Princeton Tec EOS LED Headlamp REVIEW

Product performance review of the Princeton Tec EOS 1-watt LED headlamp.


by Rick Dreher | 2005-03-01 03:00:00-07


Princeton Tec EOS Headlamp - 1

The Princeton Tec EOS is a high-performance headlamp that's suitable for technical nighttime activities. It is by far the brightest LED headlamp in its size and weight class, and the lightest 1-watt LED we've tested; 3.7 ounces (105 g) with three AAA alkaline batteries, 3.3 ounces with lithium batteries.

At its brightest setting, the EOS will satisfy cross-country backpackers and climbers who want their adventures to continue after sunset. With alkaline cells, the three AAA batteries maintain brilliant light for over three hours (nearly five with lithium). A more useful setting is medium where the EOS puts out nearly 15 hours of surprisingly bright light (suitable for difficult trails and off trail travel and comparable to heavier AA powered 1 Watt LED headlamps). The EOS can eke out at least three continuous days (72 hours) from a single alkaline battery set when used on low, all the while providing ample light for in-camp chores and simple nighttime navigation. The EOS maintains a reasonably steady light output as battery voltage drops, delaying the progressive dimming that plagues flashlights of all kinds with current regulation circuitry.

Our test sample survived multiple 3-foot drops to the ground and lived up to the maker's claimed 1-meter waterproofness rating. It is simple to operate with a single switch and an easy-access battery compartment. The adjustable elastic headband and ratcheted lamp-angle pivot keep the EOS's beam aimed at the desired spot during most activities.

In Brief

  • Very bright single 1-watt Luxeon white LED gives 15 continuous hours of very bright light on medium mode with lithium batteries and 3 to 4 days of quite useful light when set on low
  • Electronic current regulation for sustained light output as batteries wear
  • Single, glove-operable recessed switch for on/off and all modes
  • Three brightness levels plus one flash mode
  • Ratcheted lamp tilt angle and adjustable headband length
  • Rated waterproof to 1 meter


• Headlamp type

Integrated lamphead and battery pack, adjustable angle

• Light source

Single 1-watt Luxeon LED, fixed beam angle

• Run time (measured)

5.5 - 72 hours total; 2+ hours of undiminished high output

• Modes

Three brightness levels, one flash mode

• Batteries

3 AAA alkaline (provided) or lithium cells

• Weight

3.7 oz (105 g) with alkaline cells, 3.3 oz (94 g) with lithium cells, 2.5 oz (71 g) without batteries as measured; 3.7 oz (105 g) with batteries manufacturer specification

• Head strap

Single, adjustable elastic

• Battery access

O-ring sealed, hinged access door, locks with thumbscrew


$38.99 Manufacturer's suggested retail price


The rugged plastic-bodied EOS uses a single collimated Luxeon white LED in four usage modes - from low to very bright, and flash. Rather than a hybrid configuration combining a high-output LED for technical lighting with one or more low-output LEDs for low-light uses, the EOS simplifies matters by using the single LED and adjusting the current to it. This approach helps keep down weight, bulk, complexity, and cost.

The EOS lamphead is combined with the battery compartment as a single unit - there's no external battery compartment or power cable. The 1-inch-wide elastic head strap threads through a baseplate that's connected with a hinge to the bottom of the lamphead, providing a vertical angle adjustment. This hinge is ratcheted to hold the angle, and the adjustable-length head strap is long enough to fit a helmet. There is no top strap. The EOS is comfortable on a bare head, with no noticeable pressure points and few hair-snagging features. The lamphead baseplate strap holes are slotted, enabling easy strap removal and replacement so it's easy to use the lamp without the strap, wash the strap, or replace it.

The EOS's clear acrylic lens is recessed in the bezel to help protect it from scratching. The top-mounted multi-function switch is also recessed, which helps in locating it by touch and prevents accidental switch operation when the EOS is stowed. The switch operates the four EOS modes in series: high, medium, low, and flash, then off. A roughly two-second pause in any mode leaves it in that setting, with the next press switching it off. The 80 flashes per minute flash mode operates at the bright setting. Because the EOS has no mode memory, each use requires scrolling through the settings to select the desired level.

The battery compartment door is hinged and permanently attached to the case. The compartment can be accessed by unscrewing a slotted, knurled aluminum thumbscrew and then swinging the door open (a screwdriver, coin, or other tool will fit in the slot if needed). The thumbscrew is captive to prevent its loss and it screws into a threaded brass insert in the lamphead body, eliminating the possibility of stripping out soft plastic threads. An O-ring seals the battery door and it requires care to ensure that the slender O-ring is clean and fully seated in its groove before closing the door. The O-ring is easily damaged if not aligned properly. Batteries are held tightly in place, helpful in preventing their tumbling to the ground when the compartment is open. A shield behind the batteries protects the electronics. This second barrier should help keep stray moisture and, more importantly, battery leakage away from the light's circuitry.

Function and Fit

The adjustable 1-inch strap is comfortable. In most circumstances, it stays in place without requiring that it be cinched uncomfortably tight. In general, heavier headlamps balance better when the battery compartment is separate and either attached to the back of the strap or kept in a pocket or on a belt, but smaller integrated headlamps such as the EOS usually don't feel especially front-heavy. Normal campsite activity and walking or hiking don't cause enough bounce to move the EOS strap or slip the angle setting, but nighttime trail running does cause some movement. Lacking an angle lock or a top strap, the EOS can't shrug off as much impact as headlamps that have these features. However, if you're not competing in the Western States 100 you may never find this to be a problem. Using a spare piece of elastic or webbing, EOS owners can easily thread a top strap into the light's strap mount and attach it to the main strap in back, further securing the headlight in place.

The switch can be operated wearing fleece mittens. With a certain concentration and dry conditions, batteries can be changed while wearing liner gloves. Operating the screw is easier than digging out the used AAAs.

Constant Light Output

All flashlights, unregulated and regulated, incandescent or LED, gradually dim from the time they're fed fresh batteries. At its most dramatic, this dimming is noticeable to the eye and quite rapid - some flashlights dim to a useless orange glimmer in as little as an hour. To counter this tendency, the EOS current regulation circuitry works to maintain the light output as the batteries wear down. In our tests the EOS halted much of this progressive dimming in low and medium modes, and slowed it when set to high. Lithium battery output was significantly steadier than alkaline, consistent with their comparative discharge characteristics. As with all LED lights, the EOS's color temperature doesn't change as output drops, as occurs with incandescent flashlights.

Beam Pattern

The EOS has one of the most focused beams we've tested. It concentrates almost all light in a very small center spot. This accounts for some of its exceptional on-center brightness even at low battery levels. Driving a 1-watt LED is no easy task with AAA batteries.

Table 1 - EOS Performance at 2 Feet Distance, Alkaline Batteries, 70 &degF
Intensity Setting Beam Center (lux) 1 foot Off-Center (lux)
High 1,250 4
Medium 490 3
Low 125 2

Fresh Alkaline Batteries, Room Temperature (70 °F)

Note: Values varied somewhat over the duration of our tests.

The EOS beam is a narrow, bright, circular center spot surrounded by a much dimmer circular halo that provides a little flood lighting. The warm white light exhibits none of the color fringing, unevenness and odd artifacts that emanate from most white LED flashlights; the absence of purple is most noticeable. The beam pattern rather resembles a polar view of Saturn: the center spot representing the planet and the broader halo, the rings. There's a thin, dimmer band separating the two (possibly just an optical illusion).

This beam configuration has certain advantages over either a pure spot or a pure floodlight. The bright center projects for a long distance and, for example, lights up a trail quite effectively yards ahead while the dimmer halo illuminates off-axis details that might be invisible using a pure spotlight. In camp, the halo eases chores because you don't have to carefully aim a small spotlight at the area of attention. For routine tasks, especially close in, the center spot can be distracting. As an example, the light isn't ideal for nighttime reading because the bright center spot on white paper can dazzle the eye, and it illuminates only a portion of a page. Hanging the light and aiming it at the book helps by spreading the beam further, as does diffusing it with a piece of tape, paper or cloth.

Most any camp chore can be performed on low, which also adequately illuminates clear trails. Rough or indistinct trails are maneuverable with the medium setting, and high makes even difficult nighttime cross-country travel feasible. Demanding users may find they're able to navigate on medium for almost any terrain, reserving high for those times when they need the extra illumination for a difficult spot, much as one uses a car's high beams. This will mean hours more battery life.

Battery Life

In order to gain a sense of EOS performance in different uses and conditions, Backpacking Light tested several battery-output-temperature permutations. They are summarized in the performance graphs and table. We found that the EOS will run continuously for a minimum of about 2.5 hours at high output, and for several days to over a week on low. Alkaline cells work well, and lithium cells perform even better at less weight but greater cost. The EOS outperformed the Princeton Tec specifications at all settings, in certain instances impressively so.

Princeton Tec EOS Headlamp - 1
The EOS's ability to provide fifteen hours of bright, stable light on medium was perhaps the most remarkable result of all our tests.

Princeton Tec EOS Headlamp - 2
The EOS had an output of 40 lux after three days (72 hours) on low with alkaline batteries at 70 °F. We found we could still perform chores and follow a clear path at this output, but after another ten hours output dropped to roughly 10 lux and remained there through day 9 (216 hours). 10 lux is very minimal light, but still useful with night-conditioned eyes for certain simple chores.

Table 2 - Time Performance Summary (hours:minutes)
    Princeton Tec specification Alkaline batteries 70 °F, measured Alkaline batteries 38 °F, measured Lithium batteries 38 °F, measured
High Constant 2:00 2:30 3:30 4:30
  Total 6:30 6:00+ 6:00+ 5:30
Medium Constant 9:30 Not Tested Not Tested 15:00
  Total 12:30     15:30
Low Constant 44:00 48:00 Not Tested Not Tested
  Total 60:00 72:00    


All measurements were taken from 2 feet away, recording the brightest portion of the beam (highest possible continuous reading).

"Constant" refers to a constant output level (lux) before output drops off.

Like batteries were the same brand, same batch.

Our test cutoff times were often arbitrary, due to the need to begin the next test phase. In all cases where we let it run, the EOS continued to shine for days after dropping below 50 lux.

Translating the Results

Princeton Tec's hours-of-performance claims appear to be legitimate. What's more, their estimate of ultimate battery life far understates how long the EOS will actually continue to emit useful light ("useful," of course, is in the eye of the beholder). Alkaline cells work well in the EOS, lithium cells even better. EOS current regulation is very effective on low and medium settings, and fairly effective on high; it works better with the lithium batteries than with alkaline batteries. Demanding users (e.g., wintertime climbers and cavers) who require high output can expect nearly 5 hours of continuous use with lithium cells before the EOS output drops to the medium output value. If they can navigate using medium instead of high, they can expect as much as 15 hours continuous output, meaning it's unlikely they'd need to change batteries while on the move. Medium provides a good balance between illumination and run time for difficult navigation chores. The EOS's ability to provide 15 hours of bright, stable light on medium was perhaps the most remarkable result of all our tests.

The EOS had an output of 40 lux after three days (72 hours) on low with alkaline batteries at 70 °F. We found we could still perform chores and follow a clear path at this output, but after another ten hours (82 hours) output dropped to roughly 10 lux and remained there through day 9 (216 hours). 10 lux is very minimal light, but still useful with night-conditioned eyes for certain simple chores.

It was apparent in all cold-condition tests that after the test began, the EOS was warmer than 38 degrees - the LED and perhaps the circuitry were evidently warming it. That low temperatures had little negative effect on alkaline battery life, and seemingly aided performance at certain points, was a surprise. It might be that higher temperatures (ambient plus light-generated heat) actually harm battery performance, or, the light's internally generated heat - normally thought of as wasted energy - might actually play a role in extending battery life when the battery compartment is integrated into the lamphead. Note that the EOS lacks a lamphead heatsink, frequently used on LED headlamps that have a separate battery pack. The EOS appeared to "break in" and became slightly more efficient with use. We performed the high power, alkaline batteries, and room temperature test initially and at the test's end. The second test had a higher initial brightness, held the output above 1,000 lux for longer, but dropped past the low output level sooner than in the first test.

Less surprising but no less gratifying was lithium performance, which maintained rock-steady light output for hour after hour. Please note that more-extreme conditions (subfreezing, windy) will measurably shorten battery life, especially alkaline.

Because nearly all flashlight use is intermittent, our continuous-use tests give worst-case results. You can expect cumulatively greater battery life from the EOS than our data indicate when using it on a typical backpacking trip. Those of us who've become accustomed to using a single set of batteries in an Aurora or Tikka for a summer's worth of backpacking, might still be able to do so with the much brighter EOS, provided we're frugal about using the high mode. Given the excellent output on medium this is not much of a hardship.

Torture Testing

The EOS lived up to Princeton Tec's claim of being waterproof to 1 meter, as an hour in a fishpond demonstrated. Grazing carp were evidently unimpressed by its flavor. A few drops - inadvertent and intentional - onto wood and concrete from about 3 feet demonstrated its ruggedness. The lens cover of our test lamp has gathered a few hair-fine scratches which don't seem to affect the beam.

Compared To...

We're rather stunned at how quickly the Princeton Tec Matrix 2 (reviewed here) has been bettered by the new EOS in every way. Compared to the Matrix 2 (now discontinued), the EOS is lighter, smaller, and makes more efficient use of batteries. In our tests, the EOS at medium output is about as bright as the Matrix 2 but gives more consistent light output. The EOS also coaxes hours more life from near-dead batteries. The EOS at high power is brighter than the Matrix but does not run as long. Compared to the EOS on high power, the initial Matrix 2 center-beam brightness is two-thirds that of the EOS (792 lux warm, 604 lux refrigerated) but the Matrix 2 sustained a greater percentage of this initial brightness hours longer (with alkaline cells). As we've noted before, we recommend that you use the high mode of the EOS sparingly. The Matrix 2 has a single output mode compared to the EOS's four modes, which allow for intelligent lighting levels and battery conservation.

Compared to the Princeton Tec Aurora (reviewed here), the EOS is much brighter (based on our tests, the Aurora is roughly one-fifth as bright) but weighs 1.0 ounce more. The EOS's switch is easier to operate, with or without gloves, the battery compartment is both better sealed and easier to access, and the electronics are better protected. It's easier to see correct battery alignment (polarity) on the EOS. The EOS is larger and heavier and exhausts batteries more quickly (depending on the mode you use). The Aurora lacks the EOS's current regulation and its protective convex plastic lens is exposed and easily scratched. The Aurora's beam has a less dramatic transition from center spot to the edge, making it a better floodlight and conversely, a less effective spotlight. The Aurora hums and strobes on medium and low settings, and causes radio interference.

Technical Bits


Princeton Tec has selected a rather special LED for the EOS; it appears to be a Star/O model made by Luxeon, a pioneer in high-performance LEDs. (Princeton Tec notes their having worked with Luxeon in customizing this LED for their purposes.) The LED "emitter" sits in collimating optics (a sort of reflector) and generates an approximately 10-degree wide beam with the distinctive bright center and surrounding halo. This configuration is reminiscent of a standard flashlight, but in this case, the emitter and collimator are combined into a single sealed unit.

Current Regulation

The EOS current-regulating circuitry works to help maintain a constant power supply as batteries wear and the voltage drops. Typical alkaline cells begin life at 1.5 volts and steadily drop until their eventual death somewhere around 0.8 volts; lithium cells also drop to about 0.8 volts over time, but they hold their initial voltage much longer (a difference more pronounced as temperatures drop). In the EOS, this means that an initial battery-supplied 4.5 volts drops to below 3 volts as the batteries wear out. The regulation circuitry works to keep voltage closer to 4.5 for a much longer time than with unregulated batteries.

We found the current regulation to be reasonably effective at maintaining light output as time passed, especially at the medium and low settings. It was perhaps most impressive with lithium cells at medium, where output was solid for nearly 15 hours! With alkaline batteries at the high setting, the EOS settled at one level for only about an hour and a half. Alkaline cell voltage drops precipitously in high-drain conditions, and the EOS circuitry can't completely overcome this shortcoming.

Although there's no way to be certain, the lack of a performance drop in our cold-temperature tests may also be partially attributable to current regulation. Because the EOS doesn't wink off completely when the batteries near exhaustion, it doesn't descend to uselessness with very worn batteries. The light emitted can be compared to that of a button-cell flashlight with less-than-new batteries: just bright enough for close-in tasks, nothing more. Still it's a lot better than a dead light.

The medium and low settings don't appear to "strobe," hum, or cause radio interference, as do many other LED flashlights sporting dimmer settings. This is cause for celebration for those bothered by these little annoyances, and could be a great boon to cavers and search and rescue folks who rely on radio communications.


The bright beam center can dazzle the eyes, even on low. Predawn climbers, or cavers who know they'll need extended periods of high-output performance may need to change batteries on the go, as the EOS will only produce roughly 3 hours with alkaline cells or 5 with lithium (before output drops below medium). The ratcheted angle setting could prove too loose for trail runners because the constant bouncing can cause it to drop, requiring adjustment. Similarly, the single band can slip on the head.

Recommendations for Improvement

  • Provide a way to lock the lamp angle.
  • Offer a removable top strap and a snap-in red lens for preserving night vision.
  • To aid night vision and reduce button pushing, provide a last-use mode memory so the light can be directly switched on to low.
  • "Trap" the O-ring in its groove so it's held captive and unlikely to be damaged when changing batteries.


The Princeton Tec EOS represents the pinnacle thus far in the rapid evolution of LED headlamps. It's small, light, bright, and waterproof. It's comfortable and easy to operate. It's bright enough for any foot-powered nighttime activity. Even on medium, it's plenty bright for following sketchy trails. Despite the dazzling output, the EOS doesn't consume batteries by the fistful, and its current regulation circuitry helps maintain useful light output for an extended period as batteries fade. The low-power setting is adequate for most camping activities and can support weeks on the trail from a single battery set. Moderately cold temperatures don't hamper EOS performance, and lithium cells work especially well, helping assure rock-steady light output.

Can there be any doubt that with the advent of lights like the EOS, there's no longer a market for halogen backpacking flashlights? Call it high-tech wizardry; we call it the best high performance-to-weight headlamp yet!


"Princeton Tec EOS LED Headlamp REVIEW," by Rick Dreher. (ISSN 1537-0364)., 2005-03-01 03:00:00-07.