LED lights for filmmaking

[Bob Masta]

Most people have three types. Some women have four - which is probably why
you get arguments about whether that dress/tie/whatever is blue or green.

Not to mention all the dichromats (color-blind) viewers of the world.

There is an additional phenomenon recently described/proposed
by my old friend Angela Brown. Seems the blue cones are easily
damaged by UV exposure, which gives old vision a brownish tint
(called "brunescence"). She and her co-author noted that in
equatorial countries (lots of UV exposure) there tends to be be
little or no distinction between shades of blue... most of the
languages in those countries tend to call all bluish colors by
the same general name, which translates to something like
"dark" in each language. Tests on subjects show that they
do indeed have significant brunescence by early adulthood,
comparable to 90-year-old outdoor workers in northern
regions. She has a demo of what the differences look
like with and without this brunescence, and it's pretty
dramatic. Unfortunately, it's not available on the Web
anywhere... you have to attend one of her talks
to see it, at the moment.

Best regards,



Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com

 

[Don Klipstein]

Don - can you please post the manufacturer and part number of such an
LED?

Nichia NCCW022, of brightness rank Jc - the rank that includes the 42
lumen output mentioned in:

http://www.nichia.co.jp/product/led-smd-powerled.html

That web page mentions 42 lumens as some sort of typical, and the
minimum for brightness rank Jc is 36.

This is at case temperature of 25 C, as opposed to Lumileds specifying a
junction temperature of 25 C, according to Nichia's datasheet.

Voltage drop is typically 3.6 volts, max. for the upper-middle voltage
rank drop is 4.0 volts, and max for the highest rank (worst) voltage drop
is 4.3 volts.

36 lumens at 4.3 volts at .35 amp works out to... 23.9 lumens/watt

This is a real worst case assuming you get the brightness rank that
includes the lumen figure mentioned in the above-mentioned web page.

"Typical" (maybe a bit optimistic for now) is 42 lumens at 3.6 volts at
..35 amp, which works out to 33 lumens/watt.

I would be a bit concerned about these figures being a bit optimistic
because most of the major manufacturers appear to have been one-upping
each other in their claims recently now that Cree is in the 350 mA white
LED game.

However, Cree has been advancing somewhat steadily at least their
claimed blue LED chip performance over the years, so I expect white
LED output to advance enough for the current claims to soon enough be
conservative rather than optimistic. Optimistic would then be the next
round of even higher claims for output and overall luminous efficacy.

(Cree has a 350 mA white LED with output minimum 40 typical 45 lumens
supposedly hitting production next month. I believe, based on the
datasheet for the "dice" (chips) that I believe they use, that the
voltage drop is typically 3.4, maximum 3.9 volts. This works out
to luminous efficacy of minimum 29.3 "typically" 37.5 lumens/watt. This
is one of their "XL7090" LED "lamps".
Cree specifies ambient temperature of 25 degrees C for their current
XL7090 products in http://www.cree.com/Products/lmp_7090.asp
-?? specify ambient temperature rather than case temperature for a product
that requires a heatsink??)

When I look at the data for the most efficient white LED that can be
purchased, which are the Lumileds Luxeon III LEDs operating at 700 ma,
and then adjust for minimum guaranteed output instead of "typical"
output and adjust for maximum guaranteed operating voltage instead of
"typical" operating voltage and finally calculate the junction
temperature for a heat sink temperature of 25C and adjust for the
decrease in output as a function of junction temperature I get an
efficacy of slightly less than 16 lm/W, which is about the same
efficacy as a normal 100-watt, 750-hour incandescent lamp.

Close to what I got for Luxeon III "star"... I figure about 16.1
lumens/watt if the worst case voltage drop decreases with increasing
temperature the same as typical voltage drop does. With a thermal
resistance of 17 degrees C per watt and 3.06 watts, junction temp. is 77
degrees C. Looks like you get 82% of the light output that you get with
the junction temperature at 25 degrees C.
The Luxeon III "emitter" has a thermal resistance of 13 degrees C per
watt as opposed to 17 for the "star", making the worst case junction
temperature slightly over 12 degrees C cooler, increasing light output
slightly over 4% (and voltage drop .5-.6%) higher - let's say worst case
overall luminous efficacy is 3.5% better than that of the "star", or 16.6
lumens/watt. Of course this assumes cooling the smaller heatsink surface
of the "emitter" to 25 degrees C.

I do not like the way Lumileds has their nominal performance specified
at a junction temperature that requires a heatsink temperature of
typically -19 degrees C (-2 degrees F) (for Luxeon III "star") if operated
continuously.

- Don Klipstein ([email protected])

 

[Bob Masta]

There is an additional phenomenon recently described/proposed
by my old friend Angela Brown. Seems the blue cones are easily
damaged by UV exposure, which gives old vision a brownish tint
(called "brunescence").

CORRECTION: Brunescence is not due to damage to the
blue cones, but rather to damage to the lens. (I'd guess
that might even protect the blue cones, by restricting the
light reaching them.)

"Senescence" is due to damage to little grey cells that
make me forget these critical details!

She and her co-author noted that in
equatorial countries (lots of UV exposure) there tends to be be
little or no distinction between shades of blue... most of the
languages in those countries tend to call all bluish colors by
the same general name, which translates to something like
"dark" in each language. Tests on subjects show that they
do indeed have significant brunescence by early adulthood,
comparable to 90-year-old outdoor workers in northern
regions. She has a demo of what the differences look
like with and without this brunescence, and it's pretty
dramatic. Unfortunately, it's not available on the Web
anywhere... you have to attend one of her talks
to see it, at the moment.

Sorry for any confusion my senescence may have
caused!


Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com

 

[Victor Roberts]

Nichia NCCW022, of brightness rank Jc - the rank that includes the 42
lumen output mentioned in:

http://www.nichia.co.jp/product/led-smd-powerled.html

That web page mentions 42 lumens as some sort of typical, and the
minimum for brightness rank Jc is 36.

Good find, but this is not a the real minimum that a customer would
find in an order of these devices. Nichia states on their data sheet
for this LED: "One delivery will include up to two color ranks, four
luminous flux ranks and three forward voltage ranks of the product.
THE QUANTITY-RATIO OF THE RANKS IS DECIDED BY NICHIA." [Emphasis is
mine.]

So, the customer has no control at all over what rank LEDs he or she
gets from Nichia and cannot design a product or application around the
so-called minimum output of the Rank Jc device. They must assume that
some, or perhaps all, of the devices they receive will be Rank Ja,
which has only one half the performance of the Rank Jc devices.

This is at case temperature of 25 C, as opposed to Lumileds specifying a
junction temperature of 25 C, according to Nichia's datasheet.

Voltage drop is typically 3.6 volts, max. for the upper-middle voltage
rank drop is 4.0 volts, and max for the highest rank (worst) voltage drop
is 4.3 volts.

36 lumens at 4.3 volts at .35 amp works out to... 23.9 lumens/watt

This is a real worst case assuming you get the brightness rank that
includes the lumen figure mentioned in the above-mentioned web page.

No, the real worst case is about half your number, based on the
assumption that any order would include some or all Rank Ja devices.

"Typical" (maybe a bit optimistic for now) is 42 lumens at 3.6 volts at
.35 amp, which works out to 33 lumens/watt.

I would be a bit concerned about these figures being a bit optimistic
because most of the major manufacturers appear to have been one-upping
each other in their claims recently now that Cree is in the 350 mA white
LED game.

However, Cree has been advancing somewhat steadily at least their
claimed blue LED chip performance over the years, so I expect white
LED output to advance enough for the current claims to soon enough be
conservative rather than optimistic. Optimistic would then be the next
round of even higher claims for output and overall luminous efficacy.

(Cree has a 350 mA white LED with output minimum 40 typical 45 lumens
supposedly hitting production next month. I believe, based on the
datasheet for the "dice" (chips) that I believe they use, that the
voltage drop is typically 3.4, maximum 3.9 volts. This works out
to luminous efficacy of minimum 29.3 "typically" 37.5 lumens/watt. This
is one of their "XL7090" LED "lamps".
Cree specifies ambient temperature of 25 degrees C for their current
XL7090 products in http://www.cree.com/Products/lmp_7090.asp
-?? specify ambient temperature rather than case temperature for a product
that requires a heatsink??)

I find only typical output data given at the link you provide. I agree
that the specifying ambient temperature is a bit confusing for a
device that needs an additional heat sink.

Close to what I got for Luxeon III "star"... I figure about 16.1
lumens/watt if the worst case voltage drop decreases with increasing
temperature the same as typical voltage drop does. With a thermal
resistance of 17 degrees C per watt and 3.06 watts, junction temp. is 77
degrees C. Looks like you get 82% of the light output that you get with
the junction temperature at 25 degrees C.
The Luxeon III "emitter" has a thermal resistance of 13 degrees C per
watt as opposed to 17 for the "star", making the worst case junction
temperature slightly over 12 degrees C cooler, increasing light output
slightly over 4% (and voltage drop .5-.6%) higher - let's say worst case
overall luminous efficacy is 3.5% better than that of the "star", or 16.6
lumens/watt. Of course this assumes cooling the smaller heatsink surface
of the "emitter" to 25 degrees C.

I do not like the way Lumileds has their nominal performance specified
at a junction temperature that requires a heatsink temperature of
typically -19 degrees C (-2 degrees F) (for Luxeon III "star") if operated
continuously.

- Don Klipstein ([email protected])

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
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[Don Klipstein]

I find only typical output data given at the link you provide. I agree
that the specifying ambient temperature is a bit confusing for a
device that needs an additional heat sink.

Sorry, the 40 lumen minimum for the soon-to-come part is in this Cree
press release:

http://www.cree.com/News/news210.asp

- Don Klipstein ([email protected])

 

[Victor Roberts]

Sorry, the 40 lumen minimum for the soon-to-come part is in this Cree
press release:

http://www.cree.com/News/news210.asp

- Don Klipstein ([email protected])

Thanks Don.

--
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.