9200 mcd led equals what in a bulb or lamp?

[N4aeq]

I have some Nichia 9200 mcd white leds.What does
mcd equal to in a flashlight bulb? or how do i
convert it to candlepower?
Radio shack has a small list of their PR base
bulbs but there output is listed in (mscp)? Whats
this? Is there a chart anywhere on the web with led & bulb output listed the same way? Or anyway.Im just trying to make a comparison of multipule leds to various flashlight bulbs.

 

[INRETECH]

mcd is "Milli-Candela", you divide by 1000 to get the candlepower

For example, 9200 mcd is 9.2 Candela
One of NiChia's brightest, I might add

Most Lightbulbs are rated in Lumens, which is measured differently - although you can convert lumens to Cd by:

Lumens X 4pi -> Candela

Mike
www.inretech.com

 

[Jonathan]

Originally posted by INRETECH:
Most Lightbulbs are rated in Lumens, which is measured differently - although you can convert lumens to Cd by:

Lumens X 4pi -> Candela

Mike

<font size="2" face="Verdana, Arial">Mike, you have posted this before, and it is _not_ correct.

Lumen are a measure of the _total_ light output in all directions from a lamp.

Candela are a measure of intensity in a particular direction.

They are related, because you can measure the intensity (in candela) in _all directions_, add these values up (appropriately scaled for angle)(properly, integrate the intensity values), and calculate flux in lumen.

You can only equate lumen and candela if you know the light intensity distribution. The equation that you supplied should be:

Lumens / 4pi = Mean Spherical Candela

And this equation _only_ gives you the average intensity distribution. If the light source is putting the same intensity out in all directions, then Mean Spherical Candela will be numerically equal to candlepower.

The perfectly spherical distribution of light is very much _not_ the case with a 9200 mCd LED. These LEDs put most of their light out into a narrow beam, with the intensity in other directions being quite a bit less than 9200 mCd.

The total lumen output of a White Nichia 9200mCd LED is about 1 lumen, and the mean spherical candlepower is about 0.1 (both numbers _very approximate)

-Jon

edit: sorry for sounding huffy or singling you out; this is just one of those basic fact things that can press a button now and then. I do appreciate the work that you guys are doing putting out nifty LED lights.

 

[INRETECH]

I am aware of those facts, Candelas and Lumens are two different ways to measure brightness; but just as Lb and Kg are different ways to measure weight, we need a means to convert between them if only a crude formula

I know this from experience as well, I recieved some 13,000 MCD LEDs and found out they had a 1-degree beam width

Mike
www.inretech.com

 

[star882]

"I know this from experience as well, I recieved some 13,000 MCD LEDs and found out they had a 1-degree beam width"
What color are those?
I am sure they put a spot on the wall similar to a laser pointer(but not as good).

 

[brightnorm]

Isn't it also possible to multiply watts times the approximate watt/lumens efficiency ratio for a particular light source, whether incandescent or LED? Even though a very rough approximation, wouldn't it give at least a ballpark figure?

Brightnorm

 

[Doug S]

Originally posted by INRETECH:
I am aware of those facts, Candelas and Lumens are two different ways to measure brightness; but just as Lb and Kg are different ways to measure weight, we need a means to convert between them if only a crude formula
Mike
www.inretech.com

<font size="2" face="Verdana, Arial">Mike, the "facts" that you think you are aware of are not facts. The point that Jonathan was making is that only Candelas are a measure of "brightness" [intensity]. Lumens is a measure of something entirely different [flux].

 

[Jonathan]

Originally posted by INRETECH:
I am aware of those facts, Candelas and Lumens are two different ways to measure brightness; but just as Lb and Kg are different ways to measure weight, we need a means to convert between them if only a crude formula

<font size="2" face="Verdana, Arial">Good point, a crude approximate formula is actually quite useful.

Please note: what I am about to present is still only an approximation, one which I suggest is better than the mean spherical candela conversion, but still only approximate.

To properly convert candela into lumen, you need to know the intensity values in all directions from the light source, and to integrate over the entire sphere. The integral of intensity (measured in candela) over the solid angle of interest (measured in steradians) is the light flux (measured in lumen).

If we make the approximation that the intensity of a light source is perfectly even in a circular cone, and perfectly zero outside of that cone, then the integration is particularly simple: we simply determine the solid angle of the cone, and multiply that by the candela value. For example, if the light source is a 1 candela source which emits light evenly in all directions, then the light output is simply 4*pi lumen, since the solid angle of a sphere is 4*pi radians.

Similarly, if we have a 1 candela even light source which emits light only into a single hemisphere, and is dark on the other hemisphere (say an even emitter sitting against a wall), then the light output is 2*pi lumen, since we have the same intensity over half the solid angle.

For a right circular cone, with an planer angle at the vertex of A (the angle from one side of the cone to the other), the equation for the solid angle subtended by the cone is

<solid angle> = 2 * pi * ( 1 - cos(A/2) )

As you can check, this works out to 2pi for an angle A of 180 degrees (the hemisphere) and 4pi for an angle of 360 degrees (the full sphere)
</font><blockquote><font size="1" face="Verdana, Arial">code:</font><hr /><pre style="font-size:x-small; font-family: monospace;">
cone angle (degrees) solid angle (steradians)
0 0
10 0.024
20 0.095
30 0.214
60 0.841
90 1.84
180 6.28
360 12.57</pre><hr /></blockquote><font size="2" face="Verdana, Arial">So if you presume that the light is evenly distributed in a cone, and you know the angle of this cone, and you know the light's intensity in candela, you can determine the steradian value for that cone, multiply by the intensity, and get the light flux in lumen.

-Jon

 

[INRETECH]

Very good, brings back memories of Trig

Mike
www.inretech.com

 

[brightnorm]

Mike, Jonathan and Doug,

My math skills are long forgotten and you gentlemen are clearly knowledgeable.
So,

I repeat my question:

Isn't it also possible to multiply watts times the approximate watt/lumens efficiency ratio for a particular light source, whether incandescent or LED? Even though a very rough approximation, wouldn't it give at least a ballpark figure?

Please tell me if this has any validity.

Thanks,
Brightnorm

 

[Jonathan]

Originally posted by brightnorm:
Isn't it also possible to multiply watts times the approximate watt/lumens efficiency ratio for a particular light source, whether incandescent or LED? Even though a very rough approximation, wouldn't it give at least a ballpark figure?

<font size="2" face="Verdana, Arial">IMHO this approach has validity, but only if you accept that the ballpark is unusually large

That is how I came up with the 1 lumen 0.1 MSCP numbers in a previous post, and if someone came up with an actual measured value for a Nichia LED, and it was anything from 0.25 lumen to 2 lumen I feel that my estimate was 'pretty darn good'.

The reason that the ballpark needs to be so large is that the LEDs show quite a bit of variability in their lumen/watt output. Lumileds bins their superflux devices based on lumen output, and range that they allow for a bin is something like 100% to 150%, just so show how much variability there is.

-Jon

-Jon

 

[McGizmo]

I have a very scientific approach to the lumen output of the Nichia's

My guestimate is that a Nichia has a range of 1 to 1.5 lumens. I base this on two facts:

1) All Nichia white LED's (3 & 5 mm) use the same die; the epoxy envelope and focal length of the integrated lens is what varies.

2) SureFire claims 25 lumens come out of the KL2. This number would likely represent a median measure and is net of light loss within the bezel itself; it is likelyconservatively low. To get 25 lumens out of 19 LED's each LED should produce 1.3 Lumens.

I believe Jonathan is not only in the ballpark but likely in the infield

I really think we need to establish a universal measure of light output! My vote is for photons/fortenight (this will take into consideration the possibility of a *bad* day for the light source)

- Don ( personal friend of Mr. Science)

 

[Doug S]

Jonathan, you clearly have the best command of photometric units of those here that are willing to regularly [and patiently] post on the subject. Unfortunately illuminating/correcting the continuing photometric unit confusion that appears almost daily here seems akin to sweeping back the tide. I makes me wish that this BBS had some sort of FAQ archive that you could just reference each time FAQ worthy questions arise. It would be a good place to capture carefully crafted posts as yours above.

 

[N4aeq]

Thanks guys I was just trying to figure how many
leds I would need to equal a typical PR2 or 6
2-cell flashlight.
All the info is great & I will cut and paste it
to a file folder.

 

[dukeleto]

INRETECH, I sure would like to know where you got those 13,000 mcd 1° LEDs. Do you have a url?
Thanks

 

[brightnorm]

Originally posted by Jonathan:
</font><blockquote><font size="1" face="Verdana, Arial">quote:</font><hr /><font size="2" face="Verdana, Arial">Originally posted by brightnorm:
Isn't it also possible to multiply watts times the approximate watt/lumens efficiency ratio for a particular light source, whether incandescent or LED? Even though a very rough approximation, wouldn't it give at least a ballpark figure?

<font size="2" face="Verdana, Arial">IMHO this approach has validity, but only if you accept that the ballpark is unusually large.....</font><hr /></blockquote><font size="2" face="Verdana, Arial">Thanks Jon

BN

 

[ajaynejr]

I am aware of those facts, Candelas and Lumens are two different ways to measure brightness; but just as Lb and Kg are different ways to measure weight, we need a means to convert between them if only a crude formula

Do you mean "... just as Kg and psi (or Lb and KPa) are different ways to measure weight ..."

Just today I was shopping around for LCD light fixtures and I wanted to know the total light output. One fixture had a rating of 12000 mcd (millicandelas). The documentation did not say whether that was the output of each LED or to total of all of the LCDs, there were several. The documentation also did not say whether 12000 mcd was over a surface area of 1 square foot versus 100 square feet.

 

[Kitchen Panda]

Do you mean "... just as Kg and psi (or Lb and KPa) are different ways to measure weight ..."

Just today I was shopping around for LCD light fixtures and I wanted to know the total light output. One fixture had a rating of 12000 mcd (millicandelas). The documentation did not say whether that was the output of each LED or to total of all of the LCDs, there were several. The documentation also did not say whether 12000 mcd was over a surface area of 1 square foot versus 100 square feet.

You might notice that you're adding to a very old thread. Candelas and lumens measure different properties of light; candelas measure how concentrated the light is, and lumens measure the total amount of light. It's like an inch of water in the bottom of your glass vs. an inch of water in your basement!

Bill