13.2.1 Introduction

Scope of calculations

The calculation engine used in Visual photometrically models The entire lighting system composed of Luminaires, Solid Objects (perhaps), and Calculation Zones. the interaction of luminaires Any light emitting object, or configuration of light emitting objects, referenced within the Luminaire Schedule in Visual. Consists of photometric, graphical, and descriptive information., sun, and sky in a user-specified environment that may consist of surfaces that absorb and reflect light which have arbitrary orientations and planar Two-dimensional in nature. All components lie within a single plane. shapes. The detail and accuracy of the photometric Referring to a data file containing information related to the photometric distribution of lighting equipment. Valid files of this type typically have a .IES extension and adhere to the format outlined in IES LM-63. model The entire lighting system composed of Luminaires, Solid Objects (perhaps), and Calculation Zones. is sufficient to predict direct and interreflected The portion of the luminous flux from a luminaire arriving at the workplane after being reflected one or more times from room surfaces. illuminances at any array of points.

Geometric input

Surfaces that block, reflect, and/or transmit light can be planar Two-dimensional in nature. All components lie within a single plane. polygons.

Photometric input

Luminaires

For electric lighting calculations, light sources are luminaires Any light emitting object, or configuration of light emitting objects, referenced within the Luminaire Schedule in Visual. Consists of photometric, graphical, and descriptive information. that have a specified luminous extent and an arbitrary luminous intensity distribution.

IES files, Elumet file, TM14 files

Luminaire Any light emitting object, or configuration of light emitting objects, referenced within the Luminaire Schedule in Visual. Consists of photometric, graphical, and descriptive information. data is assumed to be contained entirely within any of the three most commonly used data files for the transfer of photometric Referring to a data file containing information related to the photometric distribution of lighting equipment. Valid files of this type typically have a .IES extension and adhere to the format outlined in IES LM-63. information. At a minimum, these files give the luminous extent, specify which of the standard coordinate Location information usually provided in terms of (X,Y) or (X,Y,Z) components along Cartesian axes. systems is used to describe the luminous intensity distribution, list the angles of that coordinate Location information usually provided in terms of (X,Y) or (X,Y,Z) components along Cartesian axes. system that are used, and list the luminous intensity values of the luminaire Any light emitting object, or configuration of light emitting objects, referenced within the Luminaire Schedule in Visual. Consists of photometric, graphical, and descriptive information. at those angles.

The Visual calculation engine assumes that photometric Referring to a data file containing information related to the photometric distribution of lighting equipment. Valid files of this type typically have a .IES extension and adhere to the format outlined in IES LM-63. data files are in that form defined by IES/ANSI standard LM-63-02. The user interface to Visual converts any of the user-supplied photometric Referring to a data file containing information related to the photometric distribution of lighting equipment. Valid files of this type typically have a .IES extension and adhere to the format outlined in IES LM-63. files to an equivalent LM-63-02 file and submits them to the Visual calculation engine.

Surfaces

Surfaces ("solids") specified by the user are single planar Two-dimensional in nature. All components lie within a single plane. entities with a surface normal (perpendicular) derived from the order in which the user specifies the vertices The plural of vertex. of the polygon A closed planar figure composed of line segments with multiple angles and sides. defining the shape and orientation of the surface. Single user surfaces are treated in the calculation engine as two surfaces, back-to-back, separated by an internally-determined incremental distance. They are assumed to have identical photometric Referring to a data file containing information related to the photometric distribution of lighting equipment. Valid files of this type typically have a .IES extension and adhere to the format outlined in IES LM-63. properties.

Reflectance

Reflectance The ratio of the flux actually reflected by a sample surface to that which would be reflected into the same reflected-beam geometry by an ideal, perfectly diffuse standard surface irradiated in exactly the same way as the sample. is assumed to be perfectly diffuse Having hte properties of diffuse reflection or diffuse refraction. and can have values between 0.0 and 0. 999.  Reflectance The ratio of the flux actually reflected by a sample surface to that which would be reflected into the same reflected-beam geometry by an ideal, perfectly diffuse standard surface irradiated in exactly the same way as the sample. is specified in the Visual user interface in percentage form and any value specified as 100% is reduced to 0.999. Perfect diffusion permits the assumption that the amount and distribution of reflected light is independent of incidence direction.

Specular A characteristic of a surface that reflects light in a directional fashion that is often image-preserving. Gloss finishes exhibit specular reflective characteristics as do mirrors and chrome. or so-called mixed reflectance The ratio of the flux actually reflected by a sample surface to that which would be reflected into the same reflected-beam geometry by an ideal, perfectly diffuse standard surface irradiated in exactly the same way as the sample. cannot be modeled in Visual at this time.

Transmittance

Transmittance Transmission is when light passes through a material. is assumed to be either perfectly diffuse Having hte properties of diffuse reflection or diffuse refraction. or perfectly image preserving. Transmittance Transmission is when light passes through a material. can have values between 0.0 and 1.0. Transmittance Transmission is when light passes through a material. is specified in the Visual user interface in percentage form.

Perfectly diffuse transmittance permits the assumption that the amount and distribution of transmitted light is independent of incidence direction and that transmitted light has a diffuse Having hte properties of diffuse reflection or diffuse refraction. distribution.

Perfectly image preserving transmittance Transmission is when light passes through a material. preserves the direction of travel of the light, but reduces that amount. The value specified by the user is assumed to be that value of transmittance Transmission is when light passes through a material. perpendicular to the surface. If the user-specified value of transmittance Transmission is when light passes through a material. is less than 1.0 (100%), then it is assumed that glass is being used, and that the transmittance Transmission is when light passes through a material. value depends on incident angle. In this case, the calculation engine automatically determines and uses the appropriate value of transmittance Transmission is when light passes through a material. for the incidence angles involved.

Absorbtance

If the user-specified values of reflectance The ratio of the flux actually reflected by a sample surface to that which would be reflected into the same reflected-beam geometry by an ideal, perfectly diffuse standard surface irradiated in exactly the same way as the sample. (r) and transmittance Transmission is when light passes through a material. (t) do not sum to 1.0, then the absorbtance of the surface is assumed to be 1-r-t, and is the fraction of light lost by absorption in the surface.

Spectral reflectance and transmittance

The Visual calculation engine makes "the gray assumption"; that is, all reflectances, transmittances, and flux from light sources are assumed to be spectrally flat. That is, the photometric Referring to a data file containing information related to the photometric distribution of lighting equipment. Valid files of this type typically have a .IES extension and adhere to the format outlined in IES LM-63. property is uniform throughout (and therefore independent of) visible wavelengths.

Although spectral uniformity is assumed, the values of reflectance The ratio of the flux actually reflected by a sample surface to that which would be reflected into the same reflected-beam geometry by an ideal, perfectly diffuse standard surface irradiated in exactly the same way as the sample. and transmittance Transmission is when light passes through a material. are not entirely uncoupled from a surface color specified by the user. The Visual user interface estimates a wide-band reflectance The ratio of the flux actually reflected by a sample surface to that which would be reflected into the same reflected-beam geometry by an ideal, perfectly diffuse standard surface irradiated in exactly the same way as the sample. from the RGB values that define a user-specified color. If the user chooses to keep the color and the reflectance The ratio of the flux actually reflected by a sample surface to that which would be reflected into the same reflected-beam geometry by an ideal, perfectly diffuse standard surface irradiated in exactly the same way as the sample. linked, notice is given if the specified color and reflectance The ratio of the flux actually reflected by a sample surface to that which would be reflected into the same reflected-beam geometry by an ideal, perfectly diffuse standard surface irradiated in exactly the same way as the sample. are incompatible. For example, it is not possible for "brown" to have a high, wide-band reflectance The ratio of the flux actually reflected by a sample surface to that which would be reflected into the same reflected-beam geometry by an ideal, perfectly diffuse standard surface irradiated in exactly the same way as the sample..

Some surface colorizing effects can be generated in the renderings. See the section of Rendering.