HID Bulb Types and Identification – D1S D1R D2S D2R D3S D3R D4S D4R etc

You may have seen references to various D-Series HID (xenon) bulbs in the context of projector swaps, D1S, D1R, D2S, D2R, D3S, D3R, D4S, D4R, sometimes even D2C and D2H. So what’s the difference?

All of these bulbs have the quartz envelope and arc positioned in the same place – so any D-series projector can use any D-series bulb by bending/cutting out the indexing tabs. For example, if you buy a AL Gen2 projector from an Audi but want to use aftermarket D2S bulbs + ballasts, just bend down the key tab! Please don’t use D*S bulbs in reflector headlights as it will effectively be a high beam!
HID bulb types. Read more about them in this HIDPlanet thread. ECG is the technical name for ballast. All aftermarket ballasts are designed to use D1 and D2 bulbs only, and will not operate the other bulb types.

D-Series Naming System

D-Series bulbs are named using 3 characters, like “D1S”.


D - "Discharge"
N - 1,2,3,4 is the type
T - S is for projector, R is for reflector

To illustrate this

1. Ignitor: integrated (D1*, D3*) vs. separate external (D2*, D4*)

The D1 and D3 bulbs have an integrated ignitor (silver box) on the back of the bulb. D2 and D4 bulbs use ignitors that detach and stay with the headlight.

Igniter built-in: D1, D3
No integrated ignitor: D2, D4

2. Voltage: mercury (D1*, D2*) 85V vs. mercury-free (D3*, D4*) 42V

Mercury bulbs (D1S, D1R, D2S, D2R) run at 85V AC. Mercury Free (hg free D3S, D3R, D4S, D4R) bulbs run at 42V AC.

3. D*S is used in projector vs. D*R is used in reflector headlight with shield on envelope glass

S series bulbs (D1S, D2S, D3S, D4S) are used in projector lamps, R series bulbs (D1R, D2R, D3R, D4R) are used in reflector lamps.

Bulb Identification

What if you are given D1R and D3R or D2S and D4S without label? You can’t see if there is mercury inside (and thus the voltage). It is possible to differentiate using the notches on the bulb.

Location of notches on D-Series bulbs
This diagram shows the notches on the bulb base, looking at the bulb, as well as the location of the notch on the lamp holder (in red)

Aftermarket Bulbs

Again, all of these bulbs have the arc in the same place, so to reduce the number of different models to produce aftermarket manufactures have developed the D*C type, which universally fits multiple notches. For D1/D3, a removable ignitor adapter is available.

5 notches? What is going on?? These are “Type-C” bulbs
4 and 5 notch D-Series bulbs are type “C”

Aftermarket manufactures don’t want to make a lot of different models. D2C that can replace both D2R and D2S. D4C for D2S, D2R, D4S, D4R and D2C. D1S with 5 notches won’t be hard to understand.

D2C replaces D1S and D2S, D4C replaces D3S and D4S

All of this makes it simpler for production, but much more complicated for consumers… And most sellers even don’t know about the real reason or the difference.

C-type bulbs with integrated ignitors can be differentiated by the keying on the ignitor connector

Another way to differentiate D1S vs D3S is based on the keying in the ignitor connector.

Finally, the last aftermarket type is sometimes called “D2H” which includes AMP connectors for aftermarket ballasts. It is always 85V / Mercury.

Aftermarket bulbs (used when the OEM ballast fails, or for projector swaps) with AMP connectors are sometimes called “D2H”, and have enough notches to fit anything.

Many thanks to this post, and the HID planet thread.

AL Gen2 Projector “de-key” Modification

You can easily modify AL Gen 2 projectors to fit any of the D base bulbs by bending the key tab out of the way (aka dekey the projector):

This is the key tab that prevents using a D2S bulb in a D4S or D8S projector
Key tab partially bent on an AL gen2 projector
Finishing the bend, using pliers to curl it completely out of the way
When complete, the back should look like this.