The Princeton Tec EOS Bike is the only bike light we've tested that can also be used as a headlamp. The light slides on and off a screw-on handlebar mount or an elasticized headband. In theory this design could save you money because you could use one light for biking, hiking, and camping. But in reality we found that the light performed relatively poorly as a bike light and also below average as a headlamp. Most importantly, the light's very poor battery life (3.6 hours) makes it very expensive to operate over the long-term. Many other bike lights have USB rechargeable batteries that are more convenient for bike commuting and also much cheaper to own over time.
Princeton Tec EOS Bike Review
Cons: Relatively narrow beam pattern, moderately bright, terrible battery life, relatively heavy for a headlamp, no battery life indicator.
Manufacturer: Princeton Tec
Our Analysis and Test Results
As you can see in the photo below, this light has a moderately wide and moderately even beam pattern that does an OK job at lighting roads and trails. Other lights, such as the Metro 360 (at right below), have a much wider and more even beam pattern that make them considerably better for biking and hiking.
This light is only moderately bright and gets a 4 out of 10. We measured its maximum distance at 60 meters compared to the Metro 360 which reaches 135 meters. Though the light is effective for short and mid range viewing, it would perform considerably better if it were brighter and could shine farther.
It's small and reasonably lightweight. The bike mount is simple and effective, but doesn't allow you to swivel the light on the handlebar. The mount needs to be screwed onto a handlebar and is therefore not as easy to move to another bike when compared to lights with tool-less attachments.
This light has very poor battery life, a mere 3.6 hours according to the ANSI FL-1 standard. Brightness declines dramatically around the three-hour mark, and the light holds a very low (read: not usable for biking) light level for an additional nine hours.
For most people, this is a significant drawback and also a nuisance if you're on a multi-day overnight trip because you likely need to carry extra batteries, which are heavy.
The high operation costs and moderate performance makes this light a poor value.
— Chris McNamara and Max Neale