I was wrong, they *do* offer an ISO-3664:2009 compliant solution:
https://store.yujiintl.com/collections/standard-illuminant/products/standard-illuminant-cri-98-d50-5000k-t8-led-tube-pro-iso3664-2009
But it's in the form of a T8 tube (they don't have it in "LED strip".
I think I'd be interested in ordering a small tube, to experiment with.
Thanks Ilah!
/ Roger
-----Original Message-----
From: argyllcms-bounce@xxxxxxxxxxxxx <argyllcms-bounce@xxxxxxxxxxxxx> On Behalf
Of graxx@xxxxxxxxxxxx
Sent: Wednesday, October 30, 2019 2:42 PM
To: argyllcms@xxxxxxxxxxxxx
Subject: [argyllcms] Re: Backlit (transmission) profiling with i1
Ilah,
These "Yuji VTC D50 LED" are promising.
Not cheap, though ☹
They are smart to state "ISO-3664:2000", which means they have not figured out
how to be "ISO-3664:2009" compliant yet?
Best / Roger
-----Original Message-----
From: argyllcms-bounce@xxxxxxxxxxxxx <argyllcms-bounce@xxxxxxxxxxxxx> On Behalf
Of Iliah Borg
Sent: Wednesday, October 30, 2019 2:32 PM
To: argyllcms@xxxxxxxxxxxxx
Subject: [argyllcms] Re: Backlit (transmission) profiling with i1
In my experience even Yuji COBs (we use those for our projects) can't be used
without a spectrometer.
Check the spectra here:
https://store.yujiintl.com/collections/standard-illuminant
For a camera, one needs at least 400 .. 700 nm range
On Oct 30, 2019, at 2:15 PM, Kamil Tresnak wrote:
Czech friend from Prague 😂
*my led strips" was no good, profiles have problems in some parts of
spectra i1pro, fake transparent (as described in argyll manual, spot
mode (we discussed this some time ago), so time consuming, but strip
reading never worked for me)
Here is an example - just a mobile photo of a quick view against an undefined
ceiling light ...
https://drive.google.com/file/d/1dDLBLD1cVR6kjtwcsYJik7PdfZotZtSN/view
?usp=sharing
K.
On Wed, Oct 30, 2019 at 7:05 PM <graxx@xxxxxxxxxxxx> wrote:
Hello Kamil – russian friend! (Dobroi ultra, Kagh dielo?)
So “LED stripes” light was not good?
How were you taking measurements?
I1pro? In “Ambient” mode?
/ Roger
From: argyllcms-bounce@xxxxxxxxxxxxx <argyllcms-bounce@xxxxxxxxxxxxx>
On Behalf Of Kamil Tresnak
Sent: Wednesday, October 30, 2019 2:01 PM
To: argyllcms@xxxxxxxxxxxxx
Subject: [argyllcms] Re: Backlit (transmission) profiling with i1
Hello Roger,
not talked a while, friend :)
Roger, go for incandescent, exactly as Ben recommended (even with fan 🙂 ),
and you will be a hero.
This is my real-world experience. I tried a few sources, even LED stripes,
and with bad results.
Of course, i don't know every LED source in the world, but i don't want waste
my time searching for a suitable one.
Best!
Kamil
On Fri, Oct 4, 2019 at 8:22 PM <graxx@xxxxxxxxxxxx> wrote:
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).
Curious that at an LED display should work well as a backlight for
transmissive profiling. The spectrum is going to be spiky as all get-out, no?
Light boxes are readily available, and an almost trivial DIY project. The
biggest challenge these days would be finding incandescent bulbs. You’ll want
to provide lots of ventilation in the illumination chamber, possibly even
including an exhaust fan if you’re pumping enough wattage into the box. But
the design...just get a pair of same-sized translucent plastic sheets. Using
your favorite construction method (could be anywhere from foamcore held
together with duct tape to fine woodworking dovetail joinery), build a box
that holds the one sheet at the top, the other in the middle, and the bulb(s)
at the bottom. If the construction material isn’t already white, paint the
inside white (cheap interior house paint is fine). If the box isn’t bright
enough, you need either more transparent sheets (start with the middle
diffuser) or more wattage (be careful of heat!). If you have visible bright
spots, you need a middle diffuser that’s more opaque.
That’s all there is to it.
I would again very, very highly recommend unfiltered incandescent lights for
profiling purposes. The spectrum is beautifully smooth as a fundamental
property of the physics. That it’s not necessarily the ideal color
temperature, etc., is entirely irrelevant; the math to fix that is trivial.
Spectral spikiness...can cause all kinds of problems.
I would even recommend “hot” incandescents for color critical
photography over the best flashes. Not that the best flashes are
problematic; they’re just not as spectrally smooth as incandescents.
(Of course, non-color considerations could quickly tip the scales to
flashes. I wouldn’t try to photograph humans in a studio setting with
hot lights, for example.)
Cheers,
b&
