How DO they measure flashlights? — Inverse square law confirmed

[rlhess]

Hi,

I have been bothered by the claims of 1MCP in spotlights and other high claims in flashlights. I keep wondering how they measure these.

I set up a test tonight with my UKE SL6. We do know from the IES handbook that beams don't necessarily form in the first foot or two so I've taken to measuring bigger lights at 10 feet.

Anyway, I measured my SL6 at 10 feet and at 50 feet. Interesting, I got 110 fc at 10 feet and 4.37 fc at 50 feet. If you multiply 110*10*10 you get 11,000 cd. If you multiply 50*50*4.37 you get 10,925 cd.

Of course the 10*10 and 50*50 represents distance squared (10^2 or 50^2).

So with the Brinkmann measuring 65,000cd and the Vector measuring 100,000cd how can these be 1,000,000 cp (cd)?

I find the same thing with Mag lights (but not quite as bad--not 10:1).

I'm still trying to figure out the mechanism these people use.

I can think of one--but I want to give them the benefit of the doubt.

Cheers,

Richard

 

[DonL]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by rlhess:
... I'm still trying to figure out the mechanism these people use.

I can think of one--but I want to give them the benefit of the doubt.

Cheers,

Richard<HR></BLOCKQUOTE>

The "Roulette Wheel of Illumination?" A quick game of "Candlepower Darts"? "Marketing-biased SWAG"?

I wish there was some sort of consistency as well...

 

[rlhess]

Don--you thought of three along the lines that I was thinking. It really was a serious technical question.

I know how we all measure lights and my results don't come very close to the results in the ads, but do come close to what the others with light meters are getting.

Thanks for the smile!

Cheers,

Richard

 

[Jonathan]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by rlhess:
Hi,

Anyway, I measured my SL6 at 10 feet and at 50 feet. Interesting, I got 110 fc at 10 feet and 4.37 fc at 50 feet. If you multiply 110*10*10 you get 11,000 cd. If you multiply 50*50*4.37 you get 10,925 cd.
<HR></BLOCKQUOTE>

Yes, but you are multiplying by the wrong factor. These lights are rated in _inch_ candles, not the less precise _foot_ candles. So you should be multiplying 110*120*120, which gets you well past that pesky million mark.

*grin*

-Jon

 

[rlhess]

And how do inch-candles get translated to candlepower (candela) or do they assume that candlepower is the inch-candle equivalent of candela?

 

[DonL]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by rlhess:
Don--you thought of three along the lines that I was thinking. It really was a serious technical question.

Richard<HR></BLOCKQUOTE>

Well, it's become my nature to be a cynic at times. I think that the same fuzzy marketing is behind one of those most famous phrases, "your mileage may vary."

I'll have to look around in a testing and specification database I have access to and check if there's any specific test standard concerning lumination.

For example, Title 49, Part 571, Section 302 of the Federal Code of Regulations deals specifically with Federal Motor Vehicle Material Flammability testing standards and procedures.

Similarly, ISO (International Standards Organization) 11357-1 pertains to the determination of the melt point of a material by differential scanning calorimetry testing.

They're all ways of ensuring some sort of "standard temperature and density" conditions so that all data is compared as not only apples to apples, but Granny Smiths to Granny Smiths and not Jonathans.

If there were to be such a move within the industry, there'd be no more of this hodge-podge of guessing games.

I'll report back when I have an opportunity to study this in more detail.

 

[DonL]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Jonathan:
Yes, but you are multiplying by the wrong factor. These lights are rated in _inch_ candles, not the less precise _foot_ candles. So you should be multiplying 110*120*120, which gets you well past that pesky million mark.

*grin*

-Jon<HR></BLOCKQUOTE>

But what if they measure it in millimeters?