High Efficiency White LEDs

[JohnR66]

After trying a couple Cree XR-E based flashlights, I must say I'm impressed.
I've heard way over 100 lumens per watt designs operating in the labs
several months ago by various manufacturers, but nothing of late. Anyone got
the inside scoop?

As for the XR-E LEDs, I'm aware the efficiency drops due to operating die
temps, but even so, the l/w figures seem to remain in the upper range of
CFLs (50-70 range).

John

 

[Victor Roberts]

After trying a couple Cree XR-E based flashlights, I must say I'm impressed.
I've heard way over 100 lumens per watt designs operating in the labs
several months ago by various manufacturers, but nothing of late. Anyone got
the inside scoop?

Cree was bragging about 131 lm/W from a low power LED, and
last week at LS:11 Nichia was bragging about one over 150
lm/W. However, these are all at a junction temp of 25C
which cannot be achieved without a refrigerated heat sink,
and they are not power devices, which are less efficient.

As for the XR-E LEDs, I'm aware the efficiency drops due to operating die
temps, but even so, the l/w figures seem to remain in the upper range of
CFLs (50-70 range).

In my mind, the more important question is what is the
minimum guaranteed efficacy of a LED that a person can
actually buy, measured at a junction temperature that can be
achieved in a real application. Last time I checked, about
6 months ago, the answer was "about 40 lm/W" and at a cost
per lumen that was at least 10 times that of a CFL.

BTW- I learned at LS:11 that the LED manufacturers are well
aware that they could solve white LED color issues by using
UV instead of blue LEDs as the pump, but they don't want to
take the Stokes Shift hit to the efficacy.

--
Vic Roberts
http://www.RobertsResearchInc.com
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[JohnR66]

Cree was bragging about 131 lm/W from a low power LED, and
last week at LS:11 Nichia was bragging about one over 150
lm/W. However, these are all at a junction temp of 25C
which cannot be achieved without a refrigerated heat sink,
and they are not power devices, which are less efficient.


In my mind, the more important question is what is the
minimum guaranteed efficacy of a LED that a person can
actually buy, measured at a junction temperature that can be
achieved in a real application. Last time I checked, about
6 months ago, the answer was "about 40 lm/W" and at a cost
per lumen that was at least 10 times that of a CFL.

BTW- I learned at LS:11 that the LED manufacturers are well
aware that they could solve white LED color issues by using
UV instead of blue LEDs as the pump, but they don't want to
take the Stokes Shift hit to the efficacy.

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
site without written permission.

The next few years should prove interesting. The current most efficient LEDs
are ideal for portable lighting. They do have a ways to go for general
lighting where price, CRIs and color temp are more of importance.
John

 

[Victor Roberts]

The next few years should prove interesting. The current most efficient LEDs
are ideal for portable lighting. They do have a ways to go for general
lighting where price, CRIs and color temp are more of importance.
John

I agree that there are a number of applications where LEDs
are an ideal light source. These include any type of
colored indicator lamp, and low lumen directed light
applications, such as flashlights and task lamps.

However, data available from the US DOE states that 98% of
the lighting energy in this country is used by high lumen
white light sources. My primary interest is in energy
conservation. LEDs will not reduce lighting energy
consumption in the US until they are more efficient than
linear fluorescent lamps and metal halide lamps and their
cost per lumen has dropped to a level consistent with their
efficacy and life advantage over these existing light
sources.

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
site without written permission.

 

[TKM]

I agree that there are a number of applications where LEDs
are an ideal light source. These include any type of
colored indicator lamp, and low lumen directed light
applications, such as flashlights and task lamps.

However, data available from the US DOE states that 98% of
the lighting energy in this country is used by high lumen
white light sources. My primary interest is in energy
conservation. LEDs will not reduce lighting energy
consumption in the US until they are more efficient than
linear fluorescent lamps and metal halide lamps and their
cost per lumen has dropped to a level consistent with their
efficacy and life advantage over these existing light
sources.

While I agree with Vic overall, there are some white light applications
where the use of LEDs will result in energy savings now. I'm working with
the Am. Lighting Association and several other groups to identify others.
We're using "application efficiency" as the metric or, roughly, the watts
required for suitable illumination of the task involved and we realize that
such a a definition is subject to passionate interpretation.

But, we think the use of easily-available state-of-the art LEDs for the
following would result in energy savings: portable task lights, residential
under-counter and in-furniture lights, step lights, and other outdoor and
landscape lighting applications. I've just ordered the parts for an
all-LED landscape lighting project, so check back in late July for a report.

Terry McGowan

 

[Victor Roberts]

While I agree with Vic overall, there are some white light applications
where the use of LEDs will result in energy savings now. I'm working with
the Am. Lighting Association and several other groups to identify others.
We're using "application efficiency" as the metric or, roughly, the watts
required for suitable illumination of the task involved and we realize that
such a a definition is subject to passionate interpretation.

But, we think the use of easily-available state-of-the art LEDs for the
following would result in energy savings: portable task lights, residential
under-counter and in-furniture lights, step lights, and other outdoor and
landscape lighting applications. I've just ordered the parts for an
all-LED landscape lighting project, so check back in late July for a report.

Terry - I agree that the directional nature of LEDs should
be taken into account and I should have included that in my
statement about "more efficient". I do endorse
"application efficacy" and agree that there are still
multiple definitions for this metric - we even use different
names

As for the applications you mention, I agree they are all
potentially good applications for LEDs, but fail to address
those applications where we use 98% of lighting energy in
the US.

--
Vic Roberts
http://www.RobertsResearchInc.com
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This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
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