There are several important terms to be familiar with when buying projector replacement lamps, especially the distinction between original and compatible lamps. Below are definitions along with some advice on what to look for before you buy. Even if you choose not to read what follows, our bottom line advice is to call the on-line store you're considering buying from to confirm that there is a lamp warranty. If a lamp is going to prematurely fail, it will probably do so in the first hours of use. Even a 60-day warranty is valuable as long as it is included in the price of the lamp.

Lamp Module - Seems obvious, but there can be confusion so we'll start here. Projector illumination comes from a light source that is mounted in a "cage" or "housing" (see diagram below). The light source is technically called the "lamp" but can also be called the "bulb". Electrical current is supplied to the lamp by "connectors" that are also mounted on the cage. The entire assembly, the lamp (or bulb) plus the cage (or housing) and the connectors, is called the lamp module. Most online stores sell the module . . even if they call it a "lamp" for short. Projector manufacturers assume that when it comes time for a replacement, customers will replace the entire lamp module (not just the lamp or bulb) and that is the procedure they will cover in the projector user's manual. Before you buy, make sure you know what your getting - the entire lamp module or just the bare lamp (bulb).

Original Lamps or OEM Lamps - Some online stores will use the term "original lamp" or "OEM lamp". What does this mean? OEM is short for original equipment manufacturer. Epson, Canon, Infocus, Sanyo, etc. These are the companies that make the projectors. They also "manufacture" the lamp module that comes with the new projector. What they actually do is assemble the lamp module from the cage (or housing) that they make and the lamp (or bulb) made by a lamp manufacturer like Osram Sylvania, Philips or Ushio. So when you buy a lamp module that is designated "original" or "OEM" that should mean that the seller is getting the lamp module either from the company that made the projector or from another distributor who gets the lamp modules from the company that made the projector.

PRO: When your objective is to replace the old lamp with one that is in all respects identical and one that will give the identical performance as the original, this is your safest purchase. There should be a 60 to 90 day warranty that comes with the purchase of these lamps.

CON: original lamps are usually the most expensive - at least 10% - 20% more than other options.

Compatible Lamps - When you see the term "compatible" it means the lamp module has been manufactured by someone other than the manufacturer of your projector. The lamp (or bulb) in the module may be manufactured by yet another company (probably not Osram, Philips, Ushio or other lamp manufacturers who hold patents on this type of lamp). Compatible lamp modules are often supplied in brown boxes with no branding, no manufacturer information and no mercury or recycling markings. There may or may not be a warranty. The levels of product testing and quality control during manufacturing are unknown to the buyer. A study of compatible lamps, funded by Philips, found that ANSI lumen values averaged 32% lower (than Philips lamps) in compatible lamps. However, compatible lamp modules may provide good value. You can expect the lamp module to fit into your projector exactly like the original. Even if the lamp optics are not identical to the original, in most cases you will have a projector that performs well even if it does not have the same lumen output of the original. What you won't know is whether the performance will drop off faster than the original and therefore won't give you the same number of hours of top performance as the original lamp.

PRO: When your objective is to replace the old lamp with the least expensive lamp module option, compatible is a good choice. You'll save at least 20% compared to buying an original. Compatibles may be the right choice especially in a situation where you know you will be buying a new projector before you would normally have to replace the lamp.

CON: Unknown lumen output and long term performance.

Branded Compatible Lamps - Think ScanDisk memory cards you may buy for your digital camera – not the original that came with your camera, but a trusted, high performance product that is equivalent to the equipment manufacturer's original. And it has been branded. The same concept applies to some projection replacement lamps. What makes them different than simply "compatible" other than the fact they have a brand name? The cage (or housing) has been re-engineered to be as good or better than the original (there have been recalls of projectors because of faulty original lamp modules). The lamp (or bulb) is manufactured by one of the major manufacturers like Osram Sylvania, Philips or Ushio. In addition, all branded compatible lamp modules go through a series of quality checks that in most cases are very similar to the quality control applied to the original lamp modules. The quality checks include: optical performance, ignition, voltage, connection integrity and runtime. The company manufacturing the "branded compatible lamp" is usually in compliance with ISO 9001 standards. There are currently at least two branded compatible lamps being sold: APOG Lamps and Diamond Lamps.

PRO: You'll get original lamp module performance at a slightly lower price - about 10% cheaper than the original.

CON: Remember the adage, "you can't get fired for buying IBM"? If you're buying for a boss with that mentality, then stick with the original, OEM lamps.

Bare Lamp (Bulb) Only Replacement - Some online stores sell replacement bare lamps or bulbs without the rest of the module. You get only the lamp, not the housing or connectors. You probably won't know who manufactured the lamp, but you can assume it's not one of the premium manufacturers like Philips or Osram Sylvania. It's up to you to get this new lamp into the old housing. Once you remove your existing lamp module from your projector and then, normally with a small screw driver, you disconnect the wire connectors and carefully remove the old bare lamp from the cage or housing. Then, just as carefully, replace the new bare lamp and make all the reconnections. What you end up with is a new lamp (bulb) in your original housing.

Why go to all this trouble? You save money - up to 50% less compared to the original lamp module price. It is clear the projector manufacturers never intended for the projector owner to disassemble the lamp modules. They don't make it easy. But it can be done. Some stores provide detailed instructions that come with the bare bulb. A couple cautions: Try to avoid breaking the old lamp when you're removing it. The lamp contains mercury which is toxic (you won't die, but the authorities don't want these lamps in the landfill so that tells you something). It the lamp does break, make sure no shards are left in the housing. Finally, the optical performance of the projector is dependent upon a precision mounted lamp. Before you remove the old lamp, carefully note how it is mounted and try to get the replacement re-mounted in exactly the same position.

PRO: You'll save money.

CON: You're on your own.