Helping create a more sustainable future.

Sun Simulator


Sun Emulator


Table Top Heliodon

What is a Heliodon?

A heliodon is a device that simulates the angle at which sunbeams strike a physical model of a building or landscape.  All heliodons consist of one or more light sources and a mechanism to support the model and to rotate it through one to three axes.  Since the three variables of latitude, time of year, and time of day determine sun angles, a heliodon must be adjustable for all three factors.


Many different types of heliodons exist but most utilize one light to simulate the sun. If the light source is fixed as in the case where the lamp is fixed on the ceiling or where the actual sun is used, the model must be rotated to account for the 3 axes. Most heliodons simulate sunbeams by a combination of moving the light source and rotating the model.


Only a few heliodons exist where our everyday experience is simulated by the model being fixed in a horizontal position and the light moves along three axes to adjust for all 3 variables. The advantage of these types of heliodons is that they make it much easier to understand the motion of the sun and the resulting angles of sunbeams.  Therefore, these devices are called “conceptually clear heliodons”, since they allow easy understanding of solar geometry and its impact on buildings and cities.  To learn more about conceptually clear heliodons, click on the Sun Simulator or Sun Emulator images above.


Although the Table-top heliodon is not a conceptually clear heliodon, it is also presented because it is extremely cheap, small and precise.  To learn more, click on its image above.

Successful solar responsive design requires a thorough understanding of solar geometry and its impact on design.

Why Heliodons?

Energy consumption is the primary cause of climate change, and buildings use about 50% of all the energy consumed in the United States. Thus, buildings are the main cause of climate change, and they use energy primarily for heating, cooling, and lighting all of which are all greatly impacted by the sun.  Solar responsive design can significantly reduce this energy demand by harvesting the winter sun for heating, by rejecting the summer sun to reduce the cooling load, and by collecting a small amount of quality daylight year-round to replace most of the electric lighting used during daylight hours.


Successful solar responsive design requires a thorough understanding of solar geometry and its impact on design.  Heliodons can teach developers, builders, and architects the basic concepts that will allow them to design low-energy solar-responsive buildings and communities. Heliodons can also convince potential owners to request solar responsive design and then see the validity of a particular design. They are powerful tools for demonstrating the potential and logic of solar responsive design to people of any age or education level.


There is a widespread belief that because of the existence of powerful computers and sophisticated software, it is no longer necessary to use physical modeling to understand and design solar responsive buildings and communities.  Although digital simulation has now been available for many years, new buildings reflect little use of solar responsive design and when they do, the designs are often faulty.  The old computer adage of “garbage in - garbage out” may explain the lack of success.  It is necessary for the designer to have a good understanding of solar geometry and the intricacies of solar strategies before the computer can be successfully used.  Consequently, it is most effective to first use the heliodon for the basic understanding, and only then use computers to design solar responsive buildings.

What is your Solar Geometry IQ?

Test your knowledge by taking the solar geometry quiz!


PV  (photovoltaics)  (highest cost)

Passive solar (low cost)


Ventilation preheating

Active solar

Shading (moderate cost)

Window size (free?)

Window placement (free)

Building color (free)

Building orientation (free)

Tree of Solar Strategies


Solar has become almost synonymous with solar cells (PV), which is unfortunate because PV is the high hanging fruit and it makes sense to pick the low hanging fruit first.  The free and easy strategies should be used before the expensive and difficult ones.


For schools of architecture:  The best heliodons for teaching and understanding solar geometry and solar strategies are the conceptually clear Sun Simulator and Sun Emulator.  However, if space and or money are in short supply, it is better to have a less than ideal heliodon than none-at-all.   In that case, the combination of the Table-top and Solar Geometry Demonstration Heliodon is a good choice.  The Solar Geometry Demonstration Heliodon can be used to teach solar geometry and solar strategies while the Table-top heliodon can be used to further teach strategies and to very accurately test models either indoors with a light or outdoors using the sun.


For Energy Centers or Science Museums:  The Sun emulator is ideal for non-academic applications because it can explain solar geometry for the whole planet, and because it can demonstrate solar strategies as related to solar geometry.  However, the Sun Emulator is too delicate to be left out without supervision.  The rugged Sun Simulator is ideal as an unsupervised exhibit that is very easy to use because it simulates the sun’s movement across the sky at a particular latitude, and it is sturdy and the only moving parts are switches.

Other Heliodons

Although many other types of heliodons have been developed over the years, most are not included on this website because they are not recommended, they are not commercially available, or there are no drawings available.  Any heliodons that are recommended and are either commercially available or their construction drawings are available are found on the “Other Heliodons” page.

Norbert Lechner Heliodon Presentation


Norbert Lechner demonstrating his Heliodon at University of Nebraska at Omaha.


This is a video of a lecture called "Daylighting is Mostly Sunlighting" that Prof. Lechner gave at the University of Nebraska at Omaha.  The first half of the video consists of a slide presentation and the second half of a heliodon demonstration.





Heliodon Presentation by Norbert Lechner


Filmed by Blue Collar Builders @ INTER SOLAR 2014 / SemiCon West 2014 - Heliodons


Watch now...


Heliodon demonstration in Atlanta, Georgia


http://www.sawhorse.net Matt Hoots interviews Prof Lechner at Greenprints 2011. Prof. Lechner demonstrates how a heliodon can help demonstrate how to build a green home.







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