Hey!
i know the usage of the max. setting is controversal - which are your experiences with that?
also - feel free to post your suggestions!
my goal was to have reproduceable results to compare FLa to FLb and FLc
Thank you for the video. The information below is from a friend of mine who is an engineer and very, very knowledgeable.A simple minded person like me can understand his explanation. Hopefully it can help ALL of us.
The important things to remember on Lux, to get a representative cd, is to measure it far enough away so that the beam has had time/room to form.
IE: The cd is the lux at one meter, but, measuring the lux AT one meter is almost always wrong to get the cd, because for the throwy lights, the beam may not REPRESENT the true cd until it is even 20 meters away.
We want REPRESENTATIVE cd values, because we use the cd to calculate how bright the spot will be on distant targets…to know if we could SEE SOMETHING at those ranges.
If the cd can be plugged into the calculation, and predict the lux on a distant target, its a good number.
Generally, the best way to FIND the representative cd (What the ANSI methods are supposed to be telling you), is to measure the lux at the brightest part of the beam (central typically) at various distances to find the distance at which the cd stops rising/levels off.
The lux will tend to drop as you move further away from the light (Due to inverse square law), but, the cd can rise even as the lux drops….because the cd takes the distance into account.
For most of the lights, if measured at 20 meters for example, the beam will have formed by then. Just multiply the measured lux at 20 meters by 400 to get the lux at 1 meter (the cd).
So, if you get 250 lux at 20 meters, that means the light has a cd of 100,000, and so forth.
For your lux meter, generally, it will be most accurate at the central part of its range/range with best resolution…so, typically, a more distant reading will reduce the measured lux to the meter’s best resolution.
BELOW was s suggestion from him to another flashaholic who was ONLY measuring from 7.5 meters.
Just to RE-Clarify:
Just because they are measured at 7.5 meters DOESN’T mean they are comparable numbers, EXCEPT at 7.5 m.
The reason is, again, the distance required for the beam to fully form.
This is WHY the 1 m numbers are always low for example on a good thrower, and we back calculate TO 1 m equivalent….and measure at a longer distance.
So if Beam A is fully formed at 6 m, and Beam B is fully formed at 15 m, and BOTH are measured at 7.5 M and back calculated to 1 m (cd), then, Beam A’s cd number might be accurate, and Beam B’s cd number might be lower than it really is.
If both are measured at 7.5 m, and Beam A is fully formed at 10 M, and Beam B is fully formed at 15 M, BOTH cd will be lower than they really are, but NOT necessary by the same amount…or with one 33% less, etc.
The DEGREE of beam formation is NOT necessarily the same, as every beam has its own collimation formation pattern. So, you really CAN’T compare the cd of all of them at 7.5 M UNLESS they ALL form NO FARTHER AWAY THAN THAT.
Well, you can COMPARE them all you want, its the conclusions you’d draw that would be suspect if expecting too fine a differentiation between lights.
The problem is, you’d need to know the cd to know if the light was more, or less, likely to NEED more distance, and, ironically, that’s what you’re trying to find in the first place.
If there’s ONLY 7.5 m max ROOM to measure, ok, its a limiting factor…but try not to over weigh the results when comparing hard throwers to each other unless you DO KNOW the minimum beam formation distance.
You only need the center of the hot spot/max lux spot to measure, the rest doesn’t affect the cd.
Nice video Martin!
Why do you use cardboard around the meter? To eliminate readings from daylight? It might affect the reading, it’s better to close the curtains or measure when its dark enough.
To get a representative number it is best to use the same setup with multiple distances, so you can see whether the readings are consistent. i use a tripod to have a stable setup and measure the light at 5m and 10m on my white garage door.
That was what I was looking for 
Do you color the pipe inside in black or white, or it doesn’t matter?
i will try that and let you all know
I thought the same, until I tired to verify that claim. While it absolutely makes sense it is just not the case. Even lots of 1mcd throwers do not need more than some meters to have the beam fully formed.
Try it
whats your cooked down suggestion?