For example, if the HDR pixels were thought of as a filter and those pixels ranged from 0 to 1.0 with the sky set to an intensity of 1000 cd/m2, the resulting luminance would be 1.0 * 1000 cd/m2.įor Emissive Materials applied to Static Meshes that enable the per-Actor settings Use Emissive for Static Lighting, the luminance of the surface is used to bake lighting into the scene.įor Point, Spot, and Rect Lights, you can specify the unit type of any Light that has Inverse Squared Falloff enabled. Sky Lights use the pixel intensity multiplied by the light intensity result in a total luminance that is expressed in cd/m2 in HDR. It is expressing the total amount of light falling on a surface.Įmissive surfaces are expressed in Candela Per Meter Squared (cd/m2) which specifies the pixel luminance before any lighting is added. Unitless is an engine-specific light intensity value and maintains compatibility with engine releases prior to Unreal Engine 4.19.ĭirectional Lights are expressed in Direct Normal Illuminance or Lux (lx) which represents the Illuminance produced on the earth by the visible part of the direct solar radiation on a surface perpendicular (or normal) to the Sun's rays. No matter its distribution (wide or narrow spot), the total amount of energy emitted will be the same. In photometry, luminous flux (or luminous power) is the measure of the perceived power of light. Lumen (lm) is a measure of the luminous flux emitted into the angle of one steradian.
For example, a light set to 1000 cd would measure 1000 lux at one meter. Point, Spot, and Rect Lights can select between the following lighting units:Ĭandela (cd) is a measure of luminous intensity emitted uniformly across a solid angle of one steradian (sr).
Sky Light and Emissive Materials as Static Lights use Luminance expressed as Candela per meter squared (cd/m2). Between the physically based units for lighting and auto exposure, creating realistic lighting is much more achievable without "magic" numbers and artists having to "eyeball" different values.Įach type of light displays its physically based lighting unit next to its Intensity value in its Details panel when selected.įor these types of lights, their intensity is displayed as follows:ĭirectional Light uses Direct Normal Illuminance, expressed as Lux which is equal to one lumen per squared meter. In addition to light types supporting different lighting units, Post Process for Eye Adaptation (or Auto Exposure) now supports an extended range of values and is expressed in EV100 (ISO 100). Lights in Unreal Engine (UE) are defined using physically based lighting units, making it possible to enter known, measurable values to achieve fully realistic lighting.
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