a breakthrough for independent living and emergency preparedness part 2: LED technology essentials
By Tim Thorstenson
Issue #128 • March/April, 2011
In part 1 of Light Emitting Diodes (LEDs), (Issue #127, Jan/Feb, 2011), we examined the basics of the technology. But when we get to actual LED-based products, there are critical details that vary from one kind of light to the next. This time we will consider products which include: flashlights, headlamps, portable lanterns, work lights, and bulbs and fixtures for the home or cabin.
LED performance is still improving rapidly and this makes it a challenge to provide information that won't become obsolete down the road. Because of this, we'll avoid detailed reviews of specific products. I will mention some to illustrate important principles, but the principles themselves will be the focus because they will remain useful over time. I've listed some sources for product details and reviews at the end of the article.
"Flamethrowers" come in a range of sizes and shapes. Compared to the "compact" and "micro" LED options, they are a bit bulky. But next to the 2-D-cell incandescent flashlight at right, they are quite reasonably sized.
The newest LEDs make it into flashlights pretty quickly. Considering that an incandescent 2-D-cell flashlight will produce about 20 lumens from fresh batteries, these LED options are nothing short of amazing: a compact light can produce 150 lumens (or more) for an hour or better from a pair of AA batteries. Many of these lights can be turned down to lower outputs and this can stretch the runtimes into tens or even hundreds of hours while providing enough light for routine tasks or emergencies. We do need to be aware of stuff that is of poor quality or which uses dated LEDs. But even if we eliminate the "junk," we are left with an overwhelming number of choices, so it can be a real challenge to find the best lights for your needs.
A "compact" flashlight can be practical for routine on-person carry. And the 200 plus lumens now available from LEDs can really light up the yard for safety and security.
It is helpful to first put LED flashlights into some rough categories which include store brands, "gold standard" name brands, and better quality imports. Store brands include familiar names like Coleman, Duracell, Energizer, Ray-o-Vac, and Remington Arms. Some of these lights use more recent LEDs like the Cree XR-E, but they may come from the less efficient "bins." Store brands are also comparatively inexpensive and readily available. Some of these companies sell a range of products, so check the package for information on runtimes, lumen outputs, and the type of LED being used. At the other extreme, "gold standard" name brands offer rock solid products that are built like tanks and are made in the US. These options are generally more expensive but, as the old adage goes, this is a case where you do get what you pay for. The "gold standard" category includes well-known companies like Surefire and Streamlight, but there are also some small US manufacturers who deserve inclusion. Their names may not be as familiar, but their products are definitely "gold standard" and they are often quicker to incorporate the newest LEDs.
An excellent example of a small "gold standard" company is Malkoff Devices, which already has products with the new XP-G LED. Malkoff makes some complete flashlights, but the company also offers "drop-in" modules to upgrade Surefire and Maglight products. Back in the "incandescent days," everyone from police officers to armed citizens to a few backwoodsmen fell in love with Surefire's famous incandescent "6P" tactical flashlight because it put 65 lumens into a package roughly the size of a hot dog. But Malkoff's XP-G drop-in will provide 260 lumens and a much longer battery life from the same package.
The drop-in approach is clearly useful for the person who already owns compatible flashlights, but it can also be a good choice for those who are starting from scratch. To illustrate why, consider the compact tactical flashlight produced by a small US manufacturer called Elzetta Designs. The durability of this light is amazing and the price is comparable to many of the big-name gold standard products. But it still isn't cheap and it could really tick a guy off to buy a gem like that and then have it bested by future lights with newer LEDs. Elzetta's light uses Malkoff's drop-ins, so it could be upgraded down the road to keep up with LED advances for less than the cost of a better quality Chinese import. The same flexibility applies if you are considering one of Surefire's compact tactical lights or if you like the solid bulk of a good old-fashioned Maglight. But check on compatibility with specific flashlight models before trying to marry them to a drop-in. Note that there are other sources of LED upgrade products, but I use Malkoff's as the example because they are US-made, they are by far the best quality I have seen, and they pay proper attention to the important issue of heat management.
Between the extremes of "store brand" and "gold standard" there are a number of companies that fit in the "better quality import" category. The Chinese origin of these products is an understandable objection for some, but these lights do have their place. The prices can be affordable compared to the "gold standard" products, but the quality can be head and shoulders above the "store brands" (which are usually made in China, too). These companies are quick to incorporate the newest LEDs and they offer features like adjustable brightness levels and flexible battery options that can be very useful in some settings. Examples in this category include DereeLight, EagleTac, Fenix, NiteCore, O-Light, and WolfEyes, but this list is limited to the ones that I have had a chance to examine personally. A Georgia-based company called 4Sevens has been in business for several years selling some of these brands, but they have also started their own product lines and the company has shown a knack for sensible designs. Their products are still made in China, but design, quality control, and warranty service are handled in the US by 4Sevens.
In addition to the "better quality" imports, there are also some brands that suffer from poor or inconsistent quality. An additional caution is that some of the better Chinese manufacturers suffer from inferior Chinese counterfeiting! To separate the wheat from the chaff in this category, the "general information" resources listed at the end of the article will help. Some of these lights can be ordered direct from China through bargain websites and outlets like eBay, but I'd strongly suggest using a reputable, US-based vendor. Good vendors will allow you to avoid counterfeits, they can assist with product selection, many of them will provide warranty support, shipping is vastly quicker, the prices are often not that different, and, at least a slice of the pie will stay at home.
With the newest LEDs, even "micro" flashlights like these examples from 4Sevens can combine impressive outputs with decent battery runtimes. A pen (top) along with AA and AAA batteries (bottom) provide size reference.
How big and how bright?
It is also useful to put the flashlights into rough categories of "compact," "micro," and what I like to call "flamethrowers."
The "compact" alternatives are the most abundant and the best all-around choice for most general purpose uses. These mostly use "single-die" LEDs and range from the size of a 20 gauge shotgun shell to roughly that of a bratwurst. Malkoff and a few of the imports are already offering products with the new XP-G LED and this can provide either a noticeable increase in brightness or a significant increase in battery life, depending on how the maker chooses to power the LED. Compacts often use either one or two standard AA batteries or one or two disposable lithium "CR123A" batteries. Typical maximum light outputs range from perhaps 50 or 60 lumens to 300 lumens. In addition, it is possible to squeeze upwards of 460 lumens out of the new XP-G LED, though most compacts use a lower maximum to maintain longer runtimes (and, especially with the smaller models, to avoid heat problems). A multi-die LED (or a Luminus "PhlatLED") can also be built into a larger compact and this can allow for a brighter output.
As the name implies, "micro" flashlights are smaller and they generally use one or two AAA batteries. With the latest LEDs, even these puny batteries can allow for impressive lumen outputs. For instance, the one-battery "Preon" from 4Sevens will produce about 70 lumens and the two-battery version will emit around 160 lumens. Both will run for 45 minutes on high and longer at lower settings. Micro lights are great for places like the shirt pocket where you need something that is as small and lightweight as possible, but they do also have some unavoidable drawbacks. Their small reflectors yield fairly broad beams that are great for close work but which have limited long-range utility. Also, they typically have rather thin bodies to minimize weight and this makes them less durable than a good compact. Since AA batteries have a much higher energy capacity than AAA, even though most stores sell both for the same price, I personally lean toward the larger "compact" lights for general purpose uses.
At the other extreme, we have the "flamethrowers." These use multi-die LEDs, Luminus PhlatLEDs or an assembly of three or more single-die LEDs to produce much higher outputs than the compacts500 to 900 lumens and more. The flamethrowers are still bigger than the compacts, but most are still smaller and lighter than a good 2-D-cell metal flashlight and, in spite of their outputs, many of them will run for an hour or more on a set of batteries. The flamethrowers are more than some folks will need, but they can be incredibly handy for certain applications. As with the smaller options, many provide adjustable brightness, so the same light that can be used for finding a cow or scaring off an intruder can also be used for rummaging in the toolbox without blinding you for the rest of the night. Malkoff Devices and the other import companies mentioned all offer one or more flamethrowers, but for technical reasons, many of them provide a relatively broad beam focus, so their effective range may not be as great as their lumen ratings can imply. For general use, a broader beam is usually better, but if you want maximum range for things like security, checking cattle, or spotting coyotes, use particular care with product selection.
These EagleTac compacts use the new XP-G LED and they illustrate typical power options: The one at left uses two AA batteries. The other two take a pair of CR123A disposables as well as lithium ion rechargeables, but the fatter light at right will hold a bigger rechargeable and its larger reflector yields a tighter and brighter beam.
For long-range needs, products like the Dereelight "DBS" and Streamlight's "Supertac" use goose-egg-sized reflectors to squeeze the more humble outputs of single-die LEDs into amazingly tight beams. The surprising result is that these lower-lumen options can greatly outreach many of the flamethrowers in terms of effective range. These choices are also much smaller and lighter than most flamethrowers, so they can be more convenient for weapon mounting or carrying in a belt holster. Such products are not the best choice for general purpose use because they can produce tunnel vision and blinding glare at close range, but they can be extremely handy for tasks like security and nighttime varmint hunting (where legal, of course). The Malkoff drop-ins for Maglight flashlights will also produce a tight beam. This is a bulkier option, but it also allows adjustable focus.
There are also "Super-Flamethrowers" that have raw LED outputs of 1400 to 2000+ lumens. This can be done by putting two or three multi-die LEDs (or six or seven single-die LEDs) into a single flashlight head. One of the better-regarded Chinese companies (OLight) has already put the "SST-90 PhlatLED" LED into a larger (and expensive) flashlight that provides an LED output of around 2200 lumens. But note that there is a competing technology called "high intensity discharge" (or HID) that can be a viable alternative in cases where huge amounts of light are needed at high efficiency.
There are two ways of rating lumen outputone is the raw emission of the LED and the other is the actual output of the flashlight itself. Most store brands and many of the imports cite LED lumens while the gold standard companies and a few imports will actually provide true flashlight (or "out the front") lumens. Because of unavoidable efficiency and optical losses, actual flashlight output will typically be at least 20% to 30% lower than the "LED lumens." In other words, a flashlight with an actual output of 200 lumens will likely be at least as bright as a product which quotes an LED output of 250 lumens.
Do not make too big of a deal out of brightness. The human eye does not respond to light in a "linear" fashion, so a flashlight that puts out twice the lumens will not appear "twice as bright." A brightness difference of 20% will not prove that significant in most practical settings.
Malkoff Devices' LED "drop-in" modules can provide top-end LED performance from existing SureFire (left) and Maglight (center) flashlights. They are also used in the rugged tactical flashlight made by Elzetta Designs (right).
You also need to consider things like beam pattern, adjustable brightness options, how brightness is adjusted, and the type of batteries used. With these variables, there is no "best" choice because that depends on individual needs. There is also the availability of useful accessories (colored filters, pocket clips, suitable holsters, etc.) that you may or may not need.
For example, a flashlight with multiple brightness settings is great for many uses, but it can be a negative when it comes to security or self-defense. One common design allows the user to toggle through the settings by tapping the tailcap switch and it is very easy to accidentally tap yourself into a candlelight output at the precise moment when maximum brightness is urgently needed. But others provide two or more brightness levels by rotating either the head of the flashlight or an adjustment ring. This may be a better choice if you want a defensive light that also offers brightness adjustment (just remember to leave the thing on the right setting).
It's important to mention battery options. Many "store brands" use AA batteries while the "gold standard" products more frequently use a small but potent lithium battery called the "CR123A." The imports frequently offer their compacts in your choice of the two formats. If you are familiar with the outrageous price of CR123A lithium batteries, you may have a very low opinion of buying a flashlight that uses them. But these batteries can be ordered at quite reasonable prices and they do offer some advantages, so it's prudent to touch on a few pros and cons concerning battery choice.
First, it should be understood that AA-format flashlights will work best with rechargeable "Nickel Metal Hydride" (NiMH) batteries. Alkaline AAs will work, but shorter runtimes (and probably a fading output) should be expected, especially at the higher brightness settings. NiMH is a far better chemistry than the old "ni-cads" (Nickel Cadmium) and the "precharged" variety will hold its charge for several months in storage. But if you prefer to avoid rechargeables, the CR123A format may be worth a look. A light that uses CR123A batteries will typically provide both a little longer runtime and a little more brightness than an equivalent AA-format product because of the extremely high energy capacity of lithium batteries. In addition, disposable lithium batteries boast a very long shelf life (10 years or so), a tolerance for high temperatures in storage (but with a shortened shelf life), and an ability to maintain good performance in the extreme cold (down to -40 F). Some (but not all) CR123A format lights can also use lithium-ion rechargable batteries and this chemistry is superior to NiMH in certain respects.
If you want the benefits of disposable lithium, you can find them in the AA batteries like Energizer's "Ultimate Lithium" and store prices for these are often more reasonable due to their popularity in electronic devices. In addition, NiMH rechargeables are also readily available from the local store whereas lithium-ion usually has to be ordered. As a result, the AA format can be a flexible and convenient choice: a few lithium AAs can be salted away in the emergency kit, NiMH rechargeables can be used for routine purposes, and alkaline AAs are available at any gas station or grocery store.
Elzetta Designs' mounts for long guns are particularly flexible because they come with spacers that will fit a wide range of flashlights. But care should be used in selecting the right light for this demanding environment.
A couple of safety warnings: if you use disposable lithium batteries, I would suggest sticking with good name brands (Duracell, Energizer, Panasonic, Ray-O-Vac, Sanyo, etc.) and buying them from a reputable vendor to avoid counterfeits. Bargain lithium batteries have been known to explode on occasion but the name brands include internal protections. Use care, too, with lithium-ion rechargeables. In spite of their similar names, lithium disposables and lithium-ion rechargeables are very different critters and the disposables should never be recharged. Lithium-ion rechargeables have been known to burst when being recharged and can even start fires, so it is important to stick with good quality batteries and chargers and follow handling instructions carefully. In addition, there are several different battery sizes and formulations that fall under the "lithium-ion rechargeable" umbrella. These can vary in voltage and the compatibility between different flashlights, chargers, and batteries is not uniform. The wrong combination can lead to poor performance, product damage, or even fires and injuries. Some import products are only intended for use with certain rechargeables and not with CR123A disposables. With the gold standard products, the reverse is often truedisposables are the only recommended choice and certain rechargeables can burn them out by supplying too high of a voltage. For safetyand to avoid the headache of needing multiple battery formatsplease investigate lithium-ion rechargeables carefully before adopting them.
We should specifically mention this application because of its unique demands. For handguns, there are dedicated weapon lights that mount on the accessory rails now common to many pistols. Some of these can also be fitted to rail-less guns (like standard 1911s) by using an adapter kit. A given manufacturer will typically offer a range of such lights to fit different needs. For instance, Streamlight's "TLR-1" is suitable for full-sized pistols and emits an actual 120 lumens. Their TLR-2 uses an identical light source but adds a red aiming laser. For smaller handguns, they also have the very compact and lightweight "TLR-3" which produces 90 lumens from a single, smaller battery. Similar choices can be had from some other "gold standard" companies too, but the big caution in all cases is that the pistol makers definitely don't have their act together on a standardized accessory rail. Regardless of the brand of light you are considering, check your gun(s) with the light maker's compatibility information.
When we get to long guns, such lights can also be used if the gun has an appropriate rail. But you can also use standard tubular-bodied flashlights. Companies like Streamlight and SureFire sell brackets and remote switches for certain models of their lights and there are also mounts available that will allow you to use your own choice of flashlights. For instance, Elzetta Designs makes some excellent mounts that can be used with their own super-tough flashlight. But Elzetta's mounts can also be bought separately and they will accommodate a wide range of other flashlights. This is handy, but it also gets us to the relevant warning. Lights sold by gold standard companies as suitable for weapon mounting are designed and tested to handle the recoil. But this may not be the case with generic, off-the-shelf alternatives. In addition to the LED, a flashlight also has electrical, electronic, and mechanical components and weaknesses in any of these could lead to failure. In this application, the gold standard products may be particularly worthy of the investment.
The durability and efficiency of LEDs make them the perfect choice for weapon lights like the Streamlight products shown here. Even a tiny, lightweight unit like the TLR-3 (top) can produce a very respectable output.
Much of what was said about flashlights also applies to headlamps, but there are a couple of special considerations. Heat sinking is a challenge, so you won't find many with multi-hundred lumen outputs, and there are fewer options in this category but there are still some good choices:
In the "gold standard" category, SureFire has recently released a very bright but very expensive model called the Saint. Streamlight has had an array of headlamps for a long time and now offers several LED models. There are also some companies (such as Black Diamond, Petzl, and Princeton Tec) that are specifically known for their high quality (and relatively expensive) headlamps. As with flashlights, the biggest and best-known companies are often a little slower at incorporating the latest and most efficient LEDs. The import companies have not really jumped into this market with both feet, but Fenix has models that use one, two, or four AA batteries. The four-battery model uses a little electronic trick to allow a maximum LED output of around 225 lumens: after a few minutes, it will drop down to 120 lumens to prevent overheating of the LED. "ZebraLight" is another quality import brand and they have several unique and flexible products. Note that these provide a broad and uniform flood of light which is great for close work but is very ineffective at longer range. 4Sevens offers a headband and a slip-on periscope contraption for their compact "Quark" lights and it can convert these into headlamps or pocket work lamps.
There are also some "store brand" products of decent quality and efficiency. For example, there is a "Remington Arms" branded product that uses four AA batteries and cites an output of 150 lumens (likely a raw LED output). The unit is bright and well built and it offers two brightness settings, a diffuser to spread the light for closer work, red LEDs for low light applications, and a "blood tracker" setting to aid in tracking wounded animals. Energizer, Coleman, and Ray-O-Vac branded products are also available with newer LEDs. As with flashlights, some store brands offer a range of quality options. Again, reading the packages will often reveal the ones that use more efficient LEDs like the Cree XR-E.
There are dozens of LED-based lanterns, but many of these use older and less efficient LEDs. These options are not always a bad choice. If a person wants several inexpensive lanterns to have on hand for power failures or an occasional campout, some of these can be an affordable alternative that will provide adequate brightness and a much longer runtime than an incandescent equivalent. But when it comes to newer LEDs, the choices are more limited. The gold standard brands have never been in the area lantern market and the better-quality import brands have not offered anything that I am aware of. However, there are some store brand options worthy of note. Remington Arms has a 4 D-cell model that cites an output of 350 lumens. Ray-O-Vac offers a somewhat more compact alternative that uses 3 D-cells and also claims 350 lumens. Coleman has several lanterns that use efficient LEDs and they are available in a range of sizes and outputs.
In this product category, we also need to consider fluorescents. The efficiency of better-quality "compact fluorescent" bulbs can rival that of all but the newest LEDs, but they may not perform well in camp lanterns. In addition, LEDs eliminate the problem of fragile tubes and allow for more flexibility with brightness adjustment. If you have some fluorescent lanterns that you are happy with, it may be prudent to wait for the newest LEDs (like the Cree XP-G) to make their way into this product category.
Some store brand products can be had with quite efficient LEDs. Shown here are a lantern and headlamp sold under the "Remington Arms" brand name.
Another option here is using handheld LED flashlights with diffusers to spread the light. Several companies offer attachments for their lights and it is also pretty easy to homebrew something with a sheet or tube of translucent plastic material. This approach can be especially handy in emergencies or where space is limited, but be careful of heat buildup. At maximum brightness, most flashlights run the LED at a pretty high power level and a flashlight body is not the greatest heat sink for extended operation, so damage to the LED is possible. An adjustable flashlight with lower brightness settings is a good idea for applications like this.
Area lighting is also a category where the build-it-yourself option could be rather appealing. For about $50-$70 you can get the parts needed to make a light source capable of 500 to 1,000 lumens (depending on your choice of components). The basic setup can be built into a housing that suits your fancy and operated from a 12-volt source while using roughly 8 to 12 watts of power at maximum brightness.
Portable work lights
Every reader can think of many uses for a decent work light or trouble light that can be operated from a 12-volt source (such as the car or a small battery). With the best of the LEDs, it would be pretty easy to design something that could belt out several hundred lumens while using only a few watts of power. Given the fact that many of the "consumer" products (such as the trouble lights which use large arrays of "pin type" LEDs) can be rather disappointing, building is also an attractive option here. The same light-making setup just mentioned could also be built into a package that includes suitable magnets, clamps, or hooks for mounting. Bare LEDs generally emit a broad flood of light, but a tighter beam may be desirable in a work light. If so, inexpensive focusing lenses are available to shape the beam to a pattern that meets your needs.
If we look to "commercial grade" products, we can find some very impressive options. A well-stocked example is "Larsen Electronics" (also known as "MagnaLight"). This US-based company has been in business for many years making and selling incandescent spotlights and other 12-volt lighting products and they now have an assortment of commercial quality LED work lights. Outputs of up to several thousand lumens are available (accomplished by ganging together multiple LEDs), but the drawback is that such products must be sold with a pretty high price tag because of the component costs. Extremely bright LED-based work lights have caught the interest of those in the trucking, mining, and heavy equipment fields and LED prices are expected to go down over time, so commercial quality options will hopefully become more available and less expensive.
One problem with new technology is that it can cause people to put on blinders and conclude that the new thing is always the best thing. This assumption can be especially dangerous when we get to lights for the cabin and home. For instance, a person working out of a vehicle could get quite a bit of light for a comparatively small investment by using some halogen incandescent "tractor" lights. Because of the poor efficiency, these use a lot of power and can kill a car or truck battery pretty quickly if you don't care to leave the vehicle running. But adding a good deep cycle battery to the setup could still prove cheaper than buying or building a multi-thousand lumen LED light.
If you need to light up a large area in a more efficient fashion, High Intensity Discharge (HID) is also an option to consider. This is basically the same technology used in everything from stadium and warehouse lights to portable light towers to the very irritating headlights found in some fancy cars. HID can provide an efficiency of around 100 lumens per watt and outputs are really limited only by the size of battery you are willing to drag around. 1,000 to 3,000+ lumens can be had from units sized like overgrown flashlights and bulky lanterns and even more is available from 12-volt corded products which are available in both spot and flood configurations. A potential drawback of HID is that most designs require a few seconds of warm-up time in order to hit full brightness and it is not the best choice for tasks that call for short bursts of usage and frequent on-off cycles. This can make HID a nuisance for flashlight use, but it is usually less of a problem with work lights. HID typically provides little or no brightness adjustment and it requires fairly expensive bulbs which will probably never wear out on most users, but could possibly break. Drawbacks aside, it can be a viable choice for some needs. Various HID products can be had from MagnaLight and other vendors.
Building it yourself can be especially attractive when it comes to work lights. It allows the use of the best available LEDs and you can design a light that actually fits your needs.
Fixtures and bulbs for the cabin or home
We must not only compare different LED options to each other, we must also compare the LEDs to the other options when it comes to cabin and home use. Most notably, limitations like space, weight, and durability are usually not that critical and this allows for other alternatives like fluorescent and metal halide. In addition, we need to be extremely careful with the term "efficiency." As we saw in Part 1, the raw "lumens per watt" rating of a given LED is one thing, but the final useful efficiency of a bulb or fixture is another. Some loss here is simply unavoidable, but the difference between a good design and a sloppy one can be very dramatic.
In this respect, it is also important to be careful of "adjusted" efficiencies or creative ways of stating efficiency. Very importantly, this applies to other technologies as well as to LEDs. For instance, I've seen outdoor CFL (compact fluorescent) fixtures with efficiencies that have been "adjusted" based on a study which showed that cool white light sources will appear brighter than their raw lumen values would suggest. This is not exactly helpful because meaningful product comparisons become impossible. In a similar vein, one should be careful of bulb suppliers that simply parrot the ideal outputs and efficiencies of the LEDs themselves rather than providing realistic numbers for the actual final products. Another thing to watch out for is the "CRI" or "Color Rendering Index." This number has its uses, but it applies to color perception and not to efficiency. Finally, a statement that a certain LED bulb "is equivalent to" a certain incandescent bulb does not mean that its lumen output will be comparable.
With these facts in mind, it is useful to ask: what is reasonable to expect in terms of LED bulb and fixture efficiency? We saw in our first visit that a very well designed bulb or fixture can provide an efficiency that is about 75% of the efficiency of the LED itself (this allows for optical losses, power used by the electronics, and efficiency losses which result from running the LEDs at higher than ideal temperatures). Applying this 75% factor to the efficiencies of the best available LEDs can give a reasonable, though perhaps optimistic, reference point. Recently, Cree released neutral and warm white versions of their new XP-G LEDs, so we can use these to establish a "best case scenario" for the top LEDs that are commercially available at this moment. In cool white, best low power LED efficiency is around 132 lumens per watt and 75% of this gives us a potential bulb/fixture efficiency of around 100 lumens per watt. Cree has demonstrated this level of performance in some prototype street lights and it suggests that 75% is not an unreasonable number to use. Neutral white XP-Gs come in at 124 lumens per watt, so we could expect bulb/fixture performance of around 90 lumens per watt. Finally, warm white XP-Gs can provide 102 lumens per watt, which leads to a possible bulb/fixture capability of 77 lumens per watt. It is important to understand that these estimates are based on best-bin LEDs being run at low power. Lower bin LEDs or higher power operation will lead to lower efficiencies. (For reference, recall from Part 1 that standard incandescent bulbs have an efficiency of around 13 lumens per watt and that halogen incandescent can provide 20 lumens per watt or a bit more).
It is also worth considering that Cree's best reported laboratory performance for a cool white LED is currently at 208 lumens per watt. If this could be translated into commercial LEDs, a bulb/fixture efficiency of over 150 lumens per watt would be feasible. Such performance (and even somewhat better) is almost certain to become available, but there is no guarantee as to when. It is good to have a handle on not only what is possible now, but also on what may be coming in the future.
Most of the LED bulbs found in the store at this writing can look pretty anemic. Clearly, it is not fair to compare them to the brand new XP-G, but LEDs like the Cree XR-E have been readily available for some time and, using our 75% factor, these could provide bulb efficiencies of 55 to 70 lumen per watt as we span from warm to cool white. In comparison, many retail products list efficiencies of between 20 and 40 lumens per watt and some bargain products don't even provide lumen ratings. There are some specialty products that cite higher performance capabilitiesin the neighborhood of 50 to 70 lumens per watt or a little better. Such numbers (when accurate) suggest the use of good LEDs and pretty careful design. But they still pale in comparison to the 77 to 100 lumens per watt that are attainable from the new XP-G LEDs. Considering the cost of LED-based products, this is a very important thing to consider.
With these numbers in hand, we can also make a sensible comparison to other options. First, consider compact fluorescent (or CFL) bulbs. To draw a baseline, we can refer to the government's voluntary "Energy Star" program which certifies products that meet minimum energy efficiency requirements. The minimum required CFL values are between 55 and 65 lumens per watt, depending on the wattage of the bulb. The potential efficiency of CFL will likely improve somewhat more with time, but note that these numbers are for bare CFL bulbs. The standards for fixtures and floodlights are lower to allow for the optical losses which result from things like lenses and reflectors.
When it comes to fluorescent fixtures based on traditional tubes, the Feds have mandated the use of newer, more efficient tubes and ballasts (electronic power supplies). The new "T8" tubes are skinnier than the old familiar ones and they offer efficiencies of 80 to 100 lumens per watt. Another alternative in some situations is "metal halide" (basically the same thing as "HID"). Efficiency here can be around 100 lumens per watt. Sodium vapor can provide 120 lumens per watt where its familiar yellow color would be acceptable. Another advantage of these choices is that they can provide a lot of light for a reasonable cost. It would require a number of high tech LEDs to provide the several thousand lumens that can be had from a two-tube T8 fluorescent fixture and that can get expensive.
Focusing lenses can squeeze the light from an LED into a tighter pattern and this can be particularly useful for work lights (note that the light itself is visible as the dot of light at far right). We'll examine this and other details related to building LED-based lights in the next article.
In a nutshell, we find that a number of inexpensive, readily available alternatives can equal or beat the best currently available LED-based lights in terms of raw efficiency. Of course, this simple comparison ignores important considerations like the efficient dim-ability of LEDs or their potentially long service life. If you are starting with LED and CFL alternatives of comparable efficiency, but you would be happy with half-brightness except for intermittent needs like reading, card playing, eating, meal preparation, etc., then the LED option could prove vastly superior in the end. Operation at half-brightness could cut the power load by better than half and the cooler running temperature of the gently powered LEDs could mean a service life of well over 50,000 hours with little or no loss of output. On top of all this, the "directional" nature of an LED's emission could make it more efficient in the delivery of light and allow you to get better final lighting with fewer starting lumens. In order for LEDs to actually deliver these advantages, proper design is essential. For instance, many commercially available LED bulbs are not dimmable. In addition, a dimmable LED light will only be efficiently dimmable if the electronics are suitable.
This evolving technical situation means that a big project requires some careful thought. For instance, a person planning an off-grid home or big cabin could consider CFL bulbs (AC or DC) as a long-term-temporary solution until LED technology develops a little further. It should be noted that the standard screw-in bulb is not necessarily the best platform for LEDs because of their directional light emission and heat management issues. As a result, fixtures designed specifically for LEDs will probably provide the best performance in the long run. Thus, it might be best to mate the stop-gap CFLs with cheap plastic or ceramic lampholders instead of buying more expensive light fixtures with the idea of screwing in replacement LED bulbs in the future.
A problem with many of the high-efficiency options is that they are most readily available for use with 120-volt AC power. But considering them is still important, because it gives us an idea of what to look for when considering DC products suitable for direct battery use. RV and marine suppliers are often a useful source of such lights and there are also ones marketed specifically for off-grid uses. In addition, there is also the option of buying AC-based lights and using an inverter to power them. With a big project, this may be the final approach because of the need to power other appliances. When using this strategy (especially with smaller, portable inverters), take care to check compatibility. The AC current synthesized by inverters is not exactly the same as the stuff that comes out of a standard wall outlet. But if you need a lot of light, a proper inverter and off-the-shelf AC lights from the building supply store could prove to be both the cheapest and most efficient lighting strategy in some cases. Regardless of your choice with respect to a power source, it is important to assess the actual efficiency of the specific lights you are considering. The simple fact that a light is based on CFL or LED technology is not a guarantee of any particular lumen per watt efficiency.
LEDs will likely prove to be the hands-down choice for both off-grid and conventional lighting at some point in the future. But even then, there will still be more and less efficient choices, as there are now. For the time being, we also have to add in a careful comparison of other available technologies. As I said in Part 1, there are no easy answers here, but being armed with the right information is the essential starting point.
In Part 3, we will consider the alternative of building your own LED lights from components. This strategy can be particularly useful because it can allow you to put the best available LEDs into packages that will fit your specific needs. In addition, we will also consider the efficient use of light.
LED Technology Update
Brightness isn't everything, at least in some cases: the new "HP20" headlamp from Fenix (left) uses the XP-G LED, but its maximum output of 230 lumens is about the same as the "HP10" model (right) which is based on the older XR-E LED. By powering the new LED more gently, runtime from four rechargeable AA batteries is stretched from 2.5 hours to 3.5 and the heat-related limitations of the older model (see the "Headlamp" section) are avoided. These particluar examples also illustrate the importance of fitting other design details to your needs: the HP10's battery pack is attached to the back of the headband while the HP20's is separate and must be belt or pocket carried. An attached pack provides for more compact storage, quicker deployment, and the avoidance of cord-related snags and tangles. But a separate pack means less weight on your head, a potentially nice feature during extended use. It also allows the batteries to be kept inside a warm coat during cold weather operation.
Common LED suppliers
Seoul SemiConductor Corporation: www.seoulsemicon.com
www.light-reviews.com is a review site that contains reviews of a large number of LED-based flashlights.
www.candlepowerforums.com is a web forum that contains a lot of information on LED technology and products.
I am familiar with these product sources and confident in their reliability:
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