So you are looking to replace your OE bulbs eh? This thread will have some basic information on High Intensity Discharge (HID) bulbs and why you shouldn't cheap out and should shop smartly and informed. First off, how do you know when you need to replace your bulbs? It is probably not when you think. With halogens (oldschool bulbs that have been on and continue to be on cars for forever) it is quite simple. When the light goes out, the bulb needs to be changed. This is NOT true for HIDs. The quick answer is to replace them once they stop cold igniting. You may notice that your bulb doesn't "turn on" with the headlights. However, you may notice that you can turn them on and off a couple times in quick succession and it will work again. Most people attribute this to a vehicle problem with those "new fangled fancy lights". It isn't. That is the failure mode of HID bulbs. These bulbs do not have an easy life like halogens do. They are subjected to high stress and voltages on startup. This slowly erodes the electrode near the salt chamber (more on this later). As it slowly erodes the gap between the cathode and anode increases slowly. Eventually the gap becomes too wide for the turn on surge to pass, and you have an open circuit, no juice flows, no light comes out. However, a bit of charge remains and the salts might have just got zapped slightly warming them up along with all the bulb. When metal gets hot, it grows slightly. When you are in this electrode length of starting and maybe not starting temperature plays a factor. If you flick them on and off enough, eventually it might get hot enough to jump the chamber and start the ignition process. It may buy you a couple days, a couple weeks, or months. But you need to replace your bulbs when this happens. Assuming you drive with both headlights on at the same time, you will want to replace both bulbs even though only one is showing the problem. Also since this is PriusChat, if you have older D2R bulbs instead of the newer (2006+) D4R bulbs, your bulbs contain trace amounts of mercury in them and should be disposed of properly, not just thrown into the trash. Why replace bulbs on first sign of failure? Well simply put, it is bad for the entire system otherwise, and best case scenario is that you are gambling with your ability to reignite a bad bulb when you need to see. A halogen bulb is simple with one or more (2 in the Prius) filaments that glow when you send DC voltage through them and the surrounding gas. The gas is a halogen gas (obviously) and the filament is usually tungsten. Very similar to incandescent lightbulbs that you shouldn't have in your house anymore . You can make the DC voltage smaller and the bulb will glow dimmer, make it higher it glows more. You can take some AA batteries or a 9v or a car battery, hook it up to the bulb and voila... light! A HID bulb however is not like this. On startup, the ballast will convert the DC input (between 6vdc and 14vdc on a conventional car, much more limited for a Prius because there is no "cranking") to an AC signal at about 400Hz between 20kv to 30kv on startup and a resting voltage of between 80vac and 105vac. Note how I said 20kv to 30kv. The "kv" is kilovolts, or thousands of volts. Your house (in North America) runs 60Hz 110vac. So your car is pumping out 20,000vac to 30,000vac for a brief period of time. This is a huuuuuuuuuuge strain on the bulb, ballast, and ballast wiring. Luckily it only happens while turning on the bulb. See where I am getting to? When your bulb starts to go out, and you turn them on/off/on/off/on/off/on/off trying to get it lit, you are basically blasting your ballast and wiring with high stresses so much more than they should be. Things designed for high voltage startups generally can handle it for a limited time and then need a cool down period before you try again. You are eliminating the cool down and making it work as hard as possible many times in a row. So don't do it! A ballast is much more expensive than a bulb. What kind of bulbs? So now that we have determined how to tell if a bulb is dying, we need to know what to replace it with. This is not easy if you don't know what you are doing or what to look for. I hope to inform you here so you don't get ripped off. First off, the OEM for Toyota is Philips. German and very good quality. However when they have a bad batch, everyone gets a bad batch which did effect some 2006-2007 models of Prii. Other high quality to medium-high quality manufacturers include: OSRAM/Xenarc (also makes Sylvania), Koito, Panasonic, and GE. Koito is a big OEM for Toyota along with Denso (they make the ballasts, radio, nav unit, many of the ECUs, etc...). However as far as us HID people who aren't actually in the industry know, they don't have a bulb plant. It is speculated that they buy bulbs from Philips or OSRAM, but that is speculation. Also, the only bulb we have ever seen is the "Koito D2S" bulb. Generically marked and hard to determine the actual origin. It is also hard to source, so in general just stay away. GE is trying hard to enter the bulb arena, but it is generally accepted that their bulb quality is still inferior to Philips and even to OSRAM. They are the only quasi-quality manufacturer with a 9000K bulb, however it is illegal for road use in the US, Canada, and all of the EU. Panasonic also is an OEM for many vehicle manufacturers. (Nissan likes them). However their bulb division is actually Matsushita and their bulbs are stamped with an "M". They also only make D2S as far as I know. Again Matsushita has no bulb factory of their own, and again it is speculated that they buy manufacture silked Philips. The bulb structures are nearly identical, but again it is speculation as they are not marked as Philips. So really, what I am saying here is to stick with Philips. If you have a 2004-2005 Prius, you have D2R bulbs. If you have a 2006+ Prius you have D4R bulbs. The difference being the D4x bulbs are Mercury free. If you do a retrofit (highly recommended) then you can have anything, but generally D2S. Note that D2S and D4S are the standards in the industry. The "S" denotes that it is for use in projectors (_S_traight) while the "R" denotes that it is for use in _R_eflectors. The optics are different and the bulbs are not meant to be mixed and matched. You can however cut notches into the base and "make it fit", but that is ill advised. So because D2S and D4S are the industry standards, bulbs are mostly made and designed for these bulb bases and optical properties. Some are "ported" over with minimal changes, some are designed from the ground up. Also just for extra info, D4x bulbs are about 200-300 lumens less bright than D2x bulbs because there is an extra glare shield blocking and then the mercury really does improve light output which has been removed for environmental reasons. If you want your basic replacement bulb: D2R that colour shifts after 100 or so hours: 85126 or 85122WX (identical bulb, different markings) D2R that doesn't colour shift: 85126+ or 85122WX+ D2S that colour shifts after 100 or so hours: 85122 D2S that doesn't colour shift: 85122+ D4R that colour shifts: 42406 D4R that doesn't colour shift: 42406+ (rare) D4S that colour shifts: 42402 D4S that doesn't colour shift: 42402+ (rare) What makes a bulb (quick overview for terminology below) If you look at the picture below, you will see a standard Philips 85122 bulb. The base is the big black bit that actually connects to the connector. There is an inner chamber and an outer chamber of glass made of different materials. One part of the electrode travels from the top of the bulb through the twisty metal bits back to the base of the bulb. The other part of the electrode goes directly from the base of the bulb into the glass chamber and is harder to see. The salt chamber is the "bubble" in the middle of the inner glass chamber. The electrode ends in the two parts where it is pinched together before the bubble. eBay here we come! No don't do that... No... There are many more things to know about bulbs. Similar to how clothes have rip-offs that are branded the same or pretty much any electronics device by a major manufacturer that has a ripoff, so do HID bulbs. Every wonder why some standard 85122/85126 bulbs are $15/pair on eBay while others are $300/pair? Well, quality counts. Some things to keep in mind: Filament: The filament of genuine high quality bulbs are made from thoriated tungsten. A long time ago when microwaves were new technology, thoriated tungsten electrodes were introduced as an alternative to the use of pure tungsten electrodes. 1-2% of the electrodes are made up of thorium dioxide (ThO2) which makes the bulb last longer because the electrode is more robust. Remember above where the bulbs end of life comes becomes the electrode slowly corrodes away and eventually the 20-30kv spark cannot bridge the cold gap? Well the more robust the electrode, the slower it erodes, the longer the bulb lasts. Some bulbs are actually marked "LL" for Long Life like the Philips 85122LL which come standard on the Lexus LS series (like the LS430 which has one of the top 3 most coveted projectors). The LL bulbs generally contain 2% to 3% ThO2. Which make them erode even more slowly. An added benefit of ThO2 is that it has a more even heat profile and current flow which promotes a more stable arc across the salt gap. This produces a more stable and consistent light output while putting minimal stress on the salts themselves. Cheap bulbs generally are made of pure tungsten which is super cheap, and super crap. It erodes quickly, and the bulb life is short. It also stresses what little salts are in there (more on that in a bit) and the output can be "wavy" or inconsistent over temperature and/or time. In general the luminous output is also less with a tungsten filament because more of the current flowing through the filament is transferred to heat versus being used to arc the salts (making more light). Salts, the HIDs heart: Yes your HID bulb has salt in it. The salt is the heart of your bulb and is used as fuel essentially. I keep talking about the salt chamber, air gap between the cathode and anode, and the firing voltage to excite the salts. Well this is what makes the bulbs tick. When the bulb is first getting turned on, a 400Hz 25,000 volt signal is sent through the bulb. Although at least one manufacture uses 4KHz (4000Hz) and some oldschool 90's German vehicles with 1S/1R bulbs sometimes use high voltage DC (yikes!!!). The reason for the AC is because it puts the stress on the anode every time it fires and stress on the cathode every time it strikes. If you switch directions (what AC does) then the anode becomes the cathode and the cathode becomes the anode. Since the wear is different, switching back and forth makes the life longer by equally destroying itself. Anyways, that initial 25,000 volt signal jumps between the anode and the cathode in the salt chamber. This makes an electrical arc and the electrodes glow slightly blue-ish at the tips. This arc is hot. Very very hot. It makes the salts very hot. Eventually (milliseconds) the salts start to vapourize literally. The vapourized salts are then ionized by the arc between the electrodes making plasma. This plasma is super hot, super unstable, and extremely excited so it shoots photons off like nothing else making light. Along with photons it shoots of lots of bad radiated waves as well, more on that later. Once the plasma is created and the salts are vapourized, the ballasts can drop the voltage to 85vac and generally it is +/- 17vac to keep the arc going. 85vac is standard, but some run higher, some lower, and cheap ones jump around. So since the salts are the heart of your bulb, your bulb is only as good as the salts you have. Some common salts and their colours are: Sodium Iodide - White Thallium Iodide - yellow crystals that become red at 170oC Scandium Iodide - yellow powder Dysprosium Iodide - deep yellow powder Indium Iodide - deep red-brown color Mercury Iodide - Yellow (may or may not be added, but it may form due to the presence of iodide from the other salts) More rare (i.e. exotic and expensive) salts: Cerium Iodide-Yellow Neodymium Iodide - Green Holmium Iodide - yellow Erbium Iodide - Pink Thulium Iodide - Yellow Gadolinium Iodide - yellow Ytterbium Iodide - yellow Generally most bulbs are made of Scandium Iodide and Sodium Iodide. Higher temperature good quality bulbs use more Indium Iodide which is really expensive and hazardous to use (read as expensive). Every company has a closely guarded recipe of salts to make the precise colours. Cheap aftermarket crap generally use low quality salts and/or salts cut with other materials to barely allow the plasma to form and are easily diluted. All of the salts listed above are extremely expensive in high purities. When you look at the salt chamber of a Philips or high quality bulb, you will see it very yellow (or red) when new. When you look at a new cheap bulb, it will be almost clear. Almost clear means almost no salt, which means very very bad. Also the less salt in the chamber, the less salt vapour and the plasma is more unpredictable generally producing more heat and less light output. This makes these bulbs run hotter and again unevenly. When the electrode erodes, it actually starts depositing the tungsten in the salt chamber mixing with the salts. The salts themselves turn gray-ish because they are "burnt" but they are also mixed with tungsten as well. So over time with a little tungsten added, some colour shift to a different light spectrum and eventually too much tungsten decreases the luminous output. So new bulbs will first become whiter then slowly dim until there is not enough electrode left to make the air gap, or the salts are too contaminated by tungsten waste to vapourize and become plasma properly. Electrodes: We covered the chemical/material properties above with the difference between pure tungsten (bad) and a mix of ThO2 and tungsten (good). But there is also a mechanical aspect to it. Cheap bulbs sometimes have the electrodes sideways, crooked, or too short. The first two jeopardize the optical properties of the bulb and the structural integrity of the inner/outer glass chamber vacuum seal and chambers in general. Symmetrically sealed chambers can make the mechanical stress focus on the point of the glass by the electrode which is strongest versus if it is offset then the stress is still focusing on the tip of the glass but there is nothing there to hold it up. Glass Chambers: You are putting your health at risk and your projectors' chrome lining with cheap bulbs. Not only do the cheap bulbs burn hotter because of less salt, they burn more unstable. The plasma also radiates extremely intense UV rays along with other nasties. If you look at a good bulb you will see an inner chamber made of high temperature glass and an outer chamber sealed by a vacuum made of lower temperature glass but high UV blocking properties. Cheap manufacturers either use low quality outer shielding or some leave it off altogether to save costs. If you ran this bulb and stood infront of the bulb you would get a severesunburn. Similar things can happen with cracked glass chambers even on high quality bulbs. So there is the obvious health hazard, but to get to the chrome hazards, when it gets too hot the chrome will bubble. When the chrome bubbles, you get uneven spreads and hotspots at best and ignition/fire at worst. Remember you aren't dealing with grandma's bulbs. These are high voltage, high current, and extremely high output lights. Base Structure: The base structures of good high quality bulbs have large uniformly shaped rivets sturdily holding the base to bulb. The glass tubes are not overly large or fragile, The inner wire to the glass chamber has slack in it to allow for thermal expansion and contraction. Cheap bulbs have really crap rivets or sometimes none at all on some legs. The bulb base glass is sloppy which gives room for excess stress on the bottom, and in some cases the power wire is straight and taught which can snap, become overstressed, strained, or thinout with temperature variations. Identifying Crap: So to put this all together, here are some images and descriptions of bad bulbs versus good bulbs as sourced from hidplanet. The captions are below the images. "Real" denotes a real genuine Philips 85122 bulb. Fake 1 and Fake 2 denote cheap crap bulbs that claim to be 85122 bulbs but are nowhere even close. Real: Very good formation of the glass, small indentation in the center, return wire wild is encased in glass, bulb is sealed far from the glass body. Fake 1: Much taller than the real Philips, return wire weld is not encased in the glass, bulb is sealed much closer to center of bulb body. Fake 2: Sloppy formation of glass (slightly tilted and not straight), Return wire weld not enclosed in glass, bulb is sealed much closer to center of bulb body. Real: Nicely formed oval shape capsule, good size that is symmetrical in shape, thicker glass encasing diodes, white or slightly gray colored salts. Fake 1: Poorly formed capsule more square in shape, poorly formed glass that encases diodes very uneven, salts are red in color which is not correct for an 85122+. Fake 2: Oval shaped capsule that is very small and not symmetrical in shape, thin glass encasing diodes, salts are white and slightly yellow. Real: Larger perfectly symmetrical rivets, nicely tapered and formed lower glass tube, Zig-Zag Pattern of lower power wire within lower glass. Fake 1: Smaller rivets, the glass is nicely formed but the tube is overly large, lower power wire is mostly straight. Fake 2: Rivets are almost not noticeable, poorly formed lower glass tube, has Zig-Zag lower power wire. Real: Typing is made up of individual dots, matte white in color, spacing between words, letters and lines is all uniform. Fake 1: Typing still using individual dots but dots blend together, much too bright white, spacing is not uniform between letters and much too narrow between lines. Fake 2: Typing still using dots but blend together badly, much too dull white, spacing is not uniform and letters are not formed correctly Real: Small solder at the top is perfectly centered and nicely formed, protrusion on the center metal post fill most of the surface and nicely formed Fake 1: Small solder at the top is not centered and poorly formed, protrusion on the center metal post is poor formed and much too small. Fake 2: Small solder at the top is almost non-existent, protrusion on the center metal post is poorly formed and very small. Conclusion: So now you are armed with the basics (maybe slightly more than basic) of HID bulbs and the phoneys out there. Make sure to look for these features. I see bulbs on eBay right now for $15 that are the same as bulbs on sale for $300. You cannot go on price alone. You must make an informed decision. If you want to buy genuine bulbs, buy from a genuine wholesaler or retail outfit. I recommend theRetrofitSource.com for bulbs as well as the Toyota/Lexus dealership. Expect to pay between $50 to $100 per bulb. After reading through all the technology that goes into these bulbs, hopefully you will know why they cost more and are worth more than the walmart bin halogens.