Princeton Tec EOS FR-TED
- The following FR is posted on the TEST page for your reading pleasure
(?) <g>. I aware of the date discrepancy and will correct it on the
final edit. Yahooisms &c.
Report Date: March 1, 2005
My initial report may be viewed here
* Name: Edward Ripley-Duggan
* Age: 51
* Gender: Male
* Height: 6' 1" (1.85 m)
* Weight: 215 pounds (98 kg)
* Catskills, New York State
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
* 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
* Battery life (based on use of alkaline cells, taken from
corporate press release):
* High output mode2 hours of constant brightness / 6.5 hours
of run time
* Medium output mode9.5 hours of constant brightness / 12.5
of run time
* Low output mode28 hours of constant brightness / 36+ of run
* Waterproofing: "1 m waterproof" according to package (no
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 turns 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 a plastic that contains materials that absorb and
re-emit 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 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 angles, 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 missing 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 focussed, 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
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.
* Bright, controllable illumination at a low weight.
* Comfortable and easy to adjust.
* Excellent quality of light, with minimal color distortion.
* 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.