Petzl has revised its method for determining headlamp lighting ranges and burn times. With the objective data provided by this new method, Petzl headlamp users will now be able to better choose the model that best suits their needs.
Petzl believes that the minimum amount of light needed for most activities is similar to the amount of light emitted from a full moon on a clear night. Our lighting ranges and burn times are calculated using this minimum lighting value as a benchmark.
Why a reference system?
Petzl developed this lighting reference system provide users with objective comparative criteria and dependable, precise data and it will help them choose the right headlamp. This reference measures the performance of headlamps in a scientific and reproducible manner.
It is inspired by empirical data, drawn from in-the-field experience.
^How does it work?
From our point of view, the minimum amount of light usable for most activities is equivalent to the light emitted (the illuminance) from the full moon on a clear night, or about 0.25 lux.
All of our measurements use 0.25 lux (as measured directly in front of the headlamp) as a benchmark.
The reference is based on two elements that measure the essential performance of a headlamp:
- distance (light range)
- light duration (burn time)
Determining the distance
We define the light
range as the distance at which the light beam maintains 0.25 lux.
As the headlamp is used, the batteries' power diminishes and the light range decreases. We therefore state the light range of our headlamps at the following stages of battery life:
- with new batteries (the headlamp's maximum capacity)
- after 30 minutes use (standard usage)
- after 10 hours use (equivalent to continuous use during one night)
These data are presented like this:
t0 = 17 m
t30mn = 14 m
t10h = 8 m
Some of our headlamps have a current regulator. This electronically maintains the light output at a constant level during most of the batteries' life. When the batteries are nearly drained, the light automatically switches to a reserve power mode.
- Non-regulated LED lighting curve
- Regulated LED lighting curve
For these particular headlamps, we state the light range and burn time for which they are electronically regulated. For example, 10 m during 30 hours:
10 m → 
30 h
Determining light duration
We define light duration as the total time (in hours and minutes) that the headlamp produces a light that provides at least 0.25 lux at 2 meters.
When the light produced is less than 0.25 lux at a distance of 2 meters, we consider the headlamp no longer usable (whether for walking, reading or any other activity).
^What does this mean for Petzl headlamps?
Current light range and burn time information may change. That does not mean that our headlamps have changed, but simply that the headlamp information is more precise due to this new measurement method.
Headlamp light range and burn time information calculated using this new reference system will be marked with the symbol above.
In the future...
Petzl will strive to provide more information regarding the shape, evenness and quality of the light emitted from our headlamps.
^Measurement method
Recall:
- Distance = distance in meters at which the illuminance is 0.25 lux.
- Light duration = time (in hours and minutes) during which the light at 2 meters is greater than or equal to 0.25 lux.
Distance
The formula that we use to calculate light range: E = I / d²
- E =
- the illuminance, in lux.
- I =
- luminous intensity, in Candela.
- d =
- distance, in meters.
With a light meter, we measure the illuminance (E) of the headlamp at a distance of 2 meters (d = 2).
We use this value to calculate the luminous intensity (I) of the headlamp (I = E x 2²). With
the luminous intensity (I), we can calculate the distance at which the headlamp would produce light
equal to 0.25 lux (d = 
I
/ 0,25).
Exemple
E = I / d²
We start by measuring the illuminance of the MYOLITE 3 at 2 meters (d = 2 m). We find an illuminance to be 360 lux (E = 360 lx).
To calculate the luminous intensity (I) of the MYOLITE 3 : I = E x d² = 360 x 2² = 1440 cd.
Therefore, the total light distance of the MYOLITE 3, d = I / E = 1440
/ 0,25 = 75,8 m.
Light duration
We measure the headlamp's burn time by placing it 2 meters from the light meter with fresh batteries. The elapsed time that the headlight emits a beam stronger that 0.25 lux is known as the total burn time.
^Glossary
- Luminous flux
- Energy per unit time that is radiated from a source over visible wavelengths.
- Lumen (lm)
- Standard unit of luminous flux.
- Luminous intensity
- In general, a light source emits its luminous flux with a different intensity depending on the direction it is shined. The luminous intensity is a measure of the energy emitted by a light source in a particular direction.
- Candela (cd)
- Standard unit of luminous intensity.
- Illuminance
- The total amount of visible light illuminating a point on a surface from all directions above the surface.
- Lux (lx)
- Standard unit of illuminance (lumens per square meter).