Note: The Room Estimator is covered in more detail in the "Basic Interior Lighting" Online Learning course.

Files referenced:

Tutorial-Room Estimator.AGI

Time Estimate: 20 minutes


Room Estimator applies the Zonal Cavity method to determine the approximate luminaire quantity required to meet a target average illuminance level on a horizontal work plane in a rectangular space. At this stage, the results can be easily printed in a presentation ready format. For the purpose of this example, we will take it a step further and export the room and luminaire layout to AGi32’s Model Mode, where a calculation grid will be added and point-by-point analysis computed.

Problem Statement

Use Room Estimator to place fluorescent luminaires in a rectangular space suspended 1.5 ft from a ceiling grid to meet an average illuminance level of 40 footcandles on the workplane located 2.5’ above finished floor (AFF). The rectangular space measures 40’ x 30’ x 10’. Use the 8-cell parabolic 1X4 luminaire, zlf1, provided in the Z-Lux database.

Tutorial Summary

Step 1 – Define the Luminaire

Step 2 – Use Room Estimator

Step 3 – Export the Layout Into Model Mode

Step 4 – Automatic Placement of Calculation Points

Step 5 – Calculate


Step 1 - Define the Luminaire

Click on the New File button on the Common Toolbar to create a new job file.

The New File button on the Common Toolbar (Menu: File - New)

For this tutorial, we are going to use units of Feet and Footcandles. If you look at the Units button in the bottom right corner of the screen, it should indicate our project is set to use Feet and Footcandles (Ft - Fc). If this is not the case, click on the button and make the appropriate changes. These settings can also be accessed through Menu:Tools - System Settings - Units tab.

Units button on the Status Bar

Before using the Room Estimator tool, we must first define a luminaire. The luminaire definition includes photometric information as well as a symbolic representation of the luminaire. Each luminaire location will incorporate these parameters in addition to the aiming information specified by the user.

Within Model Mode, click on the Define button in the Luminaire Toolkit.

Define button in the Luminaire toolkit (Menu: Add - Luminaire - Define)

Access the Photometric Instabase by clicking on the Instabase button in the Define Luminaire dialog. When the Instabase In The Cloud (IITC) dialog opens, the luminaire photometric data supplied with AGi32 is available for download.

Our first step will be to set up a User Profile. This is normally optional, but it has the advantage that any Favorites or other settings that the user enables will be available from any computer by simply signing in.

Click on the User Profile tab at the top of the dialog.

Click on the link to Sign In or Create a User Profile.

In the lower half of the dialog, create a new User Profile: Enter your first and last name, your email address, a Username (anything you like), and a password that you can remember. Then click OK.

For this tutorial, we will be using luminaires from a fictitious manufacturer called Z-Lux. The luminaires and their photometric data are not real and are only accessible by entering an Access Code. This is to prevent them from being used in real lighting designs!

On the right-hand side of the dialog, enter this Access Code: pretend. Then click on the "save" icon to the right. Now you should see this:

Leave the User Profile tab and return to the View/Search tab.

Click the "Select Manufacturers" link in the upper left portion of the window. When the pop-up list of manufacturers opens, scroll to the bottom of the list and locate Z-Lux. 

Check the box and click the OK button.

The Instabase User Guide may open. It has tips for those who are new to IITC. Close it by clicking on the X in the upper-right corner. (Be careful not to close the IITC dialog!)

Now we are in the main part of the IITC dialog (View/Search tab), with the Z-Lux Sample Instabase displayed. We may now either perform a Search (using the fields on the left side of the dialog) for luminaires that meet specific criteria, or simply select the luminaire(s) that we wish to download for our project. We will do the latter.

 NOTE: If you have been in IITC and downloaded luminaires already, they will be pre-selected. You will want to unselect them to avoid downloading them again (Un-select All button at the bottom of the screen).

Under the ZL-Indoor node, in the ZL-Fluorescent group, select the zlf1.ies luminaire. You can see its characteristics shown in the image below.

Scroll to the bottom of the dialog and click Download.

The Smart Symbols dialog appears, prompting you to select an appropriate symbol for the selected photometric file.

The default Mounting Type (left side of dialog) is Ceiling Surface, which works for this luminaire.

Choose the 1x4 LV Down symbol, and then click OK.

The luminaire is entered in the Define Luminaires section. It is ready to be used in our project, except that we need to make a couple of changes first.

Begin by clicking on the Relabel button (right side of dialog). Enter a new Label: 1x4. Then click OK to return to the Define dialog.

A Description may also be entered, if desired.

Next, to set the Light Loss Factors, click on the Specify button.

In the next dialog, enter a value of 0.9 in the LLD text box, 0.9 in the LDD text box, and 0.88 in the BF text box.
Click OK to return to the previous dialog. Note that the Total LLF = 0.713.

To keep these changes to the luminaire definition, click on the Add/Redefine button.

Click on the Close button to return to Model Mode.

Step 2 - Use Room Estimator

The Room Estimator tool allows you to enter the dimensions of a rectangular room and compute a symmetric luminaire layout to meet your specified lighting criteria.

 On the Control Bar, click on the small arrow to the right of Design Tools button then select Room Estimator.

Room Estimator button on the Control Bar under Design Tools

Begin in the Luminaire Section. The Description cell is optional and will be included in the Room Description if the layout is exported to AGi32. The Luminaire Label list box contains all luminaire definitions. Since we have only defined one luminaire type in this tutorial, no selection needs to be made here.
In the Room Geometry section, specify the room dimensions: Length (X) = 40, Width (Y) = 30 and Height (Z) = 10. As the information is entered, the footprint of the room will be created dynamically in the 3D Display window.

The Suspension Length represents the vertical distance between the ceiling and the luminous plane of the luminaire. In our case, the luminaires will be ceiling mounted and are therefore assigned a Suspension Length of 0. The Work plane Height represents the vertical distance between the floor and work plane. Our work plane is located 30 inches ( 2.5’) above the floor (at typical desk height), which corresponds to a Work plane Height of 2.5, the default value.

The room reflectances are specified using decimal values between 0 and 1. By default, 0.8, 0.5 and 0.2 are specified as the reflectances for the Ceiling, Walls and Floor, respectively. To change the reflectances, click the Reflectance tab.

In the Specify section, enter 40 as the Desired Illuminance value. This value corresponds to maintained illuminance, as the total LLF entered in the luminaire definition will be considered. This value typically represents a minimum allowable average value, meaning that an average illuminance value larger than 40 fc would be acceptable to us.

In the Ceiling Grid section, click in the checkbox next to Apply to create a 2’ x 4’ ceiling grid. By default, it is specified with the 4 ft dimension along the X axis, and 2' dimension along the Y axis. To center the luminaires and the grid in the room, click in the Center selection box.

Results are calculated automatically on data entry, and the corresponding number of luminaires are laid out uniformly in the room. Room Estimator has placed a quantity of 35 luminaires in the space, which will provide an average illuminance of 44 footcandles. The luminaires are oriented and spaced according to the ceiling tile locations and to meet the luminaire's Spacing Criteria.

The Specify and Luminaire Layout sections also include information regarding luminaire spacing and Lighting Power Density. Coefficients of Utilization results can be viewed in the Reflectance tab.

The luminaire symbols included in the luminaire definition are not displayed in Room Estimator. However, their general symbol shape and scale are used in Room Estimator.

Step 3 - Export the Layout Into Model Mode

Let's assume that we have obtained satisfactory results in Room Estimator and are ready to bring the room and luminaires into AGi32 so that we may calculate point-by-point values. Remember, Room Estimator uses the Zonal Cavity method to ESTIMATE the AVERAGE illuminance level in the space. A point-by-point calculation with a reasonable number of points will be more accurate.

Click on the Export button in the Room Estimator dialog to return to AGi32’s Model Mode with the environment.

The lower-left corner of the room will be attached to the cursor. Locate the cursor at X=0, Y=0 using the mouse (it may take a zoom action with the mouse wheel) and click. OR, you may enter the coordinates of the lower-left corner of the room from the keyboard. Simply type 0,0 and press the Enter key.

Once the room location is determined, the luminaires will be placed within the ceiling grid automatically. Notice that the 1x4 symbols are now centered within the ceiling tiles.

Step 4 - Automatic Placement of Calculation Points

Once the room has been placed in the Model area, the Calculation Points-Automatic Placement dialog will appear, allowing you to place calculation points on any surface of the room or on the work plane.

To apply calculation points to the work plane, we need to highlight this virtual surface in the small graphics window of the Automatic Placement dialog. Use the Move to Workplane button (or the F6 key) to move focus to the work plane.

Click in the Calculation Points property field (currently Off), and then select On to turn the calculation points on using the current options.


Click Ok to exit the dialog.

The screen image here displays the room, luminaires and calculation points in Isometric View. Your screen will still be in Plan view, looking down from the top of the room.

Step 5 - Calculate

You should have the Calculate Full Radiosity Method button available, since it is the default setting, but if you do not, click on the small arrow to the right of the Calculate button, move the mouse down to Full Radiosity Method and click. With the Calculate button set to Full Radiosity Method, click on it to begin the calculation.

The Calculate button with Full Radiosity Method selected

The “Calculating…” dialog will appear in the lower-right corner of the screen. It displays the calculation progress as a percentage of light absorbed. The Radiosity process initially computes the direct light, that which is emitted from the luminaires directly to all surfaces. At each surface, some light is reflected and the remainder absorbed, based on the reflectance of the surface. Reflected light is then re-emitted and encounters the room surfaces again. This process repeats until all light has been absorbed (100%). The computations are then complete and the point-by-point illuminance values displayed.

While calculating, you will be given the Estimated Total Time for the calculation process, the Estimated Time Left until complete, and the Estimated Completion Time. 

The final illuminance results are displayed in the Statistics window, which will replace the calculation progress display on conclusion of the computations.


This tutorial demonstrated the use of the Room Estimator tool as a quick means of calculating average illuminance in a rectangular room with a flat ceiling. Once satisfactory results were obtained, the room and luminaires were exported into the Model Mode of AGi32. The Automatic Placement command was used to place a calculation grid within the room at work plane height.

The Zonal Cavity 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 Model Mode. The limitations of the Zonal Cavity method are as follows:

1. The luminaires must be spaced uniformly and at the same height in the room to obtain a uniform average illuminance value.

2. The coefficient of utilization (CU) calculation is based on a completely 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.

Note: If you would like to see what this project will look like when complete, you can open the Tutorial-Room Estimator.agi file, which you can download at the top of this article.