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2 Introduction Describe Radiance system and theory. Create and simulate Radiance models via ESP-r: Generate external/internal images, Glare analysis, Generate daylight factor distributions. Control artificial lighting.

3 Physically-based rendering versus Photorealism Photorealistic images: appearance is everything! Calculation procedure compromised to produce good looking images. Unrealistic light source characteristics. Physically-based models mimic physical reality to predict light distribution.

4 Radiosity and Ray tracing Radiosity - enclosed domain, gridded surfaces. Becomes unmanageable for complex scenes due to domain discretisation. Performs poorly with specular surfaces. Ray tracing - open domain, no surface grid required. Increased complexity can easily be accommodated. Specular interactions permitted. Preferred method is ray tracing.

5 Forwards or Backwards Ray Tracing Forward ray tracing sends light from sources towards the illuminated surface or eye point. Backward ray tracing sends light from the illuminated surface or eye point back through the scene towards light sources. Most rays may never reach the area of interest in forward ray tracing. The opposite is true for backwards ray tracing - no rays are wasted as the rays start in the area of interest and work backwards towards the light sources. Backward ray tracing is preferred as it is more efficient.

6 Direct and Diffuse Light Direct light - easily traced due to known direction of beam. Diffuse light - difficult tracing due to unknown direction of travel, thus all directions have to be assessed. Direct light maintains direction and beam on specular reflections e.g. a mirror. Direct light becomes diffuse when reflected off most surfaces e.g. those painted with matt paint.

7 Luminance and Illuminance Radiance: radiant energy emitted surface. Energy units: W/sr/m 2. Luminance: light coming from surface. Photometric units: nit or lumen/sr/m 2. Irradiance: radiant energy hitting surface. Energy units: W/m 2. Illuminance: light falling on surface. Photometric units: lux or lumen/m 2.

8 Radiance Physically based backward ray tracing - quantitative answers produced. Intelligent stochastic ray tracing - more rays traced in areas of high variability. Direct model creation from CAD.

9 ESP-r/Radiance - Default external image Create a default image. 1)Select visualisation from main ESP-r menu. 2)Radiance desktop module will start. 3)Generate external view to screen.

10 Scene purposes External images - cheap and cheerful. Internal images - cheap and cheerful. Glare sources - quantitatively accurate images. Daylight factors - quantitatively accurate data. Coupling - quantitatively accurate model for lighting control. Model modified at each time step of thermal simulation. Daylight coefficients - quantitatively accurate model for lighting control. Model simulated before thermal simulation to pre-compute sensed illuminance.

11 Isolux contours Illuminance information can be displayed in a Radiance image via the falsecolor command.

12 Daylight factors Daylight Factor Daylight factor Internal Illuminance External External Sky component Reflected Component Illuminance Internal Reflected Component 100

13 Sky types Must use overcast sky to calculate daylight factors.

14 ESP-r/Radiance - Daylight factors Generate daylight factors in a zone. A grid must be defined with the daylight factors calculated at each grid point. The grid is coplanar with a surface in the zone. The grid is aligned with an edge of the selected surface. The edge is specified by the start and end vertex numbers. An iterative solution is used during which the Radiance rendering parameters are refined. The difference in predictions is calculated and the maximum for any one sensor compared against the user specified accuracy value.

15 Visual comfort

16 Lighting control