Light Output

Light Output is the total luminous flux. It is the total quantity of emitted overall light energy as measured by integrating the entire angular output of the portable light source. Light output in this standard is expressed in units of lumens.



Beam Distance

Beam distance is defined as the distance from the device at which the light beam is 0.25 lux. (0.25 lux is approximately the equivalent of the light emitted from the full moon “on a clear night in an open field”).


burn time


Burntime is the duration of time from the initial light output value—defined as 30 seconds after the point the device is first turned on—using fresh batteries, until the light output reaches .25 lux for headlamps, or 10% of initial output for flashlights and lanterns. This testing procedure was agreed upon by several headlamp manufacturers in 2002.


regulated LED

Regulated LED

Some Princeton Tec lights feature regulated circuitry that maintains initial brightness as long as the batteries have sufficient voltage. Traditional lights are very bright initially, but begin to dim immediately and continue to dim until the batteries are drained. Constant Brightness is a term used to describe products that have regulated LEDs.



Regulated vs. Non-regulated