Measuring Candlepower on an LED???

[lawyerjess]

Can anyone explain (preferably in layman's terms) how you measure candlpower, i.e., what tools one might use to measure it and if that process is the same on an LED light? Can someone "eyeball" the candlepower of a given light source???

 

[Optical Inferno]

You need an Integrating Sphere and detector setup. This works for fixtures too, but most lights don't use "candlepower" as a unit of reference. They typically use Lux, Footcandles, etc. For that you typically want a Lux Meter. You can't eyeball candlepower, and if you try with the right light source you can cause permanent damage to said eyeball.

Check out Gigahertz Optik for an example of the meters.

 

[SemiMan]

You need an Integrating Sphere and detector setup. This works for fixtures too, but most lights don't use "candlepower" as a unit of reference. They typically use Lux, Footcandles, etc. For that you typically want a Lux Meter. You can't eyeball candlepower, and if you try with the right light source you can cause permanent damage to said eyeball.

Check out Gigahertz Optik for an example of the meters.

You do not use an integrating sphere to measure candlepower, only lumens.

You use a light meter to measure candlepower. If you know the lux and distance and assuming the sensor is evenly illuminated, then you can work out the candlepower.

Semiman

 

[Echo63]

Semiman is correct.

Candlepower is just Lux measured at 1m
for example, a light that shows 100,000 lux at 1m has 100,000 CP

Also bear in mind that CP is really only a measurement of the brightest spot in the beam, and tells you nothing about the actual beam, only how it will throw.

Most lights are too bright to be measured at 1m, and many don't actually focus a proper beam until the beam gets out a few metres, so it is possible (and frequently done) to measure at a longer distance, and calculate the lux back to 1m (I can't remember the exact formula though)

I measured my Maxabeam a few years ago, and it measured out at 7.2million CP
that tells you nothing about the beam shape though, other than the hotspot is very bright.
Adding that it's only about 1200-1500 lumens, allows the presumption that it's a very throwy beam (which it is, often described as a white laser)

Heres a pic of the beam, shining a kilometre , you can see the minimal spill on the ground too, on a normal light that would be a very bright white

 

[lawyerjess]

So what do you make of this phraseology???

"a beam of light of an intensity greater than 300 candlepower shall be so directed so that no part of the high intensity portion of the beam will strike the roadway at a distance of more than 75 feet."

If I understand correctly (which is quite possibly not the case) then candlepower has nothing to do with the beam and cannot be measured that way, which would make the language quoted above irrelevant.

 

[Echo63]

So what do you make of this phraseology???

"a beam of light of an intensity greater than 300 candlepower shall be so directed so that no part of the high intensity portion of the beam will strike the roadway at a distance of more than 75 feet."

If I understand correctly (which is quite possibly not the case) then candlepower has nothing to do with the beam and cannot be measured that way, which would make the language quoted above irrelevant.

Ah, given the username and this question, I'm going to assume you are in court dealing with vehicle headlamps.

What I understand that to mean is - if the light produces more than 300lux@1m then the beam must be aimed down, so the furthest edge of the bright spot is closer than 75ft to the vehicle, much like the low beam on a vehicle headlight.

automotive headlamps produce beam patterns much different to flashlights and spotlights, and this is probably a question better suited to the Automotive lighting subforum, and the experts there

 

[RoGuE_StreaK]

This thread may be related?

 

[SemiMan]

So what do you make of this phraseology???

"a beam of light of an intensity greater than 300 candlepower shall be so directed so that no part of the high intensity portion of the beam will strike the roadway at a distance of more than 75 feet."

If I understand correctly (which is quite possibly not the case) then candlepower has nothing to do with the beam and cannot be measured that way, which would make the language quoted above irrelevant.

It means exactly what it says. No part of a headlight beam that is over 300 candlepower (which is an intensity measurement) can be aimed further than 75 feet in front of the vehicle.

If you got caught with a HID kits and are trying to fight a ticket ..... well then no sympathy will be found here.

Otherwise, auto forum is a great place.

 

[Bullzeyebill]

This thread has been moved to the Automotive, Motorcycles Included forum.

Bill

 

[-Virgil-]

You will probably get a fair number of answers to your question. Most of them will be wrong (so far the answers you've gotten in this thread as to what the language means have all been incorrect). The language in question is common to many US states' vehicle lighting equipment and usage statutes. There are very specific, particular meanings it does (and doesn't) have, and its actual, legal meaning can only be interpreted in conjunction with other portions of code (which specific other portions depend on the actual code and actual lighting device in question). If you go to court with advice you pick up on an internet forum, even from an expert, you will likely get demolished. Best to check with a consulting expert in the field for reliable interpretation of the statute as it actually applies. Try Daniel Stern and/or Rich Van Iderstine.

 

[Optical Inferno]

You do not use an integrating sphere to measure candlepower, only lumens.

You use a light meter to measure candlepower. If you know the lux and distance and assuming the sensor is evenly illuminated, then you can work out the candlepower.

Semiman

OOps...yeah your right. Don't know where I was that day. My bad.