Well...Read the below review. I wrote this about 10 years ago, so some info is a bit dated, and slightly incorrect, but it gives an o.k. account of the lights available at that time::
The advent of small, high powered lights utilizing 3 volt lithium cells has brought the power of traditional heavy lights into the palm of your hand. The most popular sizes of these lights use 2 lithium cells (DL-123 or equivelant) connected in series to produce 6 volts (1300MAH). This battery configuration combined with a high pressure halogen/Xenon bulb equates to a high output light in a size efficient package.
There are many ways to measure light output, though the two most common measurements are candlepower and lumens. Candlepower measures the light's output at its brightest point in a focused beam. Candlepower takes into account the bulb brightness as well as the efficiency of the reflector assembly. The lumen is the measurement of the total output of the light, without regard for the reflector assembly, thus making the lumen a measurement soley based on the lamp output. Other factors which may influence light output ratings are the human eye and the color temperature of the lighting device. The perception of the light's brightness will be different for all people, because each person sees the light a bit differently. This is quantified, somewhat, by the color temperature of the light, as higher color temperatures produce a "whiter" looking light.
The 3 volt cells used by these lights are extraordinary power sources. The DL-123A (or equivelant) cells feature 1300MAH capacity, with a maximum discharge current of 1500MAH (to further illustrate the power of these cells, they are capable of producing 3500MAH of current at one volt when shorted). They also have an internal thermal switch, which will shut the cell down if the peak operating temperature becomes to high (one of the reasons why Surefire recommends Duracell batteries is because Duracell cells have a higher thermal cut-off point). Because of their lithium composition, these cells can also operate in extreme conditions, with a an operating range between -40 degrees Celsius to +60 degrees Celsius. Average shelf life is ten years, with only 1% of capacity lost per year..
There are five different manufacturers making flashlights that use 2 lithium cells as a power source: The Surefire 6P, the Streamlight Scorpion, The TACM (model 00000), the Underwater Kinetcs 2L, and the A.S.P Tac-lite. All will be examined, except the Tac-lite, as I do not own one of those.
SUREFIRE 6P: Perhaps the oldest of the group, the 6P uses an aircraft-grade aluminum body, O-ring seals at the tail cap and head, and also uses a rubber tailcap for momentary operation. The tail cap can be rotated for continous light usage. The body and tailcap also feature light checkering to produce a non-slip grip. The bulb assembly consists of an aluminum reflector, two stacked springs, and the actual lamp, which is cemented into place. The entire package ensures a focused beam without any flaws or spots. Operation is as simple as pressing the tail cap to actuate the light, though the tail cap should be backed-off slightly to prevent accidental lamp operation, which could lead to dead batteries and a burned-out lamp. There's not much to improve with a 6P, though the lamp modules tend to be fragile, and the lamp filament may break if the light is dropped. Also, lamp life averages about 15-20 hours in my experience, which isn't as high as the other lights in the test. Battery life averages 45 minutes to one hour with a P60 lamp module, which is rated at 65 lumens. Surefire also offers a high output lamp module, the P61, which is rated at 125 lumens. Battery life with a P61 lamp averages about 15-25 minutes of continous usage, though heat build-up at the head assembly is a significant concern if the light was used continously. Average street price for a 6P is $55.00-$65.00, with lamp modules averaging $18-$20.00.
STREAMLIGHT SCORPION: Streamlight is best known for the SL series of full size duty flashlights. A relative newcomer to the Lithium light scene is Streamlight's Scorpion model. The light is a bit longer then a 6P, though the body is narrower. Construction consists of an aluminum head and body, with the body surrounded by a rubber skin. There is no tailcap on a Scorpion, but the butt section of the light has an integrated switch which allows momentary or constant operation with thumb pressure. The light uses a bi-pin high pressure Xenon bulb, with a reflector built into the head assembly. The head assembly, which is sealed by an O-ring, also houses a spare bulb, which is included with the light. The reflector/head assembly allows the Scorpion to have partial focus capabilities. The lamp is shock resistant due to Streamlight's use of a small silicon O-ring supporting the bulb. Overall performance with the Scorpion is excellent, with a very bright beam that does not exhibit any dark spots or distortions. The beam shape consists of a large primary beam with a larger corona, making the Scorpion ideal for close quarter illumination. It isn't as bright as a 6P for longer range usage but easily equals the 6P's flood capabilities. Lamp life is approximately 30 or so hours (about 4 battery changes), with battery life averaging 50-60 minutes. Streamlight rates the light at 6,500 candlepower. Streetprice for a Scorpion is $35-$45.00, with lamp prices averaging $5-$6.00.
TACM: Originally, the TACM was designed around a weapons-mount system in which the light is clamped into a housing with the housing attached to the floor plate of the weapon's magazine. This limits the TACM's light outside of the weapon's mount because the switch assembly is awkward. Eventhough it uses the familiar tailcap switch, the TACM's tailcap is a one piece unit that needs constant adjustment to keep proper tension for thumb pressure usage (note that TACM has released a re-engineered tail cap that should cure this problem). The light uses a Delrin outer shell encasing an alumninum body. Delrin is a space age thermoplastic which is incredbly tough yet very lightweight. Both the head assembly and tail cap use O-rings to keep moisture out of the light. The bulb assembly is very similar to the 6P's, with dual springs, an aluminum reflector, and a bulb which is cemented into place. TACM rates the light at 105 Lumens, and it seems that bright, as the TACM easily outshined the other lights when used to illuminate distant objects. This comes with a tradeoff, however, as the TACM's flood capabilities were limited. Both the Scorpion and 6P had brighter beams on closer objects then the TACM. One problem I have had with the TACM concerns the lens. It seems to be very vulnerable to the lamp's heat output. Because of this, I have warped two lenses, and the head assembly has to be returned to TACM for replacement. Street price for a TACM is $65.00-$80.00, with lamp assemblies costing about $20.00.
UKE 2L: Underwater Kinetcs primarily manufactures diving lights. The 2L is no exception, as it's heritage clearly shows. It features a one piece plastic body, and a transluscent rotating head assembly which also acts as the switch. The whole unit is sealed by double O-rings at the head/body juncture. The lamp assembly is similar to the 6P and TACM, as it utlizes a plastic reflector assembly with a small bulb cemented to it. Operation is as simple as twisting the head. There is only on/off operation, with no momentary function. When on, the head assembly glows, though it's not a usable amount of light, which is a drawback, because the 2L has a very narrow beam, with virtually no flood pattern characteristics. Even at long distances, the light pattern is small, but tightly focused. Run time is the longest of the lights compared, averaging 5 hours. Though not well known, the 2L has developed a cult following, mainly due to its low price (about $20.00) and excellent durability and runtime.
CONCLUSION: Which light is best? That's tough to answer as they all have excellent performance and features. For overall value, performance, and quality, I would choose the Scorpion. It has excellent beam quality, superb construction, and features a spare bulb, which can be costly with the other lights. I also feel it has a superior switch, allowing more varied uses for the light in a variety of situations.
2003 UPDATE for the questions in the initial thread:
--The TL-2 uses the same bulb as the Scorpion, with similar beam characteristics.
--The Peli. M-6 is a compromise between the long throw of a TACM or Scorpion and the flood capabilities of a 6P. Beam has some minor artifacts, esp. when defocused.
--E series is typical SF, with a nice hot round beam, but total output isn't equal to the others, but the beam quality makes up for that.
Somewhat generic overview. It's tough to try and write a comparison when the item being compared is measured best by the eye's of the individual user...
--dan
