Just finished reading through the whole post
It’s a pretty big coincidence that we both build a light with the black flat at almost the same time
I am almost finished my build, just waiting on some liquid metal thermal paste.
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“Minimum distance for accurate measurement of luminous intensity:
Many of you know that one cannot measure the true luminous intensity (throw) of a thrower in 1m distance it the value is supposed to be accurate. The reason for this is that in this distance in some lights the reflector is not completely lit up by the LED as seen from the sensor of the lux meter. One has to go further away and adjust the value for the longer distance. TLF member sma once studied this in more detail here (link is external). We both have the theory that it depends on the difference in size between the reflector and the LED. I have tried to calculate this for my light based on his results with an Olight SR-95 UT.”
I have done some testing, it’s pretty interesting actually.
If you take a piece of paper, poke 3 small holes in it, and put it in front of the reflector/lens of a flashlight you will get 3 separate squares (the die image) projected onto a wall.
In “infinite focus”, which is what you want for ideal maximum throw, these three squares will be centered exactly at the 3 points.
To get a proper lux reading when focused like this, the lux meter needs to be placed at the center, and the flashlight needs to be far enough away that all squares overlap in the middle, including the ones from the outer edges of the lens/reflector.
With this exaggerated huge LED example, all squares would overlap at 1.1m (so you would measure slightly farther than that)
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However, with a focusable lens or reflector, you can actually change the focus and make all squares overlap at the luxmeter.
When they are all overlapping is when you get the “sharp die projection” image.
This allows you to take the measurement at a closer distance and get the same cd value when you calculate it back to 1m.
You need to keep in mind though that focused at the luxmeter will not give maximum throw. It should be collimated using that template I posted above for best throw.
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For your flashlight, I calculated a minimum distance of 28.5m when it is collimated correctly.
If you want to know how I calculated this stuff just let me know, I can make a separate topic explaining everything.
To measure the maxabeam, I’m not sure how far it would need to be, because unlike an LED the small burning point is not all the same intensity like the surface of an LED is.