Clarifications for led intensity measurements...

[KILOWATT]

Hi fellow hobbyists (and professionals!) ;-).
I'm on the net since may 2000 and just started to discover Ebay a few days
ago...serious! There's some interesting components i can't find in
stores in Montréal...espacially good deals on leds. Because of the newer
high-powered white leds availability, it's more and more interesting to
consider them for lighting requirements. To go to the point, some are
specified in microcandelas while most high powered ones are specified in
lumens (here's an nice high power one)
http://cgi.ebay.ca/ws/eBayISAPI.dll?ViewItem&category=66952&item=3868725654&
rd=1

Anyone here have an interesting link where i can find conversion/equivalence
charts to allow me to better understand those units im not very familiar
with. TIA for any replies

--
Alain(alias:Kilowatt)
Montréal Québec
PS: 1000 excuses for errors or omissions,
i'm a "pure" french canadian!
Come to visit me at: http://kilowatt.camarades.com
(If replying also by e-mail, remove
"no spam" from the adress.)

 

[Fritz Schlunder]

Hi fellow hobbyists (and professionals!) ;-).
I'm on the net since may 2000 and just started to discover Ebay a few days
ago...serious! There's some interesting components i can't find in
stores in Montréal...espacially good deals on leds. Because of the newer
high-powered white leds availability, it's more and more interesting to
consider them for lighting requirements. To go to the point, some are
specified in microcandelas while most high powered ones are specified in
lumens (here's an nice high power one)
http://cgi.ebay.ca/ws/eBayISAPI.dll?ViewItem&category=66952&item=3868725654&
rd=1

Anyone here have an interesting link where i can find conversion/equivalence
charts to allow me to better understand those units im not very familiar
with. TIA for any replies

The very bottom of this part of Don Klipstein's website talks a little about
this:

http://members.misty.com/don/led.html#lc

Candelas are a measure of luminous intensity, while lumens are a measure of
luminous flux. They are not equivalent, but they are related. If you stare
into a laser pointer beam you will find that it has extremely high luminous
intensity (candelas). On the other hand if you try to light up a whole room
with the laser pointer you will find that it does a very poor job (total
lumens or total light output is very low). If you stare straight at a
standard bare 60W incandescent lamp you will find that it has a lower
luminous intensity (candela rating) than the laser pointer. On the other
hand, the 60W lamp produces vastly more lumens, so it will light up a whole
room much more effectively than the laser pointer.

If you want to make a very intense spotlight you will want LEDs with high
luminous intensity (high candela ratings). If you don't really care about a
bright spot, but want overall bright floodlighting of a whole room you will
want LEDs with very high lumen ratings.

Lumens are an interesting unit because they at least try to take into
account the effects of human eye sensitivity. Human eyes are vastly more
sensitive to green light than to blue and red light. A 100 lumen green
light should in theory light up a room to approximately the same overall
effective brightness (as perceived by a human) as a 100 lumen blue or red
light.

 

[KILOWATT]

Thanks a lot Fritz for your very informative reply...was appreciated.
I discovered that i was wrong with units... millicandelas stand
for"mcd"...not microcandelas! ;-) Since my OP, i've dicovered this
interesting site that many are (you?) aware of:
http://ledmuseum.home.att.net
Thanks again and for any future replies

--
Alain(alias:Kilowatt)
Montréal Québec
PS: 1000 excuses for errors or omissions,
i'm a "pure" french canadian!
Come to visit me at: http://kilowatt.camarades.com
(If replying also by e-mail, remove
"no spam" from the adress.)

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

Hi fellow hobbyists (and professionals!) ;-).
I'm on the net since may 2000 and just started to discover Ebay a few days
ago...serious! There's some interesting components i can't find in
stores in Montréal...espacially good deals on leds. Because of the newer
high-powered white leds availability, it's more and more interesting to
consider them for lighting requirements. To go to the point, some are
specified in microcandelas while most high powered ones are specified in
lumens (here's an nice high power one)
http://cgi.ebay.ca/ws/eBayISAPI.dll?ViewItem&category=66952&item=3868725
654&
rd=1

Anyone here have an interesting link where i can find conversion/equivalence
charts to allow me to better understand those units im not very familiar
with. TIA for any replies

Here's what your auction says about the LEDs:

Why LEDs?

* Last an average of 100,000 hours (or about ten years).

My experience with the cheap Hong Kong LEDs that I've been running 24/7
is that, depending on the current, they last less than 1/10 that figure.
If I run the LEDs at 20 mA, they might last for 6 months before the
light decreases to less than half.

* Withstand shocks, vibrations, frequent switching and temperature

extremes that rapidly incapacitate fragile incandescent lamps

There's nothing hotter than a tungsten filament, so this is just
advertising hype.

* Are 10 to 50 times more energy-efficient, thus reducing your

operating costs by up to 90%.

LEDs are little, if any, more efficient than incandescent lamps. Read
Don Klipstein's LED pages for the truth.
http://members.misty.com/don/ledx.html

 

[Fritz Schlunder]

Here's what your auction says about the LEDs:



My experience with the cheap Hong Kong LEDs that I've been running 24/7
is that, depending on the current, they last less than 1/10 that figure.
If I run the LEDs at 20 mA, they might last for 6 months before the
light decreases to less than half.

Even at 10,000 hours that is still dramatically better than a comparably
sized incandescant lamp. Many incandescant flashlight lamps have rated
lifetimes of something on the order of 15 hours, or 40 hours, or maybe a
couple of hundred (it varies allot). Light output of incandescant lamps
also decrease significantly with usage as well.

extremes that rapidly incapacitate fragile incandescent lamps

There's nothing hotter than a tungsten filament, so this is just
advertising hype.

So a tungsten filament runs hotter. Yeah, so. LEDs are far more immune to
physical shock than incandescant lamps, so the manufacturer isn't in any way
lieing about their product here. It is true.

operating costs by up to 90%.

LEDs are little, if any, more efficient than incandescent lamps. Read
Don Klipstein's LED pages for the truth.
http://members.misty.com/don/ledx.html

Claiming 10-50 times energy efficiency is of course most fanciful (except of
course in the case of colored light sources). The particular LEDs the OP
linked to have a luminous efficacy of around 25 lumens/watt. Small
incandescent flashlight lamps have bad luminous efficacy, perhaps in the
neighborhood of 6 lumens/watt. This does represent over four times the
efficiency when used as a flashlight replacement. Combined with the LED's
other advantages such as dramatically longer life, built in optics/reflector
(external ones optional, but for incandescent they are required and further
reduce the already low luminous efficacy), ability to be rapidly modulated,
dimming ability (without major loss of efficiency), etc., LEDs are really
much more versatile and superior to incandescent lamps in a vast number of
applications.

Comparing a little 0.5W LED's luminous efficacy to a large 120V 500W halogen
isn't really very fair. Even so the LED's 25 lumens/watt is still a bit
better than the 21 lumens/watt or so for a typical large halogen. Compared
to a typical 60W non-halogen long life lamp (long meaning 1000 hours)
operated at 120V the LEDs excel even more since such an incandescent might
only achieve 14 lumens/watt. In high voltage (240V) countries the luminous
efficacy and durability/mechanical shock resistance of the incandescent is
even worse.

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

in message

Even at 10,000 hours that is still dramatically better than a comparably
sized incandescant lamp. Many incandescant flashlight lamps have rated
lifetimes of something on the order of 15 hours, or 40 hours, or maybe a
couple of hundred (it varies allot). Light output of incandescant lamps
also decrease significantly with usage as well.

Some submini incandescents are rated for over ten thousand hours.

So a tungsten filament runs hotter. Yeah, so. LEDs are far more immune to
physical shock than incandescant lamps, so the manufacturer isn't in any way
lieing about their product here. It is true.

It is _not_ true that LEDs will handle heat better than an incandescent,
as the ad implied.

operating costs by up to 90%.

LEDs are little, if any, more efficient than incandescent lamps. Read
Don Klipstein's LED pages for the truth.
http://members.misty.com/don/ledx.html

[snip]

 

[Fritz Schlunder]

Some submini incandescents are rated for over ten thousand hours.

Unfortunately at less than something like three lumens per watt.

It is _not_ true that LEDs will handle heat better than an incandescent,
as the ad implied.

Oh right. Yeah I glossed over that part of their statement. Yeah LEDs
don't handle temperature extremes better than incandescent. In fact they
handle high temperatures much worse, while low temperature extremes are
pretty immaterial since neither have any problems with any reasonably low
temperature.