- [Instructor] A photometric light
can assume many different forms
to match the shapes of various lighting fixtures.
It can emit light from a point, which is the default,
but more accurately, we can emit light from an area
or a volume, using various shape primitives.
Let's render this in ActiveShade
with the default point light we've got in this scene.
Click to Render ActiveShade,
and let's bring this light down and we'll select it.
Grab the Move tool
and bring it down to about 0.2 meters above the floor.
Let me just type that in in the z-axis
down here if we want, 0.2 meters.
And with that light selected,
let's go over to the Modify panel,
and in the shape slash area shadows rollout,
we see that the Emit Light From Shape pulldown
is set to the default of Point
and that's that's a infinitesimally small point.
It has no area or volume.
In the General Parameters rollout,
the distribution type is defaulted to Uniform Spherical.
These default settings give us a point
that emits light in all directions equally.
Let's bring the intensity down
so we can better see the effect
of changing the light's shape.
We'll set the intensity to 500 lumens and press Enter.
So there's our point light source.
Back in that Shape Area Shadows rollout,
let's change the shape over to a different primitive.
We'll choose Line.
And now we've got a linear shape.
We can see it here.
Let's get it closed, Control + Alt + middle mouse.
And pan with middle mouse.
There's our line.
That is a one-dimensional line.
It still doesn't have any thickness.
It has no volume.
It's just a line.
You can change the parameters,
but there's really only a length.
So let's set that.
I'm going to increase that
and we can see that the light is spreading
over a larger area here, in our ActiveShade rendering.
The actual amount of illumination is constant.
We're still putting out 500 lumens.
We're just spreading that 500 lumens over a larger area.
For a realistic fluorescent light,
let's set the length to 1.15 meters and press Enter.
Now if we really wanted a realistic fluorescent tube,
then I would use a cylinder primitive, instead of a line.
Change the shape over to Cylinder.
And now we see a cylinder in our viewport
and we actually see a reflection of a cylinder
in the floor in our rendering.
We can position our view once again,
get a better look at that.
But we don't see the cylinder itself.
Unless we enable a switch here,
Light Shape Visible in Rendering.
Turn that on,
and now we actually see the light source here
in our Arnold rendering.
If we tumble in our viewport,
we'll see that there are no caps
to the rendered cylinder here in Arnold.
And we also don't see the back faces.
We just see the front faces.
For our fluorescent tube, I want a lower radius,
so we'll bring that down to 0.02 meters or two centimeters
and now I've got a realistically proportioned
fluorescent tube.
Now I could populate my scene with lots of these
fluorescent tubes,
or I could make things a little bit simpler on myself
and speed up my render times
and instead, just use a rectangle shape
and place that over the light fixtures up in the ceiling.
And that makes sense because
the office light fixtures would have some kind of
diffusion material over the fluorescent tubes anyway.
The light from raw, exposed fluorescent tubes
is pretty harsh.
So using a rectangle shape will also result
in faster render times,
because the render will not have to calculate
as many lights.
One rectangle light can substitute
for three fluorescent tubes.
Let's change our shape over to Rectangle,
and we see something pretty strange.
We're getting a rectangle here in our viewport,
but in our ActiveShade render,
we're seeing a cylinder instead of a rectangle.
Well, that's happening because we
still have the default light distribution
type of Uniform Spherical
and Arnold is interpreting that to mean
we want a cylinder,
and it's interpreting this width value
to be the radius of that cylinder.
We can adjust that
and see that it's adjusting the radius
in our Arnold rendering.
Okay for an area light such as this rectangle,
we actually want it to be one-sided
and only emit light in a hemisphere.
We don't even want the spherical distribution type.
Change that over to Uniform Diffuse
and now we see we're actually getting
a rectangle here.
We don't see it in our Arnold rendering
unless we orbit around
and look at it from the one side
in which it actually can be rendered.
It's front side.
And by the way, the front side or the renderable side,
side which is emitting light
is indicated by the sphere on the icon of the light.
So that's telling us which side is actually emitting light.
By the way, when you change that distribution type,
you may have to wait for a moment
for the viewport to catch up.
It's got to recompile all the materials
against this new light type,
and you may need to navigate in the viewport
to refresh the display.
All right, so with a Uniform Diffuse distribution type,
we're only getting light emitting on one side
of the rectangle, and that's what we want.
We can see that the illumination has changed.
We only have 125 lumens.
That happened automatically.
Okay, I want to send this light up
to cover one of my ceiling diffusion panels.
I dolly back out, Control + Alt + middle mouse
and pan around.
Turn around Edge Faces with F4,
so we can get a sense of where we are in our scene.
And I already know where I want this light to go,
so I'll just plug in the values.
I've got my Move tool still active.
We'll give it an X position
of negative 2.575 meters and press Tab.
We'll set the Y position
to 1.05 meters, press Tab.
Set the Z position to 3.985 meters and press Enter.
That sends the light up into the place
that I want it to be.
I also want to adjust the width to cover that area.
We'll set the width of the rectangle
to 0.54 meters.
And we see that it's quite dim, still,
and that's because again we only have 125 lumens
so let's bring that up to 3,000 lumens and press Enter.
Now that we have the intensity
at a physically plausible value,
we can take a look in our rendering
and it does look like the top of that white desk
is a little bit overexposed
so I can adjust for that with exposure control.
Go to Rendering, Exposure Control,
and bring the exposure value up.
Let's set that to a value of five,
which will cut the amount of light in half.
Cool, so we can close that.
By the way, if you wanted a more artistic
or realistic look to the actual light fixture up here,
then you might choose to disable
Light Shape Visible in Rendering
and instead, place some self-illuminated geometry up there.
And that would be more setup.
It would take more work and time,
but it would give you more control and better realism.
For the purposes of this demo,
I'll still use the Light Shape Visible in Rendering.
Now if you look really closely
at the edges of the light shape,
you'll see some jagged pixels.
Let's get in closer in that in our viewport
and we'll orbit around, get in real close there,
and in our Arnold rendering,
we can see that it looks really jagged.
We're getting some aliasing, okay.
So that is happening because
there's so much light coming out of that
that it's actually overwhelming
the anti-aliasing algorithm in Arnold.
So I'll get my shot frame back up again
and let that render finish.
I'll know when it's finished
when this green line reaches the bottom of the frame.
And once that's done, I want to make a clone of this window
so I can compare it to another rendering.
We've got button on the toolbar,
Clone Rendered Frame Window.
That just copies off another rendering here,
so this is the ActiveShade rendering.
It's interactive.
And here's a cloned window that's just in memory
and it's not interactive.
We can zoom in here if we want.
There's a keyboard shortcut for that,
which is Control and left mouse click.
Do that a couple of times
and on the toolbar you'll see a ratio.
We zoomed in four to one
and we can pan around with the middle mouse button.
And here, it's really clear
that we're seeing some jagged aliasing.
We can correct this using the Arnold filtering settings.
Go to the Render Setup dialog
and in the Arnold Renderer tab,
scroll down a bit.
You're looking for the Filtering rollout.
Here it is.
And we have a section for clamping.
We'll need to enable clamp AA samples.
Clamp anti-aliasing samples.
Turn that on.
That will trigger a refresh of our ActiveShade.
And we'll need to adjust the AA max value
to set a threshold,
and I've already experimented with this
and determined that a good value would be 0.1.
And now, we should get a better result.
We can close the Render Setup dialog
and wait for this ActiveShade render to finish here.
Once that is finished,
we can zoom in and examine the light fixture.
Again, control and left mouse click a couple of times
and pan with the middle mouse button,
and we can see there is a big difference here
between the version on the left
and the ActiveShade window
has the clamping enabled
and the version over here on the right
does not have clamping enabled.
We can zoom back out with Control + right click
a couple of times.
Let's go over to this view too.
Control + right click.
And compare the two renderings.
So that's how to set up photometric lights
and set their distribution type
and also how to avoid jagged aliased edges
on visible lights.