Who is this for: Architects and engineers interested in daylighting and artificial lighting illuminance renderings.
Takeaway: Learn about Illuminance renderings which are used to help understand if the space is adequately light for its intended use.
By: David Scheer – Green Building Studio Product Owner
Autodesk 360 Rendering Illuminance
Autodesk 360 Rendering enables you to render visual and illuminance images using the Autodesk cloud, leaving your own computer resources free to help your organization work faster and smarter. Some of the capabilities of Rendering in Autodesk 360 include:
- Solar studies of designs in progress showing the effects of insolation and shading during the day.
- Panoramas of your scene, allowing you to navigate through the scene interactively.
- Apply background environments to rendered scenes.
- Illuminance simulations of scenes, to quantify the effects of natural and artificial lighting on rendered surfaces or points in your scene.
Above: Render in the Cloud option under the view menu in Revit and Vasari
In this article, we will talk about the concept, architecture and technology behind the Autodesk 360 Rendering service. For even more information, visit the Rendering wiki help site. There is also a very nice introductory article here by one of our German partners, and you can find a great intro video and tons of other resources at the Autodesk 360 Services & Support site. You should also take a look at our previous two posts on using Autodesk 360 Rendering and Revit/Vasari for the creation of illuminance images.
The role of illuminance in lighting and daylighting design
What is ‘illuminance’?
A ‘visual’ rendering of a scene, which is what you would see with your naked eyes, is a way of mapping the ‘luminance’ of the objects in the scene. Luminance is simply the intensity of light reflected off objects in a scene and reaching your eye. When mapped with color and texture patterns we can create a rendering that shows the quality of the luminance and therefore how we see the world.
While luminance is really useful for understanding qualitative measures of the success of a design, it is not a good measure of light quantity. Because the human eye can adjust for a huge range of illumination levels over 3-4 orders of magnitude, from bright daylight in the 10’s of thousands of lux (1000’s of fc), to mere 10’s of lux (single-digit fc), a visual rendering of a bright and a not-so-bright space are difficult to measure. Can you tell by looking at the visual renderings that there is over 100 times more light intensity on the wall in the day image than in the night image?
Visual rendering Illuminance rendering
Visual rendering Illuminance rendering
Visual and luminance renderings are useful for understanding qualities like light distribution and glare, but not for understanding if the space has enough light for its intended use.
For light to be reflected off of an object (luminance), it has to have light illuminating it in the first place. In lighting and daylighting design, ‘Illuminance’ is one of the quantitative measures we are interested in, because this is the light that makes the space usable by people with eyesight. This is the light that illuminates a desktop so we can see our work, a white board so we can read drawings, a hallway so we can navigate without bumping into walls and people.
Illuminance is a measure of light available at a particular point in the scene. We normally visualize this quantitative value using a color scale that represents the amount of luminous flux, or the ‘lux’ falling on that point (lux is the SI metric equal to about 10.76 foot-candles (fc)). Rendering automatically formats the color scale with 10 subdivisions between 0 and maximum level in the scene.
With the illuminance mapping available from the Rendering service, you can now see the actual value of useful light falling on critical surfaces like desks, walls and walking surfaces. Depending on the levels of illuminance required for a particular use or activity, you can use these quantitative renderings to understand whether the space is useful or if the design needs more attention. How well does the space below perform under daylight and night light?
Luminance (Visual) Rendering – Daylighting only
Illuminance Rendering – Daylighting only
Luminance (Visual) Rendering – Electric lighting only
Illuminance Rendering – Electric lighting only
- Conference areas – 20-50 fc (215-540 lux)
- Lobby and Reception – 0-20 fc (0-215 lux)
- School reading areas – 20-100 fc (215-1080 lux)
- Hotel corridors – 10-20 fc (110-215 lux)
Other metrics that can be calculated using illuminance include the new IES Spatial Daylight Autonomy (sDA) and Annual Sunlight Exposure (ASE) standards for daylighting performance, which you can read about here, and qualification for LEED IEQc8.1 – Daylight and Views – Daylight:
Demonstrate through computer simulations that 75% (90% for schools) or more of all regularly occupied spaces achieve daylighting illuminance levels of a minimum of 25 footcandles (fc) [270 lux] and a maximum of 500 fc [5400 lux] in a clear sky condition on September 21 and 9 am and 3 pm.
Tell Us what you think: What other lighting and daylighting workflows would you like to accomplish with this service?