Princeton Tec EOS Headlamp
Field Report
Report Date: March 1, 2005
My initial report may be viewed here
Reviewer Information
- Name: Edward Ripley-Duggan
- Age: 51
- Gender: Male
- Height: 6' 1" (1.85 m)
- Weight: 215 pounds (98 kg)
- erd@wilsey.net
- Catskills, New York State
Reviewer Background
I enjoy walking in all its manifold forms, from a simple stroll in the woods to multi-day backpack excursions. Though by no means an extreme ultra-light enthusiast, from spring to fall my preference is to carry a pack weight of 12 lb, 5.5 kg (i.e. before food and water), more or less. In recent years, I've rapidly moved to a philosophy of "lighter is better," within the constraints of budget and common sense.
Product information in brief
- Manufacturer: Princeton Tec
- URL: http://www.ptsportlights.com/
- Product: EOS Headlamp
- Year of manufacture: 2004
- MSRP: US $38.99 (from press release)
- Batteries: 3 AAA
- Manufacturer's stated weight: 3.7 oz (105 g) with standard AAA batteries
- Measured weight (digital P.O. scale): 3.7 oz (105 g) with standard AAA batteries
- L.E.D: 1 watt Luxeon with Princeton Tec designed lens/collimator
- Light settings: four modes, three standard at varying levels of intensity, one flashing
- Method of control: "active current control circuit"—from the package enclosure
- Battery life (based on use of alkaline cells, taken from corporate press release):
- High output mode–2 hours of constant brightness / 6.5 hours of run time
- Medium output mode–9.5 hours of constant brightness / 12.5 of run time
- Low output mode–28 hours of constant brightness / 36+ of run time
- Waterproofing: "1 m waterproof" according to package (no standard cited)
Field and Test Information
For this field report, the Princeton Tec EOS headlamp was used extensively for "day" hikes (ending well after dark) and backpacking trips in the Catskill and Adirondack Mountains of New York State, at elevations to 4500 ft (1370 m). Much of the hiking involved off-trail excursions and included a number of the more difficult Catskill peaks. For reasons of winter safety, minimum pack load was 15 lbs (5.4 kg) or so for day hikes and up to 28 lbs (11.3 kg) for backpacks.
The lowest temperatures experienced during the testing period were at elevation, at approximately -10 F (-23 C). The winter (and the testing period) began with very mild conditions, but intensified in mid-January with a period of intense cold and deep, dry snow. This was followed in early February by a period of remarkable warmth, with temperatures at elevation of close to 45 F (7 C). One could fairly characterize the weather for the Field Test period as bizarre.
Product Use and Performance
Some general observations
A headlamp is a critical part of the basic equipment of the serious hiker and backpacker. I have led too many hikes during which someone tried to illuminate their way along an icy path holding a torch, usually with the predictable result of a slip or fall, with the dropped torch skittering downhill (this actually happened on a hike I led during the Field Test period). For safety, a good powerful headlamp that leaves the hands free for balance, self-arrest or other tasks is far and away the best tool.
L.E.D. (Light-Emitting Diode) headlamps now have a huge advantage over those with bulbs, in that they make a far more efficient use of battery power. This in turn conserves weight, as fewer batteries are needed. Within the past year I have seen the technology come a long way. Last year's L.E.D. units produced adequate light, but that tended to be somewhat bluish in tint. This year, L.E.D. "bulbs," such as the Luxeon used in the EOS, are twice as bright and produce light with much less tint. "White" L.E.D. devices actually use a blue L.E.D., surrounded by plastic. They contains a layer that absorbs and re-emits the light in such a fashion that a certain portion is converted to other colors of the spectrum. While the result is not exactly chromatically equivalent to white, they are now, at this point of development, probably closer than many torch bulbs. While tint is not a critical issue, it does have bearing on such tasks as map-reading.
How bright is "bright?"
The critical part of testing a headlamp is how it performs in the field. However, as headlamp technology becomes increasingly sophisticated, some other measures of performance are useful in addition (not least because the eye is rather poor at determining relative brightness, etc.). I had previously developed a methodology for testing light output at various temperatures during another headlamp test. I have applied the same methods here
Light output from the EOS was measured in lux, the International Standard (SI) unit of measure for luminous flux density at a surface, using an inexpensive digital light meter. A distance of two feet between the front of the lamp housing and the light meter's sensor was chosen for the test. This enabled the brightest region of the beam to coincide with the light sensor's dome. The measuring unit has a stated accuracy of +/-5%. A refrigerator and freezer provided the constant cold temperatures required.
As a key aspect of the EOS is the circuitry designed to control the voltage supply to the diode, and hence maintain its brightness as a constant level, my tests involved charting how well this technology worked at the available light settings (excluding the flash setting). The 150 lux level shown on the charts below is equivalent to an intensity that I had (on a previous test) determined to be barely adequate for trail walking, allowing blazes to be seen but at no great distance. I have taken it as the minimum useful level of illumination. The following chart shows the output of the EOS over time at the three brightness settings, as an indication of the time one can expect the headlamp to provide useful light. The temperatures noted are the ambient air temperature; the lamp itself may be slightly warmed due to heating effects by the diode (some heat is generated, as well as light).
On the maximum brightness setting, when at room temperature, the EOS's circuitry keeps the light at constant brightness for approximately two hours (allowing for error, shown by the +/-5% vertical error bars). There is usable light for approximately eight hours. The two-hour period is in line with the manufacturer's claimed time. At the middle brightness setting (adequate, as I have noted in the field, for most things except serious bushwhacking), the light level remains constant for ten hours, before dropping off, though at least two hours of usable light remain (time constraints prevented me from depleting the output to the 150 lux level). This is also in line with the manufacturer's specs. At the lowest setting, enough light for careful trail walking over moderate terrain (and basic camp tasks) was generated at an almost invariable output for at least twelve hours, and I have little doubt that the manufacturer's claim of 28 hours of constant illumination at this level is accurate. Things get more interesting when one goes to lower temperatures.
The pattern shown on this chart is typical of low-temperature lamp performance. At the maximum brightness setting at 40 F, 12 C, only one hour of constant brightness was produced. Usable light was produced for slightly in excess of six hours. At 10 F, 4 C the voltage correction circuitry could not keep pace with the rapid battery drain at all (and the initial brightness was much reduced). The light output of the lamp was depleted after a mere four hours. This is not a weakness of the headlamp, it should be noted, but of alkaline batteries. The chemical reaction that is responsible for creating electrical current is highly dependent upon the temperature of the battery. Clearly, if one is going to use the lamp in cold weather with alkaline cells, one must use the lower brightness settings and conserve use as much as possible.
The solution? Lithium AAA batteries are rather expensive but I have been using them with this lamp in these winter months, and with them the performance of the lamp at low temperature is roughly comparable to that with alkaline cells at room temperature (see plot above). For winter hiking and backpacking the extra cost is money well spent. In addition, they are slightly lighter! However, it should be noted that, once they start to become depleted, performance drops far faster than with an alkaline cell; they discharge in a very different manner. Still, I was provided with full-intensity light for well over three hours (I tested quickly at the 3.5 hour mark, and was still obtaining full output).
Out of the "lab" and on the trail!
Eos was the Greek goddess of dawn, and while the Princeton Tec EOS headlamp can't rival the rising sun, it is certainly bright! On one hike during the Field Test period, I needed to illuminate a rugged snowy trail for two members of my group. This the EOS was able to do very capably on maximum output. The only disadvantage (true with any headlamp, especially so with L.E.D.s) is that anyone turning to look in my direction risked being painfully dazzled
The distance at which illumination is effective is something that's difficult to evaluate absolutely (and which is, in any case, dependent on atmospheric conditions) so I am not going to attempt to assess the utility of the lamp in terms of how distant an object could be illuminated, but rather its overall utility at the various brightness settings. The full-power setting proved bright enough for just about any activity, on or off trail. It was adequate for bushwhacking over rough terrain, if correctly angled, showing up any sudden ledges well ahead of time, and with enough power that one could scan them to find the best point of ascent or descent. On this setting, if I blundered off a winding trail, as I did at one point, sweeping the surrounding woods was sufficient to spot a missed blaze. It's a comfortable feeling to have this sort of lighting power at a finger's touch. It proved adequate for some moderately serious backcountry cross-country skiing, as well as hiking.
The middle brightness setting was adequate for some use off-trail on less demanding sections, and was sufficient for any trail I encountered. Fairly distant blazes (in this area, plastic disks) showed up well. The minimum setting is more than adequate for general camp use, and good for reading. Additionally, it's possible to walk on trail quite comfortably even at this level, with a little care. I tested the flashing mode. It flashes at maximum brightness; however, the beam, because it is focused, is rather directional. Placed on top of a tent, it made the campsite obvious without wasting battery power, but in my opinion this mode should be used only as an adjunct method of attracting attention in an emergency.
The manner in which the beam is focused by the collimator is worthy of mention. A high percentage of the light output is concentrated at the center of the beam; which is really where it is wanted. Sufficient light is dispersed to the sides to allow for some degree of illumination of the periphery, and this is useful. Also, as mentioned previously, the quality of the light emitted by the diode is very good. Though it tends slightly to the blue end of the spectrum (as an incandescent bulb tends to the red) the light is really a better approximation of white than I have generally encountered in headlamps of any kind. I have noted very little distortion of color values, which I find impressive.
Other practical notes
The headband is very easily adjusted, and provides a tight, stable fit, even over a winter hat (the hood of my jacket, or my Gore Windstopper bonnet). On bushwhacks (where it is very easy to have a headlamp dislodged by a branch) the lamp stayed stably on my head. While I tend to keep the band fairly tight, I find the lamp perfectly comfortable to wear for periods of several hours at a time. I tried setting the band to the head of one of my daughters; it is easily adjusts to any head size. It even fits a plastic helmet reasonably firmly.
Changing the batteries is straightforward; using the thumbscrew at the rear of the lamp housing accesses the battery compartment. This may be firmly tightened (if preferred) by using the buckle on the headband, which fits into the slot on the screw. The lamp swivels through almost ninety degrees, from the straight-ahead position to a point where it is pointed down at the ground. There is a ratchet mechanism (not externally visible or accessible) that allows the angle to be changed in increments of about twelve degrees. It's very easy to select a position that illuminates the terrain ahead to the necessary extent, as I found when skiing with the lamp on. Because of the ratchet the lamp, once correctly angled, tends to stay locked in position. One minor cavil I have with the unit (as with many headlamp designs) is that it does not rotate up beyond the horizontal.
As this Field Test was conducted over winter (admittedly a rather eccentric one, with periods of unseasonable warmth in January and February) I have not yet been able to test the lamp in rain. The waterproofing of the battery compartment (and the circuitry) is effected by means of a rubber gasket that sits in a groove molded in the lid. One point of minor concern is that (in my lamp at least) this gasket is a poor fit, and is loosely seated. It bulges out of its track slightly. While I do not think this will substantially diminish water resistance, I feel this worthy of note and I will be watching this carefully. I'm concerned that the gasket may potentially become completely unseated and even dropped in the process of changing batteries. It would be virtually impossible to remount with gloved hands (and easily lost against a background of forest duff or similar).
While on the topic of gloves, I have tried operating the switch using a light fleece glove with a silk liner, with a heavy glove with an insulated liner, and in mountaineering mitts. Wearing the first two, switching the lamp on proved fairly easy, although slightly harder with the insulated gloves, naturally. Predictably, it proved a more awkward task wearing mitts, but it was still possible to turn the lamp on and off and alter the brightness mode. Changing batteries wearing the mitts was not really feasible, but was simple enough wearing gloves.
Despite heavy use over the Field Report period, the lamp still looks pretty much as new. It has been dropped a couple of times (though not terribly hard) but doesn't seem unduly sensitive to shock.
Summary
Likes
- Bright, controllable illumination at a low weight.
- Comfortable and easy to adjust.
- Excellent quality of light, with minimal color distortion.
Dislikes
- Gasket that can easily become displaced or detached.
- Lamp does not rotate up beyond horizontal.
Future Testing Strategy
In my further testing over the next four months, I will examine the following aspects.
1. How waterproof is the lamp in heavy rain?
2. Does the ratchet mechanism hold up to wear (there is no method of externally tightening this if the lamp becomes loose).
3. Does the lamp continue to be durable overall?
Most of the points in my initial testing strategy have been addressed in this report, however I'm sure there will be plenty of observations to be made for the Long Term report as I refine my knowledge of this lamp.
I thank BackpackGearTest and Princeton Tec for permitting me to participate in this extremely interesting and enjoyable test.
