Today we’re gonna get pretty nerdy. I’ve got a little demo
set up here so that we can discuss the different metrics
for measuring the colour quality of lights,
the flaws of those evaluations, and hopefully make you a more
informed buyer when it comes time to purchase lights,
and give you a better understanding
of how to match them. Let’s get Undone!
[offbeat music]
♪ Gerald Undone ♪
♪ He's crazy ♪
What’s happening, everybody?! I’m Gerald Undone
and I’m just pink.
Alright, disclosure time.
This video is a partnership between me and Sekonic.
They wanted a video discussing the different tools their C800
spectrometer offers, and I wanted a sponsor
for this nerdy, light-quality deep dive.
They provided the C800 to me for free and threw some
cash my way to make this video.
The other thing you should know is that I am not a colour
scientist or a physicist, so the information I’m going to
be providing is through the filter of an inspired
enthusiast, but I did consult some of those experts
when it came to scripting and researching this video.
Over here I’ve got an Aputure F7 pointed at
the Sekonic C800, so that I can actively illustrate
some of the topics we’ll cover, but this is not a proper
test or review of this panel as I have other
lights interfering with the results,
so this is purely for demonstration purposes.
Now, if you’ve ever been shopping for or comparing
lights you’ve probably seen ratings like a CRI of 95+
or a TLCI of 97 to try and sell you on the idea that
the light is very good at reproducing colours accurately.
But there’s actually a few other metrics for this
like TLMF, TM-30, and SSI, with the latter two being much
more useful for the average shooter than CRI or TLCI.
So, let’s start with CRI and its shortcomings.
CRI, which stands for Color Rendering Index,
was originally designed for judging fluorescent lamps
and is based on 15 colours.
However, most of the time when manufacturers put CRI
ratings on their products, it’s actually only an average
of the first eight of those colours and it’s evaluated
against how well the human eye would be able to accurately
perceive those colours under ideal daylight conditions.
There is CRI extended, which does average all 15 colours,
but that’s not what’s usually advertised by manufacturers.
The big problem with CRI, however, is that light makers
can tune their lights to beat this system
by just rendering those specific eight colours well.
It is still useful for letting you know
if a light is absolutely terrible.
For example, if a light scores a CRI of 70,
you know that it’s abysmal for colour quality,
but scoring 95 doesn’t necessarily mean that the light
is good, because they could have just gamed the system.
Strangely, despite these shortcomings,
CRI is still the standard, and that’s mainly
because standards are very hard to change.
But slowly, users are becoming more educated
and asking for other metrics
and some keen manufacturers are starting to provide those.
Let’s do a little measurement here using the Sekonic.
Alright, so, we’re just gonna tap on CRI,
and then we will will measure this light.
And we have a result of 96.5.
Now, again, this isn’t me saying that the Aputure F7
is a 96.5 ‘cause there’s other lights going on in here and--
but for this test case, you know, we’re getting a CRI
of 96.5. So, this will show the different colours here,
and you can see all 15 colours and how accurate
each one of them is against their ideal.
Now, some people like to go in here and tell you
just the specific one, like, “Oh, my R8 is really good,
or the R15 is really good,” whatever.
But when you see it on a box, and it says CRI of 95+,
it’s an average, usually of the first eight colours.
Now, another common,
but dated and somewhat flawed metric is TLCI.
It, too, is based on evaluating specific colour chips.
In this case, it’s actually the 18 colours
found on the X-Rite ColorChecker Classic.
The big difference between CRI and TLCI,
though, is the observer.
CRI, as we said, is based on how the human eye sees colour,
but TLCI is based on how older,
three-chip broadcast cameras see colour, hence the name,
Television Lighting Consistency Index. But this can actually
pose problems for people who use modern camera sensors,
which is likely most of the audience watching this video.
So, in terms of TLCI’s overall utility,
it’s like CRI in the sense that a low score might tell you
that a light is bad, but a high score doesn’t guarantee
that a light will be good with your modern camera.
So, we’ll choose TLCI, and then we will do a reading.
So, it’s showing a colour temperature of 5244,
and our TLCI of 99.
By the way, I have the light set to 5500K.
So, that TLCI is really, really high.
The highest you can go is 100.
Now, there’s also a companion metric that you can see here
called TLMF or Television Luminaire Matching Factor,
which also incorporates those grey chips on the bottom
of the ColorChecker to give
a comparative score between lights to help
with light matching on TV sets. But the adoption rate of this
metric is low and it’s limited in the same way that
TLCI is, because it’s a component of TLCI.
So, for this one we’re gonna need to save a light,
so that we can compare it to another one.
So, since we already took a reading of this combination,
if we press the memory button on the side--
this one’s saved as “Untitled - 01."
So, now we can actually load that into the slot
below, "Untitled - 01," and press okay.
And so we have that light below there.
And now, if we were to do a reading,
it’s gonna come up with 100, because nothing changed.
So, you can see the TLMF is 100,
meaning that this combination perfectly matches
the combination that we loaded into the bottom.
Let’s say we change it a little bit by turning off this light
and then doing another reading. It should be slightly different.
So, now we’re only getting a TLMF of 60, meaning this
current combination is only sort of a 60 percent match,
if you will, to the combination before.
Now, when it comes to metrics based on human vision,
the best one and the one
that manufacturers should be using is the TM-30.
Instead of the limited amount of colours used in a CRI score,
TM-30 uses 99 more practically chosen colours
and involves saturation.
With CRI, you could have two lights that score the same CRI,
but that produce wildly different saturations.
With TM-30, you’re given an Rf score,
which is the fidelity score, similar in a sense to CRI,
with 100 being perfect, but also an Rg score
which ranges from 60-140, with 60 being undersaturated,
and 140 being oversaturated, and 100 being spot on.
And given that it uses 99 colours, it’s much harder
for the manufacturers to game their lights to beat the test.
In my opinion, this should completely
replace CRI as the standard.
The only flaw I see with it is
that it's still based on human vision. Let’s do another test.
Alright, so we’ll pick TM-30 over here.
Now, sometimes you might see TM-30-15,
or TM-30-18. I believe that’s just the year.
The last two digits are the year that it was--
the most recent version.
So, I think right now we’re on TM-30-18.
‘Cause I think the latest one is from 2018, but TM-30
is the parent thing and that’s all that really matters.
Alright, so based on our reading,
we can see that we’re getting an Rf of 93.
That means that our colour fidelity,
how accurate we are, is about 93 out of 100,
with all 99 colours being measured.
And then over here, we’ve got an Rg of 101.
Which is very good for saturation,
because 100 would be sort of the ideal saturation, 60 would
mean you’re undersaturated, 140 would be oversaturated,
as you work towards those extremes.
But 101 is a very good saturation.
And another thing that’s cool about TM-30 is,
you see this little vector graph at the bottom here?
It shows you, especially with the little arrows,
what colours are more saturated or less saturated.
So, you see down here, the further away that it pulls
from this, sort of, black circle--so if it goes on
the outside, that colour's being more saturated,
and if it goes on the inside,
that colour’s less saturated, so you could use that
to try and evaluate, you know, where your weaknesses are.
So, overall, this is a very useful metric at not only,
you know, seeing how accurate colours are,
but where your flaws are, which one’s more saturated, etc.
And it’s much harder to game than CRI, so vastly superior.
Finally, we have SSI, which stands
for Spectral Similarity Index and is probably the most
logical metric for video shooters and filmmakers.
It’s based on daylight and tungsten,
the most common lights used on set.
And the score is based on how closely
the spectral fingerprint of a measured light lines up
when compared to a known light source
like natural daylight or a perfect tungsten source.
Fun fact about that!
Did you know that the colour temperature of 3200K
or “tungsten” is based on heating a tungsten filament up
to 3200 degrees Kelvin and that the colour and light
quality of that extremely hot filament is
what we base our understanding of 3200K white balance on.
And this is what makes SSI special:
it removes the observer from the equation
and instead scores lights based on
their similarity to these known, ideal light sources.
It either matches well or it doesn’t,
no human vision required.
So, to test SSI against one of those known sources,
you choose SSI, then you have to choose one
of the memory slots, and choose standard light source
and then we can choose what we want.
So, we’ve got our CIE standards in here,
we’ve got tungsten like we’ve mentioned.
So, we can choose that.
And we'll also choose CIE D55 for our daylight source,
because this light is set to 5500K.
So, now we can automatically see that
for an SSI for tungsten, we’re only scoring a 55,
which makes sense because the light is not set to tungsten.
But for the daylight at 5500K, which is the one down here,
D55, we’re getting a 74.
But if we adjust the colour temperature of this light down
to 3200K to give us that tungsten measurement, and then
we read it again, we should see the SSI for tungsten go up.
And it did; it’s up to 73 now.
So, again, this isn’t perfect because I have other lights
that are sort of spoiling this, but that’s the idea.
It’s based on how closely now is this 3200K matching tungsten.
I believe the F7 would score better if the test was ideal.
Let’s put it back to 5500K.
But what makes the Sekonic C-800 great
is that you can also use SSI to see how well
the spectrum of one light matches to another.
So, perhaps you only had one Arri SkyPanel,
but you needed two lights.
You could take a reading of the SSI of that SkyPanel,
save it in the C-800’s memory, and then go testing other
lights to get the closest match possible,
with a score of 100 being a perfect match.
But when comparing your light to one of the pre-programmed
ideal sources, you’re likely not going to score 100,
so you want to get at least 80.
90+ is excellent, 70-80 is fine, but you might
have a couple shifts, and less than 70 is no bueno.
And by the way, if you look at the graph down here,
you can see them overlaid, so the solid colours are
the actual measurement, and then the yellow hollow bars
are the perfect tungsten source.
Now, if we were to change this one to memory recall,
this could be--we’ll keep using the "Untitled - 01,"
which was the previous reading of this light.
But let’s say that that was a saved--
the Arri SkyPanel, that’s what that was.
So, we press okay.
So, in this case your yellow bars would be your previously
measured light, and then you would do a reading on
your new setup, and then you would see
how closely they line up.
And in this case, we scored 100,
which makes sense, because it’s the exact same configuration.
And so, now you can see that the full bars are completely
filling the hollow bars, and your spectrums are lining up,
is the idea, because nothing changed.
But this can help you see how close, and again, if you get
90+ when comparing lights,
you’re probably pretty good to go.
Now, while playing around with this C-800 to make this video,
I found a couple other tools that I think are pretty cool.
First off, it has a tool that lets
you put in a target temperature and then tells you
what gels you need on your lights to achieve that.
So, we choose "Filter," and then up here we have a target
of 5600K. You can tap on that to set it to whatever you want.
We’re measuring 5248K, and so this suggests that
if we were to use this gel here, which is a 1/8 CTB,
because we need to cool off our light a little bit, that we
would get to the ideal colour temperature that we wanted.
And then the one right below shows your tint,
your green-magenta shifts.
So, right now it’s showing 0.1 green,
meaning that we’re a little bit on the magenta side,
and we need a 0.1 green to rectify that.
And then right below it, it would show a gel if there
was an applicable one, but I think because
it’s so marginal, there’s not really a gel
for the 0.1 green there, so just go with it.
And if you use full colour panels that work
with X&Y coordinates, like a SkyPanel, for example,
you could take an X&Y reading and then input
those coordinates into your second light
like the Aputure P300c for precision matching.
Which is pretty cool.
But even if you’re just using a little HSI panel like
the Aputure MC, you can have the C-800 display the hue
and saturation of a source, so that you can input that into
your little RGB light, which has actually been pretty
handy for me when it came to matching different RGB colours.
So, I’ve got this set to a hue of 15 degrees,
and a saturation of 100.
Now, it’s probably going to be a little bit off again
because of all the lights, but let’s do a reading
over here, and see what it comes up with.
So, we go to text, and this is where you can
customize it to show whatever you want, like I said.
The X and Y coordinates or whatever.
But I’ve got it to show hue and saturation for this test,
and you can just tap on it to change those.
Instead, we’re gonna do a little reading like this,
and we’ve got 14 degrees and 100%.
So, that’s very, very close to what I have set.
So then you can take your other panel that maybe
wasn’t made by the same manufacturer,
and put in those--the hue and saturation to get a match.
Obviously if they’re the same light,
you can just put the same hue and saturation.
But sometimes, one company’s RGB light
isn’t the same hue as another company’s RGB light,
and so this can help you balance those out.
Which is awesome. Alright, that’s pretty much it.
I hope that this video will make you more informed
light buyers in the future.
Ideally, I think manufacturers should move
from using CRI and TLCI to using TM-30 and SSI,
as TM-30 is a better metric
for evaluating lights on their own,
and SSI is much more useful for matching lights
or comparing lights to known sources.
But hey, I don’t make the rules.
But that's gonna be it for me. I hope you found this video
entertaining or at least helpful. And if you did,
make sure you leave it the old thumbs up
and consider subscribing if you haven't already.
But if you did not find this video helpful or entertaining,
try setting the playback speed to 75%.
Alright... I'm done.