https://www.retrofitlab.com/blog/dot-vs-ece-beam-pattern/

I hope this helps someone -- I couldn't find this info explained plainly anywhere else.

Thanks for consolidating this information. I had been wondering some of the same things.

I had picked up a few different sets of aftermarket/eBay headlights & 1 set of retrofits, but have done nothing with them & traded away some of them.

But recently picked up the Xenon projector assemblies from a BMW 330ci with hopes/plans of making my own.

I have lots of questions, but this has helped answer some of them. Thanks again.

You're quite welcome, Rex. Feel free to post your other questions here, and maybe I or someone else will be able to answer them. Also, please see my other post and give me advice, if you can.

shoebear said:

While doing research for a possible HID projector upgrade for my 2003 Jetta wagon, I found found many posts saying that headlight projecters are designed differently for halogen vs HID, and that it would be bad to install HID bulbs into halogen projectors. This didn't make sense to me -- a projector is a projector, right? But nobody that I found actually said WHAT was different.

So now I've educated myself, and I'm here to explain it to you. In a nutshell, a projector designed for halogen bulbs concentrates the light in a spot directly ahead, while HID projectors cast a fairly even semi-circular flood.

Here's the headlight pattern from my 2005 New Beetle factory halogen projectors:

Here are some examples of HID projector patterns. These are all e-code beam patterns, but a DOT beam pattern would have the same even flood of light, just in a different shape. Some of these projectors are a bit out of focus and exhibit a darker center. This is probably a quality issue with the projector or bulb, but it might be correctable with a thin spacer between the bulb and the projector (or a spacer might make it worse).

Click to expand...

That's not a HID projector. That's a crappy h1 projector with a H1 HID kit installed.

Note the DOT pattern: mostly flat on top with just a little step up on the right.

Click to expand...

HID projectors have the flat top to the right. both ecode and DOT. the size of the step & shape of the step varies.

In some cases there are no differences between a DOT and ECE HID projector, such as the hella e55 bixenon.

Hella E55 bixenons have their bright side centered, for distance especially with their high beam. The sides aren't as bright, as the reflector is designed with that bright side with a rougher coating to the sides of the reflector.

20IndigoBlue02 said:

HID projectors have the flat top to the right. both ecode and DOT. the size of the step & shape of the step varies.

In some cases there are no differences between a DOT and ECE HID projector, such as the hella e55 bixenon.

Click to expand...

This page was one of my sources. Headlight Services - FAQs

20IndigoBlue02 said:

Hella E55 bixenons have their bright side centered, for distance especially with their high beam. The sides aren't as bright, as the reflector is designed with that bright side with a rougher coating to the sides of the reflector.

Click to expand...

Here's a photo of the Hella E55 low beam pattern:


and here's a Hella E55 high beam pattern.


Some observations

• My original comments were all about dedicated low beams. High beams are indeed a different matter, and most high beams concentrate light straight ahead down the road.
• Although I haven't looked closely at bi-xenon projectors, I think they work by sliding their light curtain up and down. As such, there might?? be some compromises between low and high beams, since one projector does both. This could explain why the E55 low beams have more of a "spot" on them than a dedicated low beam projector.
• Even with the "spot", the E55 low beam distributes light much more evenly and widely than a halogen projector.

not all projectors, whether they are halogen or HID cast a semi-circular beam pattern. Many projectors can have a foreground limiter (a shield on the upper part of the assembly).



which results in


The old 2.5" Valeo H7's in Audi A4's also had a foreground limiter built into the cutoff shield.

Also a common Koito H11 assembly found in many Japanese cars have a foreground limiter

20IndigoBlue02 said:

not all projectors, whether they are halogen or HID cast a semi-circular beam pattern. Many projectors can have a foreground limiter (a shield on the upper part of the assembly).

Click to expand...

OK, good to know. But even if a (dedicated low beam) Xenon projector has one, I would expect its beam to be fairly even, without a significant hot spot directly ahead.

Both the Valeo H7 and the Koito H11 are bi-xenons. Here is a video of the Valeo H7 in action: https://www.youtube.com/watch?v=3QvcThwg6SU

But my basic premise remains the same: A true Xenon HID projector should cast a mostly even flood of light compared to a similar halogen projector. Bi-xenons apparently compromise some of this evenness because one beam does double duty. However, even they (on low beam) are more even than halogen projectors. Foreground limiters may cut off the bottom of a beam as well, but the basic beam, however it is shaped, should be a pretty even flood, especially in a dedicated low beam.

Do you agree with this? If not, can you explain the essential different between a projector designed for halogen vs one designed for HID? For example, would it be a bad idea to put HID's in my Beetle's headlights? If so, why?

shoebear said:

... put HID's in my Beetle's headlights? If so, why?

Click to expand...

I need to snap some pics to confirm, but I recall when I was comparing the Xenon HID assembly from some BMW 3 series, they appeared to use the same mounting holes/size/shape as the halogen projectors in NB headlights.

I realize the "depth" may be different, but I wondered if it would provide an easier Xenon/HID option for NB owners, but since I don't have one, I didn't investigate any deeper.

I'll try to get some pics & dimensions of them this evening.

Thanks, Rex. I'm mainly interested in getting HID's in my 2003 Jetta wagon. My window of opportunity for this, however, will end in about a week, and the HID headlights I ordered turned out to be halogen projectors with an HID 'bulb slap" retrofit, so I'm returning them. I have another thread about that; I'm trying to keep this thread more abstract about the general design differences between halogen and HID projectors.

However, if I succeed with installing HIDs in the Jetta, I may try the NB next. So maybe post the BMW 3 series info over there? I have no replies yet, so maybe you can help bring that thread back to life.

I guess my question/theory wasn't clear in my ramble above.

It would go against most of the information I've read to discover the projectors used in NB Halogens and BMW Xenons were the "same".

Until I can do a more complete comparison, I have to speculate that at least the lens in the assembly is different.

Hope that makes more sense.

RexNICO said:

I have to speculate that at least the lens in the assembly is different.

Click to expand...

I agree. The premise of this thread is that halogen and HID projectors are fundamentally different in design, and to help identify exactly how that difference shows itself in the beam patterns.

shoebear said:

OK, good to know. But even if a (dedicated low beam) Xenon projector has one, I would expect its beam to be fairly even, without a significant hot spot directly ahead.

Both the Valeo H7 and the Koito H11 are bi-xenons. Here is a video of the Valeo H7 in action: https://www.youtube.com/watch?v=3QvcThwg6SU

But my basic premise remains the same: A true Xenon HID projector should cast a mostly even flood of light compared to a similar halogen projector. Bi-xenons apparently compromise some of this evenness because one beam does double duty. However, even they (on low beam) are more even than halogen projectors. Foreground limiters may cut off the bottom of a beam as well, but the basic beam, however it is shaped, should be a pretty even flood, especially in a dedicated low beam.

Do you agree with this? If not, can you explain the essential different between a projector designed for halogen vs one designed for HID? For example, would it be a bad idea to put HID's in my Beetle's headlights? If so, why?

Click to expand...

The Valeo H7's used on Audi A4's were not bifunction. THey were for low beams only. The Koito H11's are only low beams, as you can see in the shield.

The cars I've driven with Koito H11 projectors have a wide bright spot.

Reflectors for the bulb, have different designs, which is dependent on the performance criteria for the lamp. Some low beam only projectors are made for distance. Some are made for for width, some are a combination.

I had a S2000 low beam retrofit on my old MK4 Golf. Those projectors are made for width.

I've put HID's in my old Passat with 3" Valeo H7's. It wasn't that bad, the HIDplanet folks liked beam pattern as a result. I was in the middle of a e55 Evox-R retrofit until I traded the car in. HID's in your beetle? Won't know how good it would be until you tried it. At least get a ballast that you can swap connectors, from AMP to D2S, in case you decide to use a Bosch-AL E46 projector later.