Guide: Measure beam distance for your flashlights in a few easy steps
Table of contents: Jump to the following sections
- A reliable Lux meter
- A tool to measure the distance (A tape measure or a laser distance measure)
- A computer or calculator (we can use a useful online tool to help with this)
- The calculation
- Extra tool to consider: a headlamp
Hints and tips before you do your first measurements.
The goal of this page is to help you understand how to measure your flashlights for maximum beam distance and beam intensity.
Fortunately, there are standards that flashlight manufacturers can use for their specifications with regard to Lumens and Candela. These are known as the ANSI-NEMA FL-1 standards. With your measurements, you try to use those standards to know what your flashlights are capable of.
In order to know your candelas, you need 2 numbers: Lux and Distance. The higher the intensity of your flashlight, the farther away the lux meter should be away from the flashlight. Generally speaking, the best distance for long-range flashlights, including LEP Flashlights, is 20 meters or more. Although we want to know the candela at 1 meter, you should never measure at 1 meter. Measurements at that close distance are extremely unreliable due to the beam divergence.
The second thing I would recommend is selecting a spot you can use repeatedly. You can even mark down a certain distance with a pen/marker for your next round of measurements. The key is to be consistent with all your measurements.
The third thing I would recommend is using a laser distance measure and not a tape measure. I've been there, done that. Too much hassle, especially in the dark. Buy yourself a laser distance measure (even a cheap one) and thank me afterward. The second reason is the ability to measure in Ft as well as in Meters. Most normal tape measures in the US measure in inches and feet, not in meters.
The last tip may sound retarded, but always make sure the battery/batteries are fully charged. Don't assume it's fully charged, check it. It happened to me more than once.
3 steps process
Step #1 - Measure the Lux
1: Choose an object like a wall to focus the beam on.
- Tip: Make sure it's flat since that helps to move the sensor through the beam without changing the distance from the flashlight too much.
2: Use the laser distance measure to get a distance of 20 meters or more.
- Tip1: (It doesn't need to be precisely 20, 25 or 50 meters since you need to calculate it back to 1meter anyway.
- Tip: When your sensor of the lux meter is 2 cm thick, you can add that to the distance if you'd like to be more precise.
3: Make sure the flashlight stays at that exact distance.
- Tip: Use a tripod or put the flashlight on something stable like a chair. Flashlights tend to roll around. I sometimes put it on the ground on a piece of old carpet or on a piece of wood.
4: Walk to the wall and find the highest lux reading by moving the sensor through the beam slowly.
- Tip 1: when you turn on your flashlight, start counting to 30, when you slowly walk to the wall (or object). Continue counting while finding the brightest spot in the beam. When you reach 30 seconds, write down the highest lux number you found. You can also use a timer.
- Tip 2: Don't use a piece of paper, but use your hand to write the numbers down. Sound silly? Trust me, if you drop that paper you wish you listened to me.
- Tip 3: Use a headlamp so you have less chance to trip over something and always have enough light to write down the lux numbers. Trust me, LEP flashlights have a very tight beam, and while the beam is extremely bright and intense, you will have trouble seeing anything in the dark after looking at the beam during the measurements. There is almost no spill that helps to navigate in the darkness, plus the beam is likely to mess your vision in the darkness.
- Tip 4: I recommend also measuring the other modes you want to check. Most LEP flashlights only have 1 or 2 modes. So not really a big deal.
The picture below is just an example.
Step #2 - Calculate the candelas
You have your lux numbers, now what?
A candela rating is nothing more than the number of Lux at 1 meter.
Example: you measured the lux of your LEP flashlight at 20 meters to be 1500 Lux
The first thing you need to calculate is the lux numbers at 1 meter.
There is a simple formula for this = LUX x DISTANCE x DISTANCE
In our case, this would be 1500 lUX x 20 METERS x 20 METERS = 600,000 lux.
(The Lux measurement at 1 meter equals the candela rating)
So 600,000 lux = 600,000 cd.
And 600,000 cd = 600 kcd
BONUS TIP: FREE ONLINE CALCULATOR
Instead of doing the math yourself, you can use this online calculator as well.
POSSIBLE PROBLEMS DURING MEASUREMENTS:
It's possible that your calculation will be off. You know why?
Most Lux meters use a multiplier. In that can you first need to multiply your measured Lux number by the multiplier. Take a look at the following images. All 3 Lux Meters use multipliers. The last picture shows a Lux number of 833 but with a multiplier of x10. In that case, the lux number is actually 8330, and you have to do the calculation with 8330 instead of 833. Please note, this was just a quick example and not from a real LEP measurement at 20 meters.
Step #3 - Calculate distance in meters / yards / miles
While you have your measurements in Candela, you can use the following formula to calculate your beam distance in meters.
(You already learned that lux at 1 meter equals Candela)
We need to divide the Candelas by 0.25 and use the Square Root of that number.
600,000 cd / 0.25 = 2,400,000 and the square root of 2,400,000 = 1549.19 meters.
TIP : instead of dividing the Lux number by 0.25, an easier approach is to multiply it by 4. Same conclusion: (600,000 x 4 = 2,400,000)
Overview of a list with candela, beam distance in meters, yards and miles
|100,000 cd (100kcd)||632||692||0.393|
|1,000,000 cd (1 Mcd )||2000||2187||1.243|