# Maximum possible candle watt power



## mattf765 (Oct 25, 2011)

I'm sure this question has been posed before but... I need a spotlight to shine from my truck occasionally when coming home from work. I live in rural Indiana and drive on many country roads. I need a light that can shine a long way across plowed fields. Any suggestions on candle watt power? Or is CWP just a marketing gimmick? Should I be looking at lumens? I was unaware of how in depth the world of flashlights/spotlights was. Any suggestions are greatly appreciated.


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## FRITZHID (Oct 25, 2011)

well, how far out in the field do you need to see? once you reach a certain point, the light may reach but your vision can't make out whats lit up anyway.


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## Norm (Oct 25, 2011)

mattf765 said:


> I need a light that can shine a long way across plowed fields.



Which leads us to this thread Illegal to shine flashlight in fields? 

Norm


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## BVH (Oct 25, 2011)

mattf765 said:


> I'm sure this question has been posed before but... I need a spotlight to shine from my truck occasionally when coming home from work. I live in rural Indiana and drive on many country roads. I need a light that can shine a long way across plowed fields. Any suggestions on candle watt power? Or is CWP just a marketing gimmick? Should I be looking at lumens? I was unaware of how in depth the world of flashlights/spotlights was. Any suggestions are greatly appreciated.



Matt, give us an approx distance you need to cover. Is it 500 Yds, 750 Yds? And what objects do you want to be able to see at that distance? And yes, claimed candlepower is just that, a wildly inflated number. The typical 10,000,000 MCP light is actually about 300,000 to 500,000 if you're lucky. Lumens produced and how it is focused (floor or throw) is a better way to figure out what you might need.


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## tpopz2908 (Oct 25, 2011)

BVH said:


> The typical 10,000,000 MCP light is actually about 300,000 to 500,000 if you're lucky.



Yep, however there are a few corded spots that are rated pretty honestly:

Lightforce, the SL 240 is rated at 1mil I think. It can throw light farther than you can see and is overkill in most situations for us. We prefer the SL 170.

Collins Dynamics or Havis. I used the CD-Magnums and CD-12's for years but they are pretty heavy and expensive. 

Both of these will out-throw just about any "10 million candlepower" incan spotlight.

Throwing a SL240 out over someone elses field will certainly attract attention.


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## xul (Oct 25, 2011)

mattf765 said:


> I need a light that can shine a long way across plowed fields. Any suggestions on candle watt power?


lamp with 
1000000 candles _ luminous intensity 
illuminates a spot with 
1 lux ,E (full moon overhead in the tropics)
How far away is it? 
R=sqrt(I/E) 
1000 =calc'd distance in meters, R_


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## mattf765 (Oct 25, 2011)

Most of the land I would be shining a light in is my own land. And no I'm not "spotlighting." I do hunt but I'm just curious as to the wildlife in my fields. I'm talking at the farthest 750 yards. Would like something durable enough to leave in the truck year round in all weather conditions.


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## JacobJones (Oct 26, 2011)

Hmmm, 750 is quite a long way. Do you have a budget???


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## xul (Oct 26, 2011)

mattf765 said:


> I'm talking at the farthest 750 yards.


~0.5 million cp.
You know the spot diameter you need? A 40' diameter [1 degree beam angle] is probably ambitious.


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## mattf765 (Oct 26, 2011)

I suppose 750 yards is a bit ambitious, especially at night. More like 3-400 yards at most. Budget is not really an issue so much as durability and dependability. Don't know much about beam angles but I assume spot diameter is diameter of the light at a given distance? Max distance? I suppose I'd like to have a wider diameter than narrower.


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## xul (Oct 26, 2011)

lamp illuminates a spot with 
1 lux, E
at 
300 meters, R
or 
328 yards
with candlepower, I, is E(R^2) 
takes 
90000 cp

a spot 
100	feet in diameter, SPOTDIAM	
at distance 
1000	feet, RANGE	
gives a beam angle, BA, of 
2xARCTAN(SPOTDIAM/2xRANGE) 
5.724810452	degrees	

And thank you to Mr. Combs for suggesting a second look at what seemed to be simple geometry.


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## ZeissOEM2 (Oct 30, 2011)

xul said:


> lamp with
> 1000000 candles _ luminous intensity
> illuminates a spot with
> 1 lux ,E (full moon overhead in the tropics)
> ...


_

[email protected] 1 m - and how much lux at 458 meters ?? 
Some people maybe wants to know how to take it the other way- the calculation . _


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## xul (Oct 30, 2011)

ZeissOEM2 said:


> [email protected] 1 m - and how much lux at 458 meters ??
> Some people maybe wants to know how to take it the other way- the calculation .


R = sqrt(I/E)
R^2 = I/E
I = E(R^2)
E = I/(R^2) = 1000000/(458^2)= 4.8 lux.

Since the 1 million is probably only known to one significant figure this final result should be reported as 5 lux. The 458 is known to three significant figures but the final answer is limited by the number that is the least precisely known.


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