Tips and Tricks for using Insight's Daylighting Analysis
This article is organized into two parts: Daylighting methodology and investigation of performance though simulation.
Before we get started, I would like to provide some background on daylighting. Daylighting is the “controlled” admission of natural light into a building for the purpose of illuminating a space. Whereas, daylight harvesting is the “controlled” admission of natural light, into a building for the purpose of reducing electric lighting and energy (kWh). For either purpose, daylighting design is defined in a range.
Investing in Daylighting
The most common lighting question the IDL receives is whether a building can achieve daylighting credits for LEED certification. It is important to ask this question early in the design process. To answer this question we can perform a cost-benefit analysis to evaluate the potential of our location/site. We will look at the following variables for our cost-benefit analysis:.
Weather or climate data will help us define the upper and lower limits of the daylight factor (available daylight). The daylight factor is the most important variable and if its average is not at least 50%, daylight is probably not a feasible method of sustainable lighting or a renewable energy resource. If the daylight factor is less than 50%, the focus of the daylighting design should shift away from supplementing lighting loads and instead focus on managing sunlight to reduce heating or cooling loads.
The most common weather file format used, for simulations, is a Typical Meteorological Year (TMY) or if you are familiar with energy/building simulations you probably recognize it as TMY3. While this is a reliable set of weather information, however, in my opinion, it lacks a crucial feature until you plug it into a software program, data visualization.
“The TMY3s are data sets of hourly values of solar radiation and meteorological elements for a 1-year period. Their intended use is for computer simulations of solar energy conversion systems and building systems to facilitate performance comparisons of different system types, configurations, and locations in the United States and its territories. Because they represent typical rather than extreme conditions, they are not suited for designing systems to meet the worst-case conditions occurring at a location. The source data are available for download from the National Renewable Energy Laboratory for download.” - NREL
A website that I prefer to use for daylighting pre-design analysis is weatherspark.com. Weatherspark is a free website that is run by Cedar Lake Ventures, a small company based in Minneapolis. It provides weather data and averages for over 145,000 locations across the globe. They offer data in two forms, tables and charts. The sections we are interested in analyzing are cloud cover, sun, and solar energy. The following charts are based on Boise, ID climate data.
Users can click on a specific range to view more detailed information as seen in figure 5 which shows the cloud coverage in Boise during June. Users may even examine data down to a single day for most charts on Weatherspark. This feature can be useful later in the design process, such as, meeting requirements for LEED V4 & V4.1 daylighting credits. While I will not go into detail on the steps to take, I would like you to be aware that using these data charts can help with determining when to run simulations under Options 2 or 3 for meeting the threshold requirements.
Figures 1 through 4, help us determine whether our site is suitable for daylighting. Figures 2-3 show there is 8 to 16 hours of daylight per day available in Boise is when the most daylight is available as a resource for lighting or renewable energy (between March and September). Figure 3 shows the value of daylight throughout the year. So while there is an average of 15 hours of daylight available in June, only about 8 hours is considered high quality daylight.
Lastly, we must examine cloud coverage, figure 1. It was determined that our daylighting strategies should be considered in the months of March until September, however, when we also consider cloud coverage, we see that our range of effective daylighting is shortened to June until September. Therefore, I would not recommend investing in the daylighting strategies past the standard side lighting (windows), however, this is not say that any daylighting strategy would not work but rather that the rate of return for implementing skylights or clerestories with photocontrols would be negative. Therefore, the payback is too far away to be treated as a incentive.
Cloud coverage or sky conditions are divided into three categories; Overcast, Partly Cloudy, and Clear.
- Overcast – the sun’s position can not be determined because of the cloud cover density and light is diffused evenly across the sky dome.
- Partly Cloudy – overcast skies that have a few clear spots and mostly clear skies that have a few clouds.
- Clear – With the exception of the sun a clear day is less bright than the overcast sky. Illumination is dependent upon the sun’s position, the season, and water vapor in the atmosphere.
What happens if the answer to our question, investing in daylight, is yes or maybe your client is insistent on implementing daylighting in the building? Well, the next step is to take our data and apply it our site’s context as well as building type or characteristics.
It is important to understand your site as it will provide you with data to help you get started. For example, what strategies, if any, are the surrounding buildings using, but also, note the orientation and width. If possible, conduct a survey/study of the surrounding buildings. Your building should take advantage of the sun path as relative to the Latitude & Longitude, however, other site conditions such as circulation, wind, and obstructions should not be disregarded. The easiest and, in my opinion, quickest way to analyze your building’s exposure to daylight on the site level, not the city, is to create a Sun Path Diagram, as seen below in Figure 6.
“The sun path diagram for a given latitude can be used to determine the sun’s position in terms of altitude and azimuth for any hour of the year. The same diagram of altitudes and azimuths may also be used to describe the position and size of objects from a particular viewpoint on a site.” The book Sun, Wind, and Light by Brown and Dekay is considered by some to be old fashioned but I still see this as a valuable resource. Sun, Wind, and Light explains concepts in a step by step manner that is easily digestible. The intention of the sun path diagram is to inform us of the sun’s position throughout the year as well as time of day so we can account for the change in the incident angle from a solstice to equinox and back again. Use this data to inform your exterior louvers, light shelfs, window placement, window to wall ratio, and potential landscape design decisions.
You can optimize a building’s footprint for daylighting by limiting floor plate depth (north to south) as there are limitations to how far light can be distributed. To see a visual demonstration of this concept please refer to our daylight pattern guide here: http://idlboise.com/content/daylight-pattern-guide
So we have our location data, cost-benefit analysis, site context with data analysis, and a few rough estimates or design ideas that we would like to use. The next step is to evaluate the performance of those rough estimates or design ideas by performing a simulation.
Insight's Daylighting Interface
All settings, features, and workflows are based on using Revit 2020
Modeling is an aspect of the design process that in recent decades has undergone rapid change as well as adoption by multiple disciplines that help shape the built environment. Many would say the adoption of new modeling methods were a result of disciplines wanting to achieve an Integrated Design Process. However, while that result is an ideal goal shared by many it overlooks the economic viability that each new model methodology facilitated by reducing time and money expended on a project through accurate cost estimation and decreasing the request for information or reworks.
Energy modeling software is often too complex for architects to use during the early stages of design, resulting in building performance analysis being performed at later stages. Furthermore, the Architectural profession lacks established methodologies and protocols that incorporate performative analysis into the early stages of design. Design decisions that have significant impacts on building performance are made at the pre-design/schematic phase of a project. (Massing, Orientation, Volume, Shading, Daylight strategies, etc…)
“The point from day one is not to quantify the amount of energy…” but rather provide the opportunity to “enable a conversation with the Architect, Engineer, and Client” – Ian Molloy
Setting up your model
In all simulation software programs, there a minimum threshold you must meet in order to run a simulation, i.e., you must have a space defined by having a floor, walls, roof, etc. Here are the minimum requirements needed to run a daylight simulation in Insight:
You must have these in your project in order for the program to create a copy of your model to perform simulations. While these building characteristics are important, the first step you should do when creating a model is to set your location. Setting your location will save you headaches down the road when you are inputting your simulation settings, but also, ensure the program pulls the correct data, such as, weather data, when running a simulation. After you have installed Insight for Revit you will find the plugin under the Analyze ribbon, figure 7. To access settings for Insight you will need to be logged in with your Autodesk account as the feature is a cloud based subscription service.
Setting your location and weather files in the energy settings will also be applied for all settings related to simulations. Once you type in your site’s address or drop a pin on the map you will be given list of weather stations near your site (figure 8 & 9).
To have a space or ‘Room’ be included in your simulation you will need to confirm this in your room schedule, figure 10. All you have to do is have the box checked under the ‘Include in Daylight Simulation’ column. Also, after you have run a simulation you will be able to access a Insight Lighting Room Schedule, figure 11. The ‘Include in Daylight Simulation’ for this schedule will allow you to omit spaces from being displayed or to remove spaces from your calculations without running another simulation.
Material specification is an important facet of any design but is absolutely crucial when considering daylight design. Revit has not always been concerned about simulations, but rather, in it’s early years was concerned about rendering or how realistic could we make the project before construction. Therefore, some features of Revit may seem intuitive, however, they are not functional when it comes to simulation settings. For example, the ‘Analytical Properties’ section in the type properties will not affect lighting analysis as these are intended for energy analysis. To set parameters for illuminance analysis you must use the ‘Appearance Tab’ in the material browser, FOR ALL MATERIALS.
In Revit there are multiple places to edit material properties but for illuminance analysis please use the following steps.
- 1. Select the object you want to edit.
- 2. In the properties pane on the left, navigate to the ‘Edit Type’ button and click it, figure 12.
- 3. This will open the ‘Type Properties’ menu. From here, figure 13, to change the material of a non-window object you can click ‘Edit” under Value for the ‘Structure’ parameter.
- a. Once you have the ‘Edit Assembly’ menu open click the three dots for any portion of the structure under the ‘Material’ column.
- 4. If your object selected was a window or glazing then you will also bring up the ‘Type Properties’ menu but you will able to go directly to the ‘Material Browser’ from here.
- a. Click on the material under the ‘Value’ column and three dots will appear on the right edge of the boundary.
- b. Select the three dots.
This is the material browser, figure 14, and here you can edit almost all options of materials, including making your own. One tip I do have if you are going to be editing in the ‘Material Browser’ is to ALWAYS COPY FIRST, edit second. At the bottom of the screen on the left hand side you will find a symbol that is a ball with a plus sign. Clicking this while having your material selected will allow you to duplicate it and preserve the standard Autodesk material file. If you forget to do this and edit some of the original materials but want them back to the default settings you can uninstall your material library and reinstall the default one that comes with Revit. Remember we are only concerned about the ‘Appearance’ tab as those options will affect our illumination analysis.
The material properties of glazing that we are interested in has to do with Visible Light Transmittance or Visible Light. For example a VT .67 would allow 67% transmittance of light. This method only partially works for Revit and goes to back to something I mention earlier, the intention of Revit, originally, was to create a realistic building without actually building it. Without knowing it AutoDesk created a perfect software program for predictive analysis with Revit’s BIM infrastructure but again, that was not the intent. Therefore, we have two options for setting our windows/glass panes VLT in Revit for illuminance analysis, RGB and VLT. Now I would strongly encourage you to stick with the first option of RGB and hold off on using the latest update where you are allowed to input a numerical value for VLT.
Option 1 - RGB (For Insight lighting v3 and previous
Here is a link to a document that deals with FAQs regarding Insight Lighting Analysis and has a good explanation of converting RGB to VLT:
Now you are probably wondering how setting the color, RGB, of your window/glass pane will affect its VLT. Well I would like to introduce you to Revit’s RGB to VLT conversion table that will allow you to specify the VLT properties for objects in your building. To use this table please do the following:
- 1. Have selected a transparent material/object within the material browser.
- 2. Under the appearance tab change the color to custom.
- a. You can ignore the reflectance option as it is not used for simulation.
- b. Also ignore the sheet of glass. Revit will pull this information from the window geometry itself.
- 3. To determine what values to assign to RGB refer to the table above with consideration towards the number of panes and the thickness of each pane.
- a. Rows – Modeled thickness of glass panes and the number of panes modeled in Revit.
- b. Columns – Desired visual transmittance or Tvis.
For example, a double pane window with each pane being 5mm thick and Tvis of 60% would have the RBG value of R44, G44, and B44. If you are interested in learning more about how this option’s value are determined please refer to the link above.
Option 2 - RGB and VLT (For Insight lighting v4 and beyond)
Please note, as mentioned above, that this setting is still being actively worked on and you are responsible for verifying any results from simulations using this option. One of the reason why I can’t tell you when this option will be fixed is that AutoDesk uses a proprietary simulation engine for performing illuminance analysis and therefore I don’t know what they are running under the hood or any progress that has been made.
What I can tell you is that Option 1 – RGB is based on AutoDesk’s v1 cloud rending engine and in 2019 AutoDesk announced they would be releasing v2 of the cloud rending engine. All version of Insight Lighting v4 and forward will be using Option 2 to determine VLT for windows/glass panes.
“The Glazing Visual Transmittance calculation has been significantly simplified, while adding some additional capabilities. RGB and VT have a simple linear relationship, and thickness of the modeled glass element no longer needs to be considered, so a material can be applied to any model element, and it will yield the same visual transmittance.” – AutoDesk Forums (https://forums.autodesk.com/t5/lighting-solar-analysis-forum/critical-up...)
‘Reflectance’ has also been updated to consider using a value from window specs or the default range 5-15%. In either case I would recommend leaving this setting at its default value. In addition, ‘Sheet of Glass’ will affect the Tvis and will have a default value of 2 which assumes a glazing unit is 2-sided. Lastly, if you are using an old material library then you will have to use this updated conversion of RGB to VLT: VT = RGB/255
So, to clarify, if you are using Insight Lighting v4 or later then you will be following Option 2 for setting your Tvis by either using the new RGB to VLT conversion on old materials or by specifying the VLT of the material in the appearance tab. Moving forward AutoDesk will be retiring the old materials, which you can identify by a yellow caution icon in their thumbnail image, and will be introducing ‘New Glazing Appearance Assets’. The new glazing materials are available in the materials libraries from 2019 and 2020, however, you will need Revit 2019.2.2 and 2020.1 or later to resolve an issue that arose from having two separate libraries and simulation engine in a single software program. You have the option to update your materials manually by using the ‘Asset Browser’ and using the two way arrow icon to swap out materials. Basically, at this time Insight Lighting is undergoing a major infrastructure changes and there will be some growing pains associated with switching to the new materials, engine, and simulation settings but, in my opinion, it will be worth it.
Notable highlights about these new glazing materials include a new setting in the appearance tab to directly set VLT, display images of glazing material will update to reflect changes, and you can now specify diffuse or fritted properties to windows/glass panes. If you would like a more detailed explanation you can visit the following forum post: https://knowledge.autodesk.com/support/revit-products/learn-explore/caas...
The menu for the lighting aspect of Insight is very different than the energy portion. The figure below shows the default menu where you have to choose either ‘Run New Analysis’ or select a previously run simulation from the drop down menu.
If you select 'Run New Analysis' then you will be redirected towards this menu:
You are given two drop down menus, Analysis and Levels. Levels represents which floor you would like to include in your simulation run and with analysis you have the options of running one of the following simulations:
In your model that will be used for simulations I would recommend that you change your levels to ground floor, first floor, second floor, etc… to avoid confusion and wasting any cloud credits used for running simulations. The simulation option you select will affect the remaining options, Environment, Illuminance Settings, and cloud credits by either expanding available options or auto-filling settings. For example, you will only be allowed to edit the ‘Environment’ section if you have Illuminance Analysis or Solar Access selected.
This section allows you to edit the type of sky model used for simulation as well as specifying exactly when you want your simulation to run regarding to day and time. Under Illuminance Analysis you are given the options of choosing your sky model, two dates and time to specify, and if you would like to use weather data. You should always leave this option ‘Use Weather Data’ checked. The following sky models are available for you to choose:
CIE is the commission international eclairage that has developed a series of mathematical models of ideal luminous distribution under various sky conditions. The other two major sky models commonly used for daylight simulations are Perez and Reinhart.
The Illuminance Analysis simulation is intended to give you a snapshot for how your building performs in regards to daylight performance. Therefore, the environment settings for this simulation are limited to two days and points in time for the days selected. Sidenote, this simulation is ideal for determining if your building will meet LEED standards for options 2 or 3.
For all other simulation, other than Solar Access, the Environment section will be grayed out and you will not be available unless you choose to override the settings.
The action of illuminating; decorative lighting or lighting effects. Expressed as luminous flux per unit area on an intercepting surface at any given point. Whereas a Lumen is the photometric unit of light output and is defined as amount of light given into one steradian by a point source of one candela strength. There are many units or standardization of light as a measurement but which on you use will depend on the application.
In the Architectural Engineering and Construction (AEC) industry we typically follow two units, Lux and Foot-candles, as well as, various standardized methodology. One of the earliest and still fairly common standardization is Daylight Autonomy. Daylight Autonomy is an Annual daylight metrics that is expressed as a percentage (%) of annual daytime hours for point(s) in a space that are above a specified illumination level. It was first proposed in 1989 by Association Suisse Des Electriciens (French version of IES-NA). However, it was enhanced by Christoph Reinhart between 2001-04 by considering the geo-location specific weather data for an annual basis. This updated version has become the industry accepted standard as well as being adopted by LEED in version 4 and is referred to as Spatial Daylight Autonomy.
Why do we use sDA?
For more information about sDA and ASE please refer to IES LM-83 or LM-83-12.
The figures below show the two types of settings that will be available to you. Both menus are similar in that you will be able to set the minimum and maximum thresholds and how your sensor grid will be set-up. You can still change the thresholds for sDA and ASE but the defaults will be set to meet the criteria for LEED v4 daylighting credits.
Revit’s Insight as well as the lighting analysis portion simulations are performed in the cloud. The time to complete a simulation depends on a handful of factors such as computational power, density of information, and project size. Therefore, Autodesk’s simulation programs utilize the cloud for performing simulations. While this may be a faster and more efficient method to conduct simulations, it does however come with a monetary cost. You will need to purchase ‘Cloud Credits’ from Autodesk to access the cloud server for simulations. Some additional settings under this section:
Running a Simulation
Once you have the settings configured for your simulation you can run your simulation by pressing ‘Start Analysis’.
Once you press ‘Start Analysis,’ the menu will be replaced with a new menu stating that your model is being uploaded to the cloud. After you hit okay, another menu will appear and ask you if you want to save your project.
After you click okay, you will be redirected back to the previous view. The simulation will run in the background so you can continue to work on your project. Once the simulation is complete you will be prompted by this menu:
I would recommend selecting the first option so that any work you were doing while the simulation was running will be saved.
Analyzing your simulation results
After you accept, update and save your project you will have a Insight Lighting Model View tab in your project space. This view is where you will be able to interact with the simulation results for your project, but first you will receive an overview of your results. You can document this now or revisit this menu later on.
To get past this menu you have to hit the X in the top righthand corner. After that you will be directed to an ‘Insight’ version of your 3-D view or floor plan. If you look at your properties menu on the left, figure 30, you will see the following new options have been added, ‘Default Analysis Display Style’ and ‘Analysis Display Settings’. The ‘Default Analysis Display Settings’, figure 31, will allow you change the color scheme, scale, and units of your results. You can use styles from the list provided or you can create your own to suit your needs. The ‘Analysis Display Settings’, figure 32, will give you an overview of your settings and will also allow you navigate to the default display settings. The ability to change your color scheme and scale of your results will allow you convey different levels of information, such as quality of light, glare, or investigate various levels of illuminance uniformity.
If you click on the lighting plan, your properties menu will be changed to show additional analysis results.
- Data sections
- a. Analysis configuration – select which simulation you would like to display. For example, if you ran a simulation on one floor at 9am and 3pm then you will be able to select one or both data sets to be displayed.
- b. Data Range – will display current data or all data. I would recommend leaving this setting on current data range.
- a. Results visibility – will open the analysis results settings.
- Overall Legend
- a. Show configuration name – show legend label or uncheck to hide.
- b. Show description – will display the description if you have one or uncheck to hide.
- c. Overall legend text – allows you to change the font size of the legend labels and name.
The final step in the analysis process is to export your results for either documentation or conveying information to your client, i.e. Architect, Owner, or Facilities Manager. You are able to export your ‘Insight Views’ as you would a normal view Revit if you prefer a visual display of your results. In addition, if you navigate to the Insight Lighting menu, figure 18, and select a simulation run but instead of hitting go you would need to select ‘Export’ in the bottom left hand side. You are able to export your results in the following formats:
The simulation process is iterative. The process takes snap shots of your building’s performance at a moment during the design process. These iterations are used to inform design decision that will affect the building performance and overall direction of the project. If you would like to know more about this process we did a BSUG lecture on this topic and you can find it here: https://www.youtube.com/watch?v=9K-k5Fh7m1M&list=PLURsSHj3SumC2ic16NTSHz...
After earning a Bachelor of Science degree in Architecture from the University of Idaho, Moscow, Dylan studied the science and engineering of building design by completing a Master's degree in architecture. As a student he worked at the Integrated Design Lab and gained hands-on experience in the practice of Integrated Design. As an IDL Research assistant, Dylan worked with both the architectural and engineering side of integrated design, providing a broader opportunity to cross over fields of study. He started working on real world projects at the Lab in the spring of 2015 and, graduated with a Master's of Architecture in Fall of 2017 with an emphasis in urban planning and net-zero/energy efficiency building design. Shortly after graduation Dylan began working as a Research Assistant at the IDL and has since been working on a wide range of projects from Energy Modeling to Daylighting Design.