Buying a flashlight/spotlight?
I need one to read street signs from my car, so I'd need a 12v (or less) light and I want 300 lux at 10 meters distance.
Here's a list of HD lights
212 . . . .186
61 . . . .82
208 . . . .126
125 . . . .53
111 . . . .47
134 . . . .388
450 . . . .400
I assume the distance given [the beam throw] is when the beam illumination falls to 1 lux [E], the light of a full moon.
Unfortunately, they do not give beam angle, which ties this all together.
But, it may not be necessary.
For 1 lux, the beam candlepower [I] is the distance [R] squared, so the third column is calculated based on the distance.
Lumens distance calc'd beam candlepower
212 . . . . .186 ........34596
61 . . . . .82 . . . .6724
208 . . . . .126 ........15876
125 . . . . .53 . . . .2809
111 . . . . .47 . . . .2209
134 . . . . .388 ........150544
450 . . . . .400 ........160000
Now, I want 300 lux for reading the sign and I = E * [R^2] and so at 10 meters I need 30,000 beam candlepower.
The first and last two lights should work. This last one is a Maglite that can be focussed from flood to spot.
I have tried many of the expensive $125 and up lights from streamlight to Cree. I am now using an Led Maglight and it seams to do the same thing, but only costs $30.
If that helps.
I would buy the less expensive Maglight with 2 D cells, first, and see how it does. It makes a great backup light when the other rechargables die.
HD hardly had any lights that were not LED.
I'm already having some doubts about my numbers & assumptions so I'll have to run some experiments.
I'm more certain about going between lumens, beam angle and candlepower. Back to the drawing board on this beam throw idea. . .:(
Thanks to Maglite posting Lumens, beam candlepower [cd, probably standing for candela] and throw, if you know beam candlepower you can figure out throw.
The formula is
Throw = (0.007212541 x cd) + 120.5950053
for the range 5000 to 38,000 cd and throws of 140 to 390 meters, with a max error of 11% and average error = 0.7%.
Therefore, for one of these 1,000,000 candlepower lights the throw should be 7300 meters, without knowing the beam angle.
I can't check this because I burned out the bulb in my spotlight while trying to run it off of 12vac. It was operator error. :(
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