
© Next Limit Technologies 2010
Maxwell Render 2.5 User Manual
Chapter 6. Lighting with Emitters | 23
Emitter Materials are dened in a very intuitive way, using real world values like watts or
efcacy. Your emitter can be dened in three different ways:
• Custom: This option allows you to set the Color and the Intensity of your light
separately. Color can be set in RBG, HSV or XYZ scales, or correlated to a Kelvin value.
Intensity (or Luminance) can be set in a number of different ways (see next section).
You can also specify an IES/ Eulumdat le to light your scene, using measured lighting
data for different lighting xtures. These les are provided by many major lighting
manufacturers.
• Temperature: In Kelvin degrees. In the real world, the temperature of the light
source determines both the color and its intensity. Colder temperatures (near 3000ºK)
emit reddish, low-intensity light, while higher temperatures (near 9000ºK) emit blue,
bright light. This control will allow you to adjust both the intensity and the color of
your emitter with one single slider.
• HDR Image: You can use a high dynamic range image which will emit light from the
emitter surface, using images in HDR, EXR or MXI formats.
6.01 Custom
F.01 Custom
• Color: This parameter refers to the color of the light emitted. There are two ways to
specify the color:
a. Using the Color Picker: Clicking on the colored square allows the user to
choose a color in the Maxwell Render color picker.
b. Correlated Color at Kelvin Temperature (ºK): This options lets you choose
the color that would correspond to an emission in Kelvin degrees. Please note
that choosing this option will not make any changes in intensity, just color. Low
Kelvin temperatures are reddish, 6500ºK is considered white, and higher values
will produce a bluish light.
• Luminance: Species the intensity of the light. There are several options to specify
luminance, like Power & Efcacy, Lumens, Lux, Candelas and Luminance:
F. 01 Luminance types
a. Power and Efcacy: These options allow you to specify how much electricity
a light source consumes (Watts) and how efciently it converts that electricity
into visible light (Efcacy). The efcacy number species how many lumens are
emitted per watt. For example, a common 40W incandescent light bulb will have
a rather low efcacy of 12.6 lumens/ watt. This information is usually supplied
by the bulb manufacturers. A more efcient, energy saving bulb which is also
rated at 40W will have an efcacy of perhaps 17.3 lumens/ watt, so for the same
amount of energy consumed, it will emit more light. The watts/ efcacy way of
specifying an emitter’s intensity is useful if you would like to mimic common light
sources, where the manufacturer provides the watt rating and the efcacy rating.
In the “Output” row you can see how many Lumens a particular watt/ efcacy
setting will create.
b. Luminous power: Lumens (lm) is the SI (International System of Units) unit
for luminous ux. It is a common way to specify how much light is emitted. Light
manufacturers usually supply this data.
c. Illuminance: Lux (lum/m^2). Lux is the unit for specifying illuminance. It is
dened as one lumen per square meter. This is a useful setting when you would
like to increase or decrease the size of your emitter, and have it emit more or less
light. If you use lumens and scale up your emitter, the same amount of lumens
are emitted but from a larger area, giving the impression that the emitter is
weaker. If you use Lux however, the amount of lumens increases/ decreases with
the scale of your emitting surface.
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