Lumens. Lux, Candela
 

I am interested because I was looking at ultra-brite LEDS, and there
is all sorts of stuff quoted to give the usefulenss of these things,
mostly without the backing data to make it real.

OK. AFAICS. Please correct me or fine tune as necessary. If I am
pretty well right, then could somebody please simply say so G:

The CANDELA is the _unit_ of measure of emitted light from a source,
at the source.

The LUMEN is a measure of total light output. That is to say you
measure the CANDELAS, then assuming they are constant over the area of
light emitted (rare but for these purposes) then the LUMENs will be Cd
* area of emission. errr....no. There _is_ no area of emission from a
point source, at the source. OK. So it's the _angle_ over which the
light is emitted. How do you measure angle in three dimensions (bare
light globe), as distinct from a narrow beam or flat beam?

The LUX is a measure of light intensity, but measured at a distance
from a light source. Lumens/metre 2.

The CANDELLA would be the way to find out how bright the LED is at the
source. If the angle of emission is given also, then we trust we can
say that over that spread, we will se that brightness. A chart would
be nice. We could then approximate LUMENs (??)

BUT.

Then I get a site that gives the data for a LED-for-sale in LUX!!!
What does _that_ mean? No distance = no meaning AFAICS. The only thing
they did say was "Do not look into light source with remaining eye" or
words to that effect. This implies that this is collimated (sp?) to
almost lazer spread, and that therefore LUX could maybe be used, in
that LUX ~ Candela? WUP! No. It's a _wide angle_ LED!

The LED claims 1W , 3.6V 300mA 20 LUX, wide angle.

There is another site that has :
"LED-WHITE 5 mm SUPER-BRIGHT WHITE LED ~ 15 000 millicandela @ 20 mA,
+ or - 10 (20) degrees, VF @ 20 mA ~ 3.6 V, tolerance +/- 30%. Clear
Package"

I am having trouble getting more than a grunt out of the guy with the
15000 mCd LEd, either email or verbal.

BAH! I will try the other site.

So, I am assuming that one is the same intensity as the other (20
compared to 15) but for 1/20th the power. I have to assume that the
lower powered one is getting this from its narrower beam.

To add to that, Infrared LEDs are measured in Watts (or mW, and in one
case mW/sr.

So what is mW/sr?

Most spotlights are measured in Candlepower, which I gather is the
actual figure for the candelas emitted (as height is to metres).

So. If I have a LED with claimed Cd of 15000 mCd, or 15 Cd, then it is
a 15 CandlePower LED? Am I correct in comparing it with, say, a
spotlight with claimed output of 2,000,000 Candlepower? I realise
that:
- they are chalk and cheese (133,000 to one! G)
- I would have to look a the spread of the light in order to
compare, in that the luminous intensity at a given distance (LUX)
would be affected by that as well as Cd output.

I doubt this would (directly) affect the _visibility_ of the light
when looking at it from a distance in the dark. But it would certainly
affect its perceived brightness and ability as a source of
illumination.

Sorry for the ramble, but it is a bit messy.

************************************************** ** sorry
remove ns from my header address to reply via email

Spike....Spike? Hello?

Lumens. Lux, Candela
 

Hi, Nick. You have the right general ideas about lux, candela,
lumens. You can find more at my LED FAQ page:

http://www.pioneernet.net/optoeng/LED_FAQ.html

The latest LED technologies put out as much as a few 10s of lumens per
watt, but input power is usually limited to about 1/3 Watt or so per
LED. Compare that to a 50W halogen bulb (with its ~10 Lumens/Watt)
and you can begin to see why incandescents still have an advantage,
especially for spot lights.

LEDs are really at their best when you need colored light, since the
filter required to achieve colors with incandescents absorbs much of
their output.

If you need lots of lumens, it takes lots of LEDs. Those that have
the chip up close to the 'dome' spread their output over a broad angle
and vice versa. Broad angular coverage means less intensity and vice
versa. However, specs remain confused and confusing. The advice I
continue to give after some years at this is this: obtain some samples
and use your eyeballs to decide what works best.

Another excellent source of visible LED info:

http://members.misty.com/don/ledx.html

Paul Mathews

Old Nick wrote in message . ..
I am interested because I was looking at ultra-brite LEDS, and there
is all sorts of stuff quoted to give the usefulenss of these things,
mostly without the backing data to make it real.

OK. AFAICS. Please correct me or fine tune as necessary. If I am
pretty well right, then could somebody please simply say so G:

The CANDELA is the _unit_ of measure of emitted light from a source,
at the source.

The LUMEN is a measure of total light output. That is to say you
measure the CANDELAS, then assuming they are constant over the area of
light emitted (rare but for these purposes) then the LUMENs will be Cd
* area of emission. errr....no. There _is_ no area of emission from a
point source, at the source. OK. So it's the _angle_ over which the
light is emitted. How do you measure angle in three dimensions (bare
light globe), as distinct from a narrow beam or flat beam?

The LUX is a measure of light intensity, but measured at a distance
from a light source. Lumens/metre 2.

The CANDELLA would be the way to find out how bright the LED is at the
source. If the angle of emission is given also, then we trust we can
say that over that spread, we will se that brightness. A chart would
be nice. We could then approximate LUMENs (??)

BUT.

Then I get a site that gives the data for a LED-for-sale in LUX!!!
What does _that_ mean? No distance = no meaning AFAICS. The only thing
they did say was "Do not look into light source with remaining eye" or
words to that effect. This implies that this is collimated (sp?) to
almost lazer spread, and that therefore LUX could maybe be used, in
that LUX ~ Candela? WUP! No. It's a _wide angle_ LED!

The LED claims 1W , 3.6V 300mA 20 LUX, wide angle.

There is another site that has :
"LED-WHITE 5 mm SUPER-BRIGHT WHITE LED ~ 15 000 millicandela @ 20 mA,
+ or - 10 (20) degrees, VF @ 20 mA ~ 3.6 V, tolerance +/- 30%. Clear
Package"

I am having trouble getting more than a grunt out of the guy with the
15000 mCd LEd, either email or verbal.

BAH! I will try the other site.

So, I am assuming that one is the same intensity as the other (20
compared to 15) but for 1/20th the power. I have to assume that the
lower powered one is getting this from its narrower beam.

To add to that, Infrared LEDs are measured in Watts (or mW, and in one
case mW/sr.

So what is mW/sr?

Most spotlights are measured in Candlepower, which I gather is the
actual figure for the candelas emitted (as height is to metres).

So. If I have a LED with claimed Cd of 15000 mCd, or 15 Cd, then it is
a 15 CandlePower LED? Am I correct in comparing it with, say, a
spotlight with claimed output of 2,000,000 Candlepower? I realise
that:
- they are chalk and cheese (133,000 to one! G)
- I would have to look a the spread of the light in order to
compare, in that the luminous intensity at a given distance (LUX)
would be affected by that as well as Cd output.

I doubt this would (directly) affect the _visibility_ of the light
when looking at it from a distance in the dark. But it would certainly
affect its perceived brightness and ability as a source of
illumination.

Sorry for the ramble, but it is a bit messy.

************************************************** ** sorry
remove ns from my header address to reply via email

Spike....Spike? Hello?

Lumens. Lux, Candela
 

Subject

By definition:

1 Candella per square foot equals 1 foot candle.

After that it was considered too dangerous to try and teach anything else to
a lighting salesman.

HTH


--
Lew

S/A: Challenge, The Bullet Proof Boat, (Under Construction in the Southland)
Visit: http://home.earthlink.net/~lewhodgett for Pictures

Lumens. Lux, Candela
 

On Fri, 30 Jan 2004 19:53:38 +0800, Old Nick
vaguely proposed a theory
.......and in reply I say!:

Actually I have been reading while I wait G

Here is an interesting page http://www.misty.com/people/don/ledx.html
and a rather inflammatory quote from it:


I admoit that paras two and three are reveresed to emphasise the
surprising facts.

"Why LEDs can be 10 times as efficient as incandescents in some
applications but not in general home lighting!
UPDATED slightly 1/13/2004.
First, the figures:

The better usual modern white LEDs (as of January 2004) produce about
17-25 lumens of light per watt of electricity delivered to the LEDs
when the LEDs are supplied "typical" current or that at which their
characteristics are specified. Maybe just a little more for the
highest ranks/binnings. Most such white LEDs will be slightly more
efficient when moderately underpowered and will be less efficient when
overpowered.

Compare to 14-17.5 lumens per watt for standard "A19" 120 volt 60 to
100 watt incandescents, and typically 16 to 21 for most halogen lamps
rated to last 2,000 hours or more.

As for the near-future, Nichia claims that white LEDs that achieve 60
lumens/watt will go into production in 2005. Cree has achieved 65
lumens per watt in laboratory prototypes using industry standard
packaging and 74 lumens per watt with special packaging, and has
announced a product line (blue LED dice/"chips" usable for such white
LEDs). More in my bright/efficient LED page, updated 1/13/2004."






I am interested because I was looking at ultra-brite LEDS, and there
is all sorts of stuff quoted to give the usefulenss of these things,
mostly without the backing data to make it real.

OK. AFAICS. Please correct me or fine tune as necessary. If I am
pretty well right, then could somebody please simply say so G:

The CANDELA is the _unit_ of measure of emitted light from a source,
at the source.

The LUMEN is a measure of total light output. That is to say you
measure the CANDELAS, then assuming they are constant over the area of
light emitted (rare but for these purposes) then the LUMENs will be Cd
* area of emission. errr....no. There _is_ no area of emission from a
point source, at the source. OK. So it's the _angle_ over which the
light is emitted. How do you measure angle in three dimensions (bare
light globe), as distinct from a narrow beam or flat beam?

The LUX is a measure of light intensity, but measured at a distance
from a light source. Lumens/metre 2.

The CANDELLA would be the way to find out how bright the LED is at the
source. If the angle of emission is given also, then we trust we can
say that over that spread, we will se that brightness. A chart would
be nice. We could then approximate LUMENs (??)

BUT.

Then I get a site that gives the data for a LED-for-sale in LUX!!!
What does _that_ mean? No distance = no meaning AFAICS. The only thing
they did say was "Do not look into light source with remaining eye" or
words to that effect. This implies that this is collimated (sp?) to
almost lazer spread, and that therefore LUX could maybe be used, in
that LUX ~ Candela? WUP! No. It's a _wide angle_ LED!

The LED claims 1W , 3.6V 300mA 20 LUX, wide angle.

There is another site that has :
"LED-WHITE 5 mm SUPER-BRIGHT WHITE LED ~ 15 000 millicandela @ 20 mA,
+ or - 10 (20) degrees, VF @ 20 mA ~ 3.6 V, tolerance +/- 30%. Clear
Package"

I am having trouble getting more than a grunt out of the guy with the
15000 mCd LEd, either email or verbal.

BAH! I will try the other site.

So, I am assuming that one is the same intensity as the other (20
compared to 15) but for 1/20th the power. I have to assume that the
lower powered one is getting this from its narrower beam.

To add to that, Infrared LEDs are measured in Watts (or mW, and in one
case mW/sr.

So what is mW/sr?

Most spotlights are measured in Candlepower, which I gather is the
actual figure for the candelas emitted (as height is to metres).

So. If I have a LED with claimed Cd of 15000 mCd, or 15 Cd, then it is
a 15 CandlePower LED? Am I correct in comparing it with, say, a
spotlight with claimed output of 2,000,000 Candlepower? I realise
that:
- they are chalk and cheese (133,000 to one! G)
- I would have to look a the spread of the light in order to
compare, in that the luminous intensity at a given distance (LUX)
would be affected by that as well as Cd output.

I doubt this would (directly) affect the _visibility_ of the light
when looking at it from a distance in the dark. But it would certainly
affect its perceived brightness and ability as a source of
illumination.

Sorry for the ramble, but it is a bit messy.

************************************************* *** sorry
remove ns from my header address to reply via email

Spike....Spike? Hello?

************************************************** ** sorry
remove ns from my header address to reply via email

Spike....Spike? Hello?

Lumens. Lux, Candela
 

I lifted this eight year old archived post from Andrei Broder
who says it still simply, but without those fuzzy edges

From: "Andrei Broder"
Date: Mon, 05 Feb 96 00:47:45 -0800
--------------------------------------------------------------------------------


Light flux is measured in lumens. Light sources are often labeled
with an output rating in lumens. //

Lumen is actually a "derived unit". The basic international unit,
measures luminous intensity and is called candela. Candles and
candlepower are the same thing but these are deprecated names. It
tells how much flux is flowing through a solid angle,
which is measured in steradians. A point source that has intensity
of one candle puts out a lumen per steradian. A unit area, all at
unit distance from a point covers exactly a steradian.

Illumination (illuminance) is the area density of incident luminous
flux: how many lumens per unit area. A lux is one lumen per one
square meter. Illumination from a point source falls off as the
square of the distance. So if you divide the intensity of a point
source in candles by the distance from it in meters squared, you
have the illumination in lux at that distance. (Remember this
assumes a single point source in a sphere - no reflectors, lenses,
etc. What we have are often multiple complex sources.)

Read the rec.photo FAQ for a good intro to all this. I cribbed from
it.
##########################################

Brian W

On Fri, 30 Jan 2004 19:53:38 +0800, Old Nick
wrote:

I am interested because I was looking at ultra-brite LEDS, and there
is all sorts of stuff quoted to give the usefulenss of these things,
mostly without the backing data to make it real.

OK. AFAICS. Please correct me or fine tune as necessary. If I am
pretty well right, then could somebody please simply say so G:

The CANDELA is the _unit_ of measure of emitted light from a source,
at the source.

The LUMEN is a measure of total light output. That is to say you
measure the CANDELAS, then assuming they are constant over the area of
light emitted (rare but for these purposes) then the LUMENs will be Cd
* area of emission. errr....no. There _is_ no area of emission from a
point source, at the source. OK. So it's the _angle_ over which the
light is emitted. How do you measure angle in three dimensions (bare
light globe), as distinct from a narrow beam or flat beam?

The LUX is a measure of light intensity, but measured at a distance
from a light source. Lumens/metre 2.

The CANDELLA would be the way to find out how bright the LED is at the
source. If the angle of emission is given also, then we trust we can
say that over that spread, we will se that brightness. A chart would
be nice. We could then approximate LUMENs (??)

BUT.

Then I get a site that gives the data for a LED-for-sale in LUX!!!
What does _that_ mean? No distance = no meaning AFAICS. The only thing
they did say was "Do not look into light source with remaining eye" or
words to that effect. This implies that this is collimated (sp?) to
almost lazer spread, and that therefore LUX could maybe be used, in
that LUX ~ Candela? WUP! No. It's a _wide angle_ LED!

The LED claims 1W , 3.6V 300mA 20 LUX, wide angle.

There is another site that has :
"LED-WHITE 5 mm SUPER-BRIGHT WHITE LED ~ 15 000 millicandela @ 20 mA,
+ or - 10 (20) degrees, VF @ 20 mA ~ 3.6 V, tolerance +/- 30%. Clear
Package"

I am having trouble getting more than a grunt out of the guy with the
15000 mCd LEd, either email or verbal.

BAH! I will try the other site.

So, I am assuming that one is the same intensity as the other (20
compared to 15) but for 1/20th the power. I have to assume that the
lower powered one is getting this from its narrower beam.

To add to that, Infrared LEDs are measured in Watts (or mW, and in one
case mW/sr.

So what is mW/sr?

Most spotlights are measured in Candlepower, which I gather is the
actual figure for the candelas emitted (as height is to metres).

So. If I have a LED with claimed Cd of 15000 mCd, or 15 Cd, then it is
a 15 CandlePower LED? Am I correct in comparing it with, say, a
spotlight with claimed output of 2,000,000 Candlepower? I realise
that:
- they are chalk and cheese (133,000 to one! G)
- I would have to look a the spread of the light in order to
compare, in that the luminous intensity at a given distance (LUX)
would be affected by that as well as Cd output.

I doubt this would (directly) affect the _visibility_ of the light
when looking at it from a distance in the dark. But it would certainly
affect its perceived brightness and ability as a source of
illumination.

Sorry for the ramble, but it is a bit messy.

************************************************* *** sorry
remove ns from my header address to reply via email

Spike....Spike? Hello?

Lumens. Lux, Candela
 

On 30 Jan 2004 11:05:59 -0800, (Paul Mathews)
vaguely proposed a theory
.......and in reply I say!:

Hi, Nick. You have the right general ideas about lux, candela,
lumens. You can find more at my LED FAQ page:

http://www.pioneernet.net/optoeng/LED_FAQ.html

OK. I will check that out for sure.


The latest LED technologies put out as much as a few 10s of lumens per
watt, but input power is usually limited to about 1/3 Watt or so per
LED. Compare that to a 50W halogen bulb (with its ~10 Lumens/Watt)
and you can begin to see why incandescents still have an advantage,
especially for spot lights.

LEDs are really at their best when you need colored light, since the
filter required to achieve colors with incandescents absorbs much of
their output.


I could see the difference. It was just that with the way LEDs were
being written up, I was wondering if I was actually comparing apples
with apples at all.

If you need lots of lumens, it takes lots of LEDs. Those that have
the chip up close to the 'dome' spread their output over a broad angle
and vice versa. Broad angular coverage means less intensity and vice
versa.

However, specs remain confused and confusing.

Ah! Good! At least it's not just being dumb again. :-

The advice I
continue to give after some years at this is this: obtain some samples
and use your eyeballs to decide what works best.

Hah! Trouble is some of these places want to sell you 20 at a time. IN
Oz, at $4 each, an experiment can get pretty expensive.


Another excellent source of visible LED info:

http://members.misty.com/don/ledx.html

See my later post on this thread. Thanks

************************************************** ** sorry
remove ns from my header address to reply via email

Spike....Spike? Hello?

Lumens. Lux, Candela
 

On Fri, 30 Jan 2004 19:12:58 GMT, "Lew Hodgett"
vaguely proposed a theory
.......and in reply I say!:

Subject

By definition:

1 Candella per square foot equals 1 foot candle.

After that it was considered too dangerous to try and teach anything else to
a lighting salesman.

HTH

It does. Now I feel a bit better about where the problem lies with all
this info G

************************************************** ** sorry
remove ns from my header address to reply via email

Spike....Spike? Hello?

Lumens. Lux, Candela
 

On Sat, 31 Jan 2004 00:53:38 GMT, Brian Whatcott
vaguely proposed a theory
.......and in reply I say!:

Well for a _start_, I at least now know what an sr is ..Thank you.


I lifted this eight year old archived post from Andrei Broder
who says it still simply, but without those fuzzy edges

From: "Andrei Broder"
Date: Mon, 05 Feb 96 00:47:45 -0800
--------------------------------------------------------------------------------


************************************************** ** sorry
remove ns from my header address to reply via email

Spike....Spike? Hello?

Lumens. Lux, Candela
 

I've had very good luck purchasing blue and white LEDs from an ebay
seller in Hong Kong. He ships everywhere for a fixed price. Very
reasonable. There's an electronics/parts/LEDs category on ebay, so it
should be easy to find the source.

Paul Mathews

Old Nick wrote in message . ..
On 30 Jan 2004 11:05:59 -0800, (Paul Mathews)
vaguely proposed a theory
......and in reply I say!:

Hi, Nick. You have the right general ideas about lux, candela,
lumens. You can find more at my LED FAQ page:

http://www.pioneernet.net/optoeng/LED_FAQ.html

OK. I will check that out for sure.


The latest LED technologies put out as much as a few 10s of lumens per
watt, but input power is usually limited to about 1/3 Watt or so per
LED. Compare that to a 50W halogen bulb (with its ~10 Lumens/Watt)
and you can begin to see why incandescents still have an advantage,
especially for spot lights.

LEDs are really at their best when you need colored light, since the
filter required to achieve colors with incandescents absorbs much of
their output.


I could see the difference. It was just that with the way LEDs were
being written up, I was wondering if I was actually comparing apples
with apples at all.

If you need lots of lumens, it takes lots of LEDs. Those that have
the chip up close to the 'dome' spread their output over a broad angle
and vice versa. Broad angular coverage means less intensity and vice
versa.

However, specs remain confused and confusing.

Ah! Good! At least it's not just being dumb again. :-

The advice I
continue to give after some years at this is this: obtain some samples
and use your eyeballs to decide what works best.

Hah! Trouble is some of these places want to sell you 20 at a time. IN
Oz, at $4 each, an experiment can get pretty expensive.


Another excellent source of visible LED info:

http://members.misty.com/don/ledx.html

See my later post on this thread. Thanks

************************************************** ** sorry
remove ns from my header address to reply via email

Spike....Spike? Hello?

Lumens. Lux, Candela
 

Nigel Calder has an extremely good article on
new marine lighting technology in the latest
issue of "Professional Boatbuilder" magazine.
One of his goals is to compare the utility of
various technologies for various tasks. Doing
this is tricky, but he spends a lot of time
explaining the units involved so that one can
at least understand why oranges and apples
are not directly comparable. he also spends
some time comparing efficacy of light sources
(pretty much "efficiency" if you mean "light
output per watt").

anyway, it's great Calder writing, remarkably
well-done research, and boiled-down so that
one can come away with some understanding
of the "shape" of the problem space.

as for ProBoat, if you are really interested
in boats, even if you don't intend to build
one yourself, i recommend it most highly.
it costs a few bucks, but is full of information
you won't find anywhere else and written by
people who really understand their stuff.

-mo