Add Calculations - Daylight Factor

Daylight Factor is defined as the ratio of illuminance at a point on a plane produced directly or indirectly by skylight to the illuminance on a horizontal plane exposed to an unobstructed view of the sky. The method only takes luminous flux from the sky into consideration (not sunlight) and is generally used with uniform or CIE overcast skies (so that sunlight and solar position is not a factor). Daylight Factor is not calculated when electric lighting is switched on in AGi32 or when sky types other than Overcast or CIE General Sky Types 1-5 are selected.

Daylight Factor ( DF) =

Horizontal Illuminance from sky light on horizontal workplane
Horizontal Illuminance from unobstructed sky

Daylight Factor is used to determine what impact the geometry of the space and location and amount of fenestration have on daylight penetration. Some uses of Daylight Factor include:


From the Add menu, choose Calculations - Daylight Factor, or from the Calculations Toolkit select image\calc_button-add_polygon.jpg.

  1. Specify a unique label up to 32 characters long. The default label will be DF_1. Unless changed, subsequent labels will be DF_2, DF_3, etc. If a number is used for the label, subsequent labels will be incremented accordingly.
  2. An optional description may be entered up to 80 characters long. Meaningful descriptions that include room information and work plane height will be useful when generating schedules.
  3. Specify the point spacing from left to right and top to bottom. By default, a point spacing of 10 by 10 is used. As the point spacing changes, the text size adjusts, automatically. You may override the text size, if desired.
  4. You may center the measurement points within the grid boundary, if desired, by clicking in the selection box adjacent to Center Points Relative to Grid Boundaries.
  5. To calculate Illuminance values at the same grid locations (for reference purposes), click in the selection box Include Illuminance Grid. This selection is enabled by default.
  6. Specify the Summary options to calculate.

Daylight Factor Options

Illuminance Options

Default Selections

  • Average Value
  • Max and Min Values
  • Percentage of Points equal to or above % of DF: User Defined; default is 2%

Other available options

  • Number of Points (If Number of Points is selected, the number of points that are in the calculation, not including points that have been removed, are shown.)
  • Daylight Factor Basis (exterior Illuminance Value)

Default Selections

  • Average Value
  • Max and Min Values
  • Avg/Min Ratio
  • Max/Min Ratio

Other available options

  • Max/Avg ratio
  • Number of Points
  • Coefficient of Variation
  • Uniformity Gradient
  1. Select the display options, including precision, text color, perimeter lines, point markers and labeling.
  2. If desired, specify Isoline contouring and/or Highlight Values by clicking on the appropriate buttons.
  3. Creation Method: Choose whether to manually create boundary lines of Daylight Factor polygon or choose an existing line, room or object as the boundary line.
  1. Click Ok. Follow the steps below depending on the selected creation method:

Specify a Polygon Manually

Create Polygon from Drawing Entity, Room or Object

  1. Locate the first point of the polygon and click the left mouse button.
  2. Move the cursor to the second vertex on the polygon and left click again.
  3. Continue in this fashion until the polygon is complete. Right click to close the polygon shape. The Daylight Factor grid will be created.
  1. Locate the pick box on the drawing entity line, object or room boundary you wish to use and left click.
  2. If a valid polygon is found (see Notes below), it will be displayed as a bold line, and the Polygon Search results dialog will appear:
  • Accept Polygon and Repeat - Select another polygon line as a template for another grid with the same properties. Use pick box to select another closed polygon.
  • Accept Polygon - Create grid using selected entity as polygon boundary.
  • Reselect Entities - Choose this option if an invalid polygon was found or if an incorrect line was chosen. Use pick box to select another closed polygon.
  • Manually Specify Polygon - Select vertices manually to specify polygon boundary, right clicking once all vertices are specified. This option is necessary if no valid polygon is found.
  • Cancel - Do not create calculation entity.

Notes:

  • Drawing Entity line segments do not need to be joined, just need to be within tolerances (2 decimals of precision - .05)
  • Line segments do not need to make a closed polygon; AGi32 will automatically close boundary line
  • AGi32 filters related lines by color.

Caveats:

  • Line segments disconnected by gap larger than tolerance level will not form valid polygon.
  • Polygons with intersecting lines will not form valid polygon.
  • Incomplete polygons are not valid and may close in an unacceptable manner.