Room Estimator - Concepts

AGi32 provides a quick design tool for interior spaces using the IES Zonal Cavity method, called Room Estimator. Use Room Estimator to determine an approximate number of luminaires required to meet a specified average level of Illuminance on a workplane or floor or based on a maximum LPD (lighting power density) specification. Room Estimator will also reverse the process and calculate an estimated average Illuminance level  and LPD based on a set number of luminaires.

Once the basic inputs have been entered (room size, reflectances, luminaire label), Room Estimator will show you the calculated results immediately as you interact with the dialog. This functionality allows you to change any of the variables used in your analysis while the results are continuously and automatically updated. You may create up to three different room layouts in Room Estimator at the same time and compare their results.

Once the luminaire quantity has been determined, you may export your results to AGi32's Model Mode and let Room Estimator automate the process of room creation, grid creation, and luminaire placement. The Automatic Placement command will open, allowing you to set the point spacing. Once you have returned to Model Mode, you may calculate point-by-point Illuminance values in the room by simply clicking the Calculate button on the Switches toolbar.

IES Zonal Cavity Method

The IES Zonal Cavity Method (also known as the Lumen Method) is used to calculate average illuminance on a work plane in an interior space. AGi32 provides the Room Estimator tool as a quick means of calculating average illuminance in a rectangular room with a flat ceiling.

The average illuminance on the work plane is defined as:

E (average, maintained) = [(lumens per lamp) x (lamps per luminaire) x (number of luminaires) x CU x LLF] / [work plane area]

If the desired maintained illuminance is known, the equation may be solved for the total number of luminaires:

Number of Luminaires = [E (desired, average, maintained) x (workplane area)] / [(lamps per luminaire) x (lumens per lamp) x CU x LLF]

This method has some limitations that may cause the average estimated illuminance value to vary from one obtained by averaging individual point by point calculations (in AGi32). The limitations are as follows:

  1. Luminaires must be spaced uniformly and at the same height to obtain a uniform average illuminance value.
  2. The coefficient of utilization (CU) calculation is based on a completely empty room. Adding objects in the space will completely change the average value from that derived in an empty room.
  3. The average Illuminance calculation is defined as the total number of lumens reaching the work plane divided by the area of the work plane. This is a simplified method of calculation and results will generally be higher than the average calculated from a set of discreet measurements as is the case in point by point calculations. Point by point calculations will always be more accurate than the average method resulting from the IES Zonal Cavity calculations and will generally be lower (by approximately 10% in most cases).
  4. Room reflectances are based on grayscale color values.

Room Estimator Metrics

All calculations are based on the published IESNA Zonal Cavity Method and associated algorithms.  Results are calculated from the content of manufacturer photometric files.

Light Loss Factor (LLF) - LLF is a multiplier used to simulate a reduction in lighting system effectiveness due to factors such as dirt accumulation (Luminaire Dirt Depreciation, Room Surface Dirt Depreciation), depreciation of lamp output over time (Lamp Lumen Depreciation), ballast performance (Ballast Factor), and others. These factors are multiplied together to achieve the total Light Loss Factor. Consult the IES Lighting Handbook for details about how to determine the LLF for different luminaires and lighting applications.  This metric is extracted from the selected luminaire's definition.

Luminaire Orientation - The horizontal rotation angle (about the Z-axis) of the zero-degree photometric plane as measured counterclockwise from due east (X-axis, 0 degrees). All luminaires are placed using a zero degree orientation by default. Users may also enter an alternate Orient Angle of 90, 180 and 270 degrees if desired, to better align luminaires within the geometric constraints of the room.

Calculated Average Illuminance - This metric may vary from the desired Illuminance value. The variation is resultant from the calculated number of luminaires generated and generally depends on the specified room size and ceiling grid.

Calculated Number of Luminaires - Room Estimator generates a uniform grid of luminaires using the room geometry, luminaire spacing criteria, and end spacing requirements. This number may vary from the luminaire quantity entered. For example, if you request a layout using 27 luminaires, Room Estimator may calculate a grid of 5x6 luminaires (30 total) depending on the room geometry and ceiling type.

Luminaire Locations and Spacing - Luminaire layouts begin from the lower left corner of the room. End spacing refers to the distance from the first luminaire's insertion point to the wall.

Luminaire Suspension Length - This metric is obtained by deducting the ceiling cavity height, if any, from the room's height.

Lighting Power Density - This metric is calculated using the watt value specified in the selected luminaire's definition.

LPD = [(Watts per Luminaire) x (Number of Luminaires)] / [Room Area]

Room Cavity Ratio - The RCR describes the radiative exchange between the ceiling cavity and the floor cavity. The effective reflectances of the cavities are used as the reflectances of the rectangular space. If there are no cavities in the layout (surface mounted and recessed luminaires and a work plane on the floor), the RCR describes the radiative exchange between the base and top of the room. This number is used when finding the Coefficient of Utilization.

Coefficient of Utilization - The CU describes the fraction of lamp lumens that reach the work plane directly from the luminaire and via interreflections.  It takes into account 'room efficiency', luminaire efficiency, and luminaire photometry. This value is valid for empty rooms exhibiting perfectly diffuse reflectance.

Effective Cavity Reflectances - Single reflectance vales that give the combined reflectance effect of the ceiling cavity and floor cavity. The ceiling cavity is bounded by the room walls, the ceiling, and the luminaire plane (suspension length). The floor cavity is bounded by the room walls, the floor, and the work plane. Effective cavity reflectances are applied at the opening of their respective cavity and are used to determine the Coefficient of Utilization.

Estimated Average Illuminance (E) [fc, lux] - Total lumens reaching the work plane divided by the area of the work plane. This value is valid for empty rooms exhibiting perfectly diffuse reflectance. This value might vary considerably from that obtained by averaging discrete values of Illuminance at several points.

Lighting Power Density (LPD) [W/ft2, W/m2] - Total wattage of all luminaires within the room divided by the area of the room.

Room Cavity Ratio (RCR) - Ratio indicating room cavity proportions based on the perimeter and height of the room cavity. The room cavity is bounded by the walls of the room, the work plane, and the luminaire plane (suspension length). RCR is used to determine the Coefficient of Utilization.

Spacing Criteria - An interior classification calculated for luminaires with > 60% downlight, describing the maximum limit of luminaire spacing. The criterion is defined as the ratio of luminaire spacing to mounting height. Two criteria values are displayed; one for the 0-180 luminaire axis and one for the 90-luminaire 270 axis. With a Luminaire Orientation angle of zero degrees, these axes correlate to the Columns and Row layout in the room. However, if the luminaire Orientation angle is specified as 90 or 270 degrees, the Spacing Criteria ration will switch as well. When the calculated spacing to mounting height ratio exceeds the recommended criteria, Spacing Criteria is displayed in Red; indicating possible inadequate overlapping of light from adjacent luminaires.

Maximum Recommended Spacing  =  SC * (MH  -  WP), where

SC  =  spacing criteria

MH  =  height of the luminaires above the floor

WP  =  height of the work plane above the floor.

3D Interactive Display

Navigation Modes

Orbit  - The focus and the focal distance remain fixed while the eye moves (changes the view direction about the focus).

Walk - You may move forward, back, and turn left and right. The focal distance remains fixed while the eye moves.

Zoom - The focus remains fixed while the eye moves (focal distance changes along the view direction).

Default Views

The following default views have been implemented.  All default views zoom extents with the focus at halfway between the minimum and maximum extents.

Mouse & Keyboard

The mouse is used to navigate (using the current navigation mode) by left-clicking and dragging (while pressing the left mouse button) the mouse up, down, left, and/or right. The navigation speed is increased by dragging the mouse cursor farther from the click-point and decreased by dragging the mouse cursor closer to the click-point. When the left mouse button is released, navigation stops. The mouse wheel and keyboard keys may also be used to navigate in the 3D display.

Mouse: You may Zoom In and Out by scrolling your mouse wheel up and down.

The following keystrokes affect navigation control: