Are you sure this is "LED"?
https://www.bing.com/images/search?view=detailV2&id=FDAEB896E301A2B1ACFFB2F246CB2EC0E1E0892A&thid=OIP.FYHkQP9XN3EmpkXJFXaohwHaFj&mediaurl=https%3A%2F%2Fwww.apogeeinstruments.com%2Fcontent%2Fquantum-sensors%2Fpar-explained%2Fred-LED-635nm.jpg&exph=450&expw=600&q=red+led+spectra&selectedindex=9&ajaxhist=0&vt=0&eim=1,2,6
I'm thinking of typical laser 635nm or 620nm typical laser LED. I agree they
are "narrow-band" but never like the one you showed from GE? I'd have to
measure them.... to be sure. I confess I never took the time to spectrally
measure red LEDs...
My (current) idea of "spikey" is a Mercury spectra (Hg) such as used in
commercial fluorescent tubes. You could say the 547nm "line", for instance,
it's "very narrow". Unlike a "typical" LED but your GE "Phosphor" LED is making
me think about what I consider "spikey"?
I'm not aware that "typical" LEDs have "spikey" spectra. White LEDs is anything
but narrow? Such as the type used in "popular" white LED backlit, like this one
:
https://www.bing.com/images/search?view=detailV2&id=4B165445A5361568DB8B56D4D5CD12EA7736C68E&thid=OIP.5KBz9X783ACY2KYQ9Pd1fwHaEU&mediaurl=https%3A%2F%2Finsearchofmornings.files.wordpress.com%2F2010%2F01%2Fwhite-led-spectrograph-1.gif&exph=442&expw=759&q=white+led+spectrum&selectedindex=56&ajaxhist=0&vt=0&eim=1,2,6
I understand two LEDs are used in combination in this kind of application, a
"wide-band" LED and a "narrow-band" blue LED which is "spikier" than the white
LED - no question.
But, coming back to Ben's comment, I am not convinced that the resultant
transparency ICC profile will be "difficult" or somehow "inferior" because of
"spikey LEDs"? That may not be the gist of his comment but that's what I was
reacting to. For sure, we can all agree that LEDs are no "spikier" than Mercury
lines. And yet, the whole world still view color images under this kind of
lighting (for now). I, personally, would not have difficulty measuring patches
on an LED backlight. But I may be wrong. This is something I've never tried, I
will confess. YET, for those who build transparency ICC profiles, today, a lot
of them are used in "fluorescent lighting" backlights, at theaters and shopping
centers.
Thanks for the GE link, Johan. I'm always willing to learn.
/ Roger
-----Original Message-----
From: argyllcms-bounce@xxxxxxxxxxxxx <argyllcms-bounce@xxxxxxxxxxxxx> On Behalf
Of johan@xxxxxx
Sent: Friday, October 4, 2019 6:17 PM
To: argyllcms@xxxxxxxxxxxxx
Subject: [argyllcms] Re: Backlit (transmission) profiling with i1
Roger,
LEDs typically consists of a blue LED and a phosphor. Since the yellow
light-emitting YAG:Ce phosphor lacks energy in the red, a second phosphor is
often added. For display applications, there could be even three kinds of
phosphors, RGB. GE has a popular red phosphor
(http://www.geradiantred.com/about/) but it's indeed very spiky, and so is the
blue LED peak.
-Johan
-----Original Message-----
From: argyllcms-bounce@xxxxxxxxxxxxx <argyllcms-bounce@xxxxxxxxxxxxx> On Behalf
Of graxx@xxxxxxxxxxxx
Sent: Saturday, October 5, 2019 3:22 AM
To: argyllcms@xxxxxxxxxxxxx
Subject: [argyllcms] Re: Backlit (transmission) profiling with i1
Ben,
I was asked recently whether I could create backlit profiles for transparency
media. As I don't have an instrument that can measure in transparency, I
thought I could use a non-contact colorimeter, I was thinking of mounting the
instrument on a tripod to always aim at the same angle, normal, relative to the
patches and all I would have to do was to move the target so that all patches
would be measured on the same "source of light". I don't see why that would not
work? But I was not sure about the light source itself? My thinking was to use
the same kind of fluorescent tubes used in these point of sale "backlights".
That way, by using the same type of lighting, I was guaranteed some success.
Now, why do you say that LED spectrum would be spiky? Fluorescent tubes
spectrum are, by nature, spiky. But LED? Seems to me they're rather smooth.
/ Roger
-----Original Message-----
From: argyllcms-bounce@xxxxxxxxxxxxx <argyllcms-bounce@xxxxxxxxxxxxx> On Behalf
Of Ben Goren
Sent: Friday, October 4, 2019 2:10 PM
To: argyllcms@xxxxxxxxxxxxx
Subject: [argyllcms] Re: Backlit (transmission) profiling with i1
On Oct 4, 2019, at 9:11 AM, Alexey Gribunin <Gribunin@xxxxxxx> wrote:
Now I'm using iPad (!) and found it much more stable (auto-brightness=off).