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Lumileds 115 lm/W Power White LED

V

Victor Roberts

Jan 1, 1970
0
DigiTimes.com is reporting that Lumileds has reported a
record 115 lm/W for a white power LED.

A device operating at 350 mA and drawing 1.2 Watts generated
136 lumens of white light at a CCT of 4865K. 136 lm divided
by 1.2 Watts gives 113 lm/W but the story states 115 lm/W so
there must be some small round-off errors. The CRI is not
given and I can't find any information about this LED on the
Lumileds web site.

This is much better IMHO than the 131 lm/W reported by Cree
last June since the Cree device was a very small, low power
LED not suitable for general lighting applications.

All the normal caveats apply. This was most certainly
measured at a junction temperature of 25C, is certainly the
best device they have produced to date instead of typical
data for the batch and may even be an unpackaged chip.
However, this is still outstanding performance, and the
performance should remain quite good even with when the
junction temperature is at a more reasonable steady state
value.

I'm looking forward to the announcement of products that
include the new technologies that made this achievement
possible

I'll be attending the DOE's annual LED Workshop next week in
Phoenix. Hopefully we will learn more about this device at
that meeting.

--
Vic Roberts
http://www.RobertsResearchInc.com
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V

Victor Roberts

Jan 1, 1970
0
And cree gets 100lm/W with actual shipping devices - maybe a little
more, at 20mA, substantially underdriving.

In shipping devices, you can get bins from Cree up to 90lm/W or so at
the moment, in volume.

Have you tried to buy 90 lm/W LEDs from Cree? Note that you
must order LEDs from at least two efficacy bins, and Cree
does NOT guarantee the distribution of LEDs between those
two bins (all can be in the lower efficacy bin) and
certainly does not guarantee the distribution of performance
within a bin.

[snip]

--
Vic Roberts
http://www.RobertsResearchInc.com
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T

TKM

Jan 1, 1970
0
Ian Stirling said:
And cree gets 100lm/W with actual shipping devices - maybe a little
more, at 20mA, substantially underdriving.

In shipping devices, you can get bins from Cree up to 90lm/W or so at
the moment, in volume.

It'll be interesting to see how this round of vapourware and product
improvements turn out.
I would't be astonished to see 150lm/W by mid 2008, with 100lm/W devices
falling a little in price.

It would be interesting to know where the improved lpw performance is coming
from -- better extraction efficiency, material purity conbtrol, mounting
geometry, etc. Anything stand out or is it a combination of factors?

Terry McGowan
 
V

Victor Roberts

Jan 1, 1970
0
It would be interesting to know where the improved lpw performance is coming
from -- better extraction efficiency, material purity conbtrol, mounting
geometry, etc. Anything stand out or is it a combination of factors?

Terry McGowan

I think most of the recent gain comes from improvements in
light extraction efficiency.

--
Vic Roberts
http://www.RobertsResearchInc.com
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D

Don Klipstein

Jan 1, 1970
0
Victor Roberts said:
I think most of the recent gain comes from improvements in
light extraction efficiency.

I have noticed extraction efficiency being talked about, to an extent
where I suspect that materials improvements have been downplayed.

It appears to me that a big extraction problem was from photons
generated inside the LED chip experiencing total internal reflection at
the surface of some layer of the chip due to high refractive index of the
photon-producing semiconductor. Back when I heard more as to how
extraction efficiency was being improved, the ways mentioned for fixing
this were texturing surfaces to reduce total internal reflection losses,
and making funny shaped chips (such as truncated inverted pyramid, used by
Lumileds in many red, orange and yellow/amber devices for a few years
already).

It appears to me that there are now better phosphors, especially for the
laboratory prototypes announced within the past half-year or so but also
for one line of production units that became available last year. I
noticed color temperatures dropping from near-6000 in these to 5,000's and
4,000's. Since the phosphor output has more lumens per watt of output
than blue LED light has, even after the Stokes loss, luminous efficacy of
a white LED should be improved by adding more phosphor. Yet, in most
cases the "warm white version" has less efficacy than the version with a
usual higher color temperature. Whatever problem is involved with
thicker layers of phosphor or more concentrated phosphor could be being
solved given recent efficacy highs being associated with color
temperatures lower than what I consider usual for white LEDs.

Somehow I suspect some would call a phosphor loss due to absorption or
other blockage an "extraction" issue.

However, I have noticed the "wallplug efficiencies" of recent high
efficacy white LEDs (a couple of which I have) to exceed those of any blue
ones I ever had my hands on. Maybe the really good blue ones got better
but the really good blue chips are being used to make white LEDs?

Another thing I noticed in the past year or two: Some trend of the peak
wavelength of the "blue peak" in the spectra of white LEDs getting a
little shorter in wavelength. I see two advantages to this and a possible
little downside:

1) Greater percentage of output can be from phosphor for same CCT and
efficacy can be increased, since 450 nm has greater "blue efficacy" than
470 nm

2) The color is a little less greenish, allowing a more phosphor-
dominated lower-CCT color (with more lumens per output watt) without
getting noticeably more greenish than "blackbody".

Downside: Lower scotopic/photopic ratio. In applications where scotopic
vision is significant, such as nightlights, camping lanterns, some outdoor
lighting and some usage of some flashlights, improvement in illumination
ability will be less than the improvement in photometric performance -
although I see improvement still advancing.
However, I do not consider this a big issue, especially since in most
room lighting scotopic vision has a significance at most to an extent
that is a subject of controversy.

- Don Klipstein ([email protected])
 
V

Victor Roberts

Jan 1, 1970
0
I have noticed extraction efficiency being talked about, to an extent
where I suspect that materials improvements have been downplayed.

It appears to me that a big extraction problem was from photons
generated inside the LED chip experiencing total internal reflection at
the surface of some layer of the chip due to high refractive index of the
photon-producing semiconductor. Back when I heard more as to how
extraction efficiency was being improved, the ways mentioned for fixing
this were texturing surfaces to reduce total internal reflection losses,
and making funny shaped chips (such as truncated inverted pyramid, used by
Lumileds in many red, orange and yellow/amber devices for a few years
already).

That is also my understanding. The higher extraction
efficiency is achieved through the use of surface patterning
of one type of another to reduce internal reflection.
It appears to me that there are now better phosphors, especially for the
laboratory prototypes announced within the past half-year or so but also
for one line of production units that became available last year. I
noticed color temperatures dropping from near-6000 in these to 5,000's and
4,000's. Since the phosphor output has more lumens per watt of output
than blue LED light has, even after the Stokes loss, luminous efficacy of
a white LED should be improved by adding more phosphor. Yet, in most
cases the "warm white version" has less efficacy than the version with a
usual higher color temperature. Whatever problem is involved with
thicker layers of phosphor or more concentrated phosphor could be being
solved given recent efficacy highs being associated with color
temperatures lower than what I consider usual for white LEDs.

While better phosphors may have helped reduce the CCT, I
believe that even the early phosphors had a quantum
efficiency over 80%, which indicates that very limited
efficacy gain is available in this area.
Somehow I suspect some would call a phosphor loss due to absorption or
other blockage an "extraction" issue.

However, I have noticed the "wallplug efficiencies" of recent high
efficacy white LEDs (a couple of which I have) to exceed those of any blue
ones I ever had my hands on. Maybe the really good blue ones got better
but the really good blue chips are being used to make white LEDs?

Well, blue light doesn't produce very many lm/W, so this is
not surprising.
Another thing I noticed in the past year or two: Some trend of the peak
wavelength of the "blue peak" in the spectra of white LEDs getting a
little shorter in wavelength. I see two advantages to this and a possible
little downside:

1) Greater percentage of output can be from phosphor for same CCT and
efficacy can be increased, since 450 nm has greater "blue efficacy" than
470 nm

2) The color is a little less greenish, allowing a more phosphor-
dominated lower-CCT color (with more lumens per output watt) without
getting noticeably more greenish than "blackbody".

Downside: Lower scotopic/photopic ratio. In applications where scotopic
vision is significant, such as nightlights, camping lanterns, some outdoor
lighting and some usage of some flashlights, improvement in illumination
ability will be less than the improvement in photometric performance -
although I see improvement still advancing.
However, I do not consider this a big issue, especially since in most
room lighting scotopic vision has a significance at most to an extent
that is a subject of controversy.

As long as LEDs and other light sources are being sold on
the basis of photopic lumens, there are big incentives to
trade off scotopic lumens to get photopic lumens.

--
Vic Roberts
http://www.RobertsResearchInc.com
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site without written permission.
 
D

Don Klipstein

Jan 1, 1970
0
Victor Roberts said:
Well, blue light doesn't produce very many lm/W, so this is
not surprising.

I was talking about radiometric efficiency - I thought "wallplug
efficiency" of LEDs, which I always saw stated as a percentage figure, was
reasonably understood to be radiometric.

- Don Klipstein ([email protected])
 
V

Victor Roberts

Jan 1, 1970
0
I was talking about radiometric efficiency - I thought "wallplug
efficiency" of LEDs, which I always saw stated as a percentage figure, was
reasonably understood to be radiometric.

Sorry, I misunderstood. If you mean watts out divided by
watts in, then, yes, it is quite surprising.


--
Vic Roberts
http://www.RobertsResearchInc.com
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V

Victor Roberts

Jan 1, 1970
0
On 31 Jan 2007 11:17:52 -0800, "RHRRC"

[snip]
Wallplug efficiency using the radiometric ouput is more nonesense to
allow the already massively overblown claims of a significant number
of led luminaire manufacturers to be exaggerated even more.
Take any led, connect it to its current source with very fine wires,
let it hang free in air. 'RadiometricEfficiency' of the led is near
100%.
Dunno what the light ouput is - in fact lumen output does affect the
radiometric efficiency of this led in any way.

PS. watts out divided by watts in is always unity if you measure
everything


Don was not talking about measuring "everything." He was
discussing the radiated power of the "blue" light and the
radiated power of "white" light, each compared to the input
power. This does not tell us how "bright" the LED is as
perceived by our eye/brain system, but does tell us
something about the operating efficiency of the LED.

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
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This information is provided for educational purposes only.
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D

Don Klipstein

Jan 1, 1970
0
Sorry, I misunderstood. If you mean watts out divided by
watts in, then, yes, it is quite surprising.

It did already occur to me to add some followup:

This "wallplug efficiency" (radiometric efficiency of an LED lamp) that I
see in a few press releases by Cree and some news bits in ledsmagazine.com
is a figure that I now see many preferring to call "conversion efficency".
This figure is watts of visible light out per watt of power intothe LED.
I am now seeing how "wallplug efficiency" can be a choice of words that
can be questioned, since this figure does not assume or take into account
any ballast losses.

- Don Klipstein ([email protected])
 
D

Don Klipstein

Jan 1, 1970
0
Wallplug efficiency using the radiometric ouput is more nonesense to
allow the already massively overblown claims of a significant number
of led luminaire manufacturers to be exaggerated even more.
Take any led, connect it to its current source with very fine wires,
let it hang free in air. 'RadiometricEfficiency' of the led is near
100%.
Dunno what the light ouput is - in fact lumen output does affect the
radiometric efficiency of this led in any way.

PS. watts out divided by watts in is always unity if you measure
everything

I think that even in your described situation, most of the radiated
output is visible light, or "optical band radiation" of wavelengths
around/"close to" those that the LED is intended to radiate.
As for the "loss"? I think that gets convected and conducted more than
radiated, especially when the temperature of the lamp is in a good area -
and achieving that can require adding heat-conduction assistance means
such as a heatsink.

- Don Klipstein ([email protected])
 
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