Lighting Reference System

What is a lighting reference system?

Black Diamond, key headlamp suppliers and retailers came together recently to build a single system for measuring light output and burn times. That means that as you try to compare the brightness and battery life settings of headlamps of different brands you should find the measurements calculated using the same system, making it easier for you to cross compare models and make the right buying decision.

The limits: It’s impossible to find a measurement system that captures all the important features of light output and light duration. The current system favors lamps that have a strong center point of light and does not take into account the overall shape of the light output or the strength of the light output outside of the center point. Therefore a lamp that projects a very strong pinpoint of light with a very weak surrounding beam might receive a longer, farther distance rating than a lamp that offers a stronger wide beam with very strong pinpoint center.

What does it measure?

The first step in measuring light output is determining the minimal amount of light needed to perform an activity. We call this minimal amount of light usable light. Usable light is defined as the light provided from a full moon on a clear night. As a base reference, this has been calculated to be 0.25 Lux (lumens per square meter).

In all measurements of battery life and distance, 0.25 lux from a distance of 2 meters serves as the baseline.

The Lighting Reference System rates headlamp performance based on two criteria: distance of the beam and battery life.

Distance = Distance light can reach and still provide 0.25 lux of light at the center point.

Battery Life = Battery life is measured as the amount of time the lamp will illuminate a single axis point with 0.25 lux measured from 2 meters distance.

Distance – How to calculate

Distance, measured in meters, is defined as the distance a light can reach maintaining the output of 0.25 lux. As battery power is used, the distance the light project at a minimum of 0.25 lux will decline (current can be regulated to provide a unique light projection pattern). Distance is measured at the following time intervals:

t = 0 h  Initial brightness (to be recorded within the first 5 minutes of turning the lamp on)
t = 0:30 h  The average amount of use a light 30 minutes after start-up
t = 10 h   The amount of light after a full night of use (10 hours)
t = x h   Additional points of time to measure Distance

We provide Distance specifications in the following format:

Testing Procedure for Distance

Five lamps are each tested with 2 sets of batteries of the same brand provided at retail. The average of the 10 data points collected is what is published on our packaging and website.

To calculate the beam distance, measure peak intensity at 2 meters at the optical axis or brightest point in the beam pattern using a constant power source where the input voltage is equal to the battery input.

For example: 4AA batteries = 6 volts
                    2 AA batteries = 3 volts

Use the inverse proportion formula to calculate the distance the light source will provide 0.25 lux.

To calculate the beam distance at each of the time periods T

EXAMPLE:

1. Measure peak luminance of the light source at 2 meters (d =2 m). 
(For this example we assume the luminance is 200 lux)

2. Calculate the intensity
(The intensity is: 200 lux x 2² meters = 800 candela).

3. Calculate the square root to obtain the distance
(Working backwards: .25 lux is the square root of (800/0.25lux)=56.6 meters

Battery Life

Battery Life, measured in hours, is defined as the amount of time the lamp will illuminate a single axis point with 0.25 lux measured from 2 meters distance. Battery life is listed in hours and rounded to the nearest 30 minutes.

Testing Procedure for Battery Life

Measure light output at time t = 0 hours using a power source of constant voltage equal to the output of the battery system intended for the lamp. Place lamp in a fixture that is set at 2 meters distance from the light sensor and lower the voltage of the power source until the light output from 2 meters is 0.25 lux. A multimeter is used to measure the voltage going into the lamp while the lamp is producing 0.25 lux at 2 meters. 

To test battery life, insert fresh batteries of the same brand and type as the batteries included with the product. Turn the lamp “on” and start the time monitoring the time expired until the voltage of the batteries is the same as the voltage read when the light meter measures 0.25 lux. If batteries are not included with the product use Energizer® or Duracell® alkaline batteries or whatever battery is recommended on the  packaging or instructions. If the lamp has an auto-shutoff feature manually restart the lamp within a minute after it automatically shuts off.

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