If you've ever been shopping for a LED light panel,
a monitor or even a lightbulb and found yourself
confused or annoyed at the various units there are
for measuring the intensity of those products
like nits, lux and lumens? Then, I've got a video for you.
Let's get Undone.
[offbeat music] ♪ Gerald Undone ♪
♪ He's crazy ♪
Whazzzap? I'm Gerald Undone
and today we're talking about units for measuring light.
Now, I'm gonna try and avoid some of the more complicated
physics that would typically accompany this topic
because my goal is for you to be able to memorize
some of the basics of this guide and then use that
when making purchase decisions.
And I don't think that's really gonna work
if I bog this video down with too much math.
So, if there's any pedantic physicists watching,
consider yourself disclaimed. Alright, so let's start off
with the units that we're going to be focusing on.
First, we've got the lightbulb,
which is typically advertised using watts or lumens.
Then we've got light panels which deal with lux
and then we've got display screens like your phone,
computer monitor or Atomos recorder which use nits.
So, let's start off with watts
because they don't really belong.
The Watt is a unit of power, or more practically,
a unit of how much electricity
you're consuming over a period of time.
It's also a unit of radiant flux,
which is also how much radiometric power
is being emitted by a source,
which also relates to lightbulbs.
But since radiant flux doesn't indicate the power
of just the visible light, it's not that useful to us
for this video. So, instead think of watts
as how much that light is gonna cost you to run
or how big of a battery you'll need to power it.
Now, if all the lightbulbs were using the same filament
or technology, then the Watt might actually give you
a decent indication of how bright they'd seem
since more power should mean more output.
And, in that case, I suppose the Watt
would be doubly useful, but not so much today.
Because a 14-watt incandescent bulb
is not going to give you similar light emittance
to a 14-watt LED. But it's still useful
in knowing both of those bulbs would require 14W
when it comes to paying the electricity bill.
So, the better way to measure lightbulbs is with lumens
because it's consistently practical, even when you change
the technology inside the bulb or its power requirements.
Unlike radiant flux, the Lumen is a unit of luminous flux.
And when we say flux by the way,
just think of something flowing. It's a way of describing
the perception that an effect appears to be moving
across or through a surface.
And so, a lumen is the quantity of visible light
emitted by a source-- and the word "visible"
is important here, because this unit is weighted
toward the human eye's capabilities.
Now, when we talk about lumens, we're really talking
about Candela, which are the base units used
to measure luminous intensity and are roughly equal
to the light emitted from one wax candle.
And just like with lightbulbs and watts,
candles also have radiant intensity,
but we discount the wavelengths that aren't important
to the human eye and what we're left with
is luminous intensity. Because this intensity
has to be measured perceptually, visibly by the human eye,
we measure it at a solid angle and in a specific direction.
But lumens aren't limited to that
specific direction and angle,
and instead cover the entire sphere of radiation.
So, if a light is able to emit
1 cd in all directions uniformly,
it has a total luminous flux of 12.57 lm.
And so, if you take this LED bulb here,
which has a rating of 1500 lm,
that's like saying it has a similar intensity
to 120 wax candles emitting their light uniformly
in all directions. 1500 divided by 12.57
is about 120 candles rounded.
Now, hopefully you're still with me
because it's gonna get a whole lot easier from here out
now that we've established our basic units.
So, that's all great for lightbulbs, but what if you buy
a LED panel? They usually have a rating
of a certain amount of lux at a specified distance.
For instance, this LED panel has a rating
of 1500 lx at one meter. As I was saying,
it gets a lot easier now because as a Lumen
is a measurement of luminous flux,
a lux is a measure of luminous flux in an area.
So, you remember how I said that lumens are like candles
emitting their light uniformly in all directions?
Well, I didn't say how far because lumens
don't really care about distance, but lux do.
Think of lumens of how much light is being emitted
regardless of where you are: luminous flux.
But then think of lux as how much
of that light is hitting your face:
Illuminance; how illuminated you are.
So, a lux is equal to one Lumen per square meter.
Essentially, how well illuminated
that specific distance is.
And we use lux for light panels for two reasons.
One, we're likely lighting a subject,
so we need to understand how distance
is going to impact our lighting.
And two, because LED panels have beam angles
and if you're trying to describe how many lumens
are in a specific area, the beam angle is important.
If the beam angle is wider, even if the lumens are the same,
the amount of light radiating from your source,
the light will be less intense on your subject,
therefore your subject will have less illuminance
or be less illuminated.
A light with a more narrow beam angle
will have a higher lux at the same distance
because the lumens will be more focused
and thus, will illuminate your subject better.
Now, if you're trying to light your subjects with a lightbulbs,
they don't have a set beam angle
because they radiate in all directions,
which is why we measure them in lumens.
But there is a formula you can use for converting
the lumens of a lightbulb into lux
to give you a better sense of how it will compare
to a LED panel when it comes to illuminating your subject.
But as I said, I will avoid the math in this video,
so I'll put a link to a calculator you can use
to convert the lumens to lux in the description instead.
You can also use it the other way, to calculate
the lumens of your panels based on their lux
and their beam angles provided by the manufacturer.
So, if we put this lightbulb into the calculator
with an angle of 180 degrees because that's as wide
as it can possible be when you're viewing it
from one side, even though it's 360 degrees total
and then we put in 1 m, again we're gonna do it 1 m,
and this lightbulb is 1500 lm and hit calculate lux.
It tells us that this lightbulb
will give us 240 lx when 1 m away.
And this type of information can be useful
when comparing LED panels to lightbulb kits.
Now, there's another unit that covers a similar idea to this,
but it isn't SI standard, and it's called the foot-candle.
It also attempts to provide distance to the candela
and quantify illuminance, but at a rate of one candle
one foot away, hence foot-candle.
Now, I find this unit to be wonky
and luckily, you probably won't encounter it
on any lighting products related to photo and video,
but the conversion would be 10.764 lx
for every foot-candle, in case you encounter it.
Now, LED panels also have ratings in watts,
but again, this is more useful for power consumption
and battery pairings than it is for illuminance
as that power is subject to the efficiency
of the panel's circuitry and not the perceived output of light.
Okay, so we've talked about luminous flux,
which is the perceived power of a light, and illuminance,
which is the light incident on a surface.
Now, we need to talk about luminance,
which is the amount of light emitted
or reflected from an area, and this is where
your phone screens and monitors come in.
This is also where the term "brightness"
is more applicable and thus, why the control
to increase the output of your screens is called brightness.
Remember how we said that brightness is the quality
of how light will be received by your eye?
Well, luminance is how much luminous flux
will be detected by an eye from a particular angle of view,
or simply how bright a surface will appear.
And you know the angle of view is important
because if you've ever looked at a monitor
from off to the side, you'll know it's not nearly as intense
as when you look at it straight on.
And this brightness is measured in candela per squared meter,
but its also known as nits.
Essentially, if you were to look at a screen
and detect 250 candles of luminous power
at a specific angle, you would say
that it's emitting 250 nits. And 250 nits, by the way,
happens to be about the peak luminance
of a typical LCD panel, but HDR displays and phones
can go well beyond that.
The Atomos Ninja V, for example, is capable of 1000 nits.
Now, luminance isn't restricted to just screens,
but rather anything that is illuminated
can also have a luminance value.
So, for example, if I take this LED panel
and shine it at my desk, it will illuminate
a portion of my desk and will measure
that illumination in lux. But when I examine
that illuminated section on my desk,
the brightness of its reflection is its luminance
and we measure that in nits or candela per square meter.
And this can keep going back and forth
because that reflection might then illuminate my face
and that illumination would be measured in lux,
but then my face will be brighter
and that brightness as perceived by you
would be my luminance and would be measured in nits.
And this is true for things that don't have screens as well.
For example, if you were to look up
at a cloudy, overcast sky at midday,
the brightness of that sky might measure 2000 nits.
That's just how bright that sky looks to your eye.
But if you were to use that same overcast sky
to illuminate a subject that you want to photograph,
it might have an equivalent illuminating power
of 1000-2000 lx on your subject, depending on the clouds.
Fun fact, if however, you were to look at the sun
through a clear sky at midday,
you'd be staring at about 1.6 billion nits
and that's well beyond what your eyes can withstand.
Now, there is another unit used in photographic lighting
and that's the guide number found on strobes
and speed lights, but it is quite a bit different
than the types of units we've been discussing today,
so I think I'll make a separate video about that
and conclude this one here.
A lux is a measure of that luminous flux in an area.
Lux, flux, luminous flux-- it sounds funny.
...intensity of those products like Nix, Luts and lum--
Wha-ha-zap?
...and the various units there are for measuring
the intensity of those products like licks, nuts and--
Licks and nuts. Okay.
Wha-ha-zap?
So, if there's any pedantic physicists-ss.
[laughs] Physicists-ss. I sound like a [bleep] bumble bee.
As always, I hope you found this video helpful
or at least entertaining, and if you did,
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Alright... I'm done.