thumb|Heliodon of Analemas

thumb|A Heliodon Animation

A heliodon (HEE-leo-don) is a device for adjusting the angle between a flat surface and a beam of light to match the angle between a horizontal plane at a specific latitude and the solar beam. Heliodons are used primarily by architects and students of architecture. By placing a model building on the heliodon’s flat surface and making adjustments to the light/surface angle, the investigator can see how the building would look in the three-dimensional solar beam at various dates and times of day.

History

Shortly after World War II, in the 1950s, there was a wide interest in producing building design techniques that correspond to the climate. At Princeton Architectural Laboratory, Thermoheliodon was invented by Olgyays in hopes to create physiological conditions of human comfort through architectural design. Thermoheliodon was a domed insulated evaluation bed for scaled architectural models in certain climatic conditions measured to a high level of calculation and accuracy. The institution aimed to enhance housing conditions and development of local resources for construction in colonial territories. This heliodon consists of a platform created to hold a model of the building whose isolation is to be evaluated. This heliodon is combined with a sky scanning simulator (artificial sky) to predict the light distribution in a building over the entire year. He invented heliodons which were much easier to evaluate daylight simulation than the previous models. The architect designed the Orchard Heliodon with similar features to the Sun Emulator heliodon (developed by Norbert Lechner). For more precise simulations, Orange Heliodon, an easy-to-use robotic heliodon with a fixed light source was designed and was launched in the market in 2007. It used a computerized and automatic heliodon to reproduce the sunshade. Moreover, a tabletop heliodon with a moving light source was developed for architect offices. A patented portable direct sunlight light-duty universal heliodon set up on a camera tripod was developed for evaluating the impacts of direct sunlight on small architectural models or building components.

Scientific background

The Earth is a ball in space perpetually intercepting a cylinder of parallel energy rays from the Sun. (Think of a tennis ball being held in the wind.) The angle of any site of Earth to the solar beam is determined by

  • The site’s latitude, which gives its position on the curve of the Earth between the Equator and one of the Poles.
  • The time of day at the site, measured by its progress eastward around the Earth’s axis from sunrise to sunset.
  • The date, which locates the Earth on its annual orbit of the Sun.

The change due to date is the most difficult to visualize. The Earth’s axis is steady but tilted: the plane that includes the Earth’s equator, which is perpendicular to the axis, is not parallel to the plane that includes the center of the Sun and the center of the Earth, called the ecliptic. Think of the Earth as a car on a Ferris wheel. The car’s axis always points “down”, which changes its relation to the center of the wheel. A light at the center of the wheel would touch the bottom of the car at the top of the orbit and the top of the car at the bottom of the orbit. As the Earth orbits, the location of the centerline of the solar cylinder changes, sliding from the Tropic of Cancer (in June) to the Tropic of Capricorn (in December) and back again. This changes sun angles all over Earth according to the date. See more at analemma.

Utility

Heliodons can mimic latitude, time of day, and date. They must also show a clear north-south direction on their surface in order to orient models. Some heliodons are very elaborate, using tracks in a high ceiling to carry a light across a large studio. Others are very simple, using a sundial as a guide to the adjustments and the sun of the day as a light source. In general, the date adjustment causes the most difficulty for the heliodon designer, while the light source presents the most problems in use. The parallel rays of the sun are not easy to duplicate with an artificial light at a useful scale, while the real sun is no respecter of deadlines or class hours.

All heliodons can benefit by including a moveable, tiltable device that can be set to match any surface on a model to show angle of incidence. The angle of incidence device indicates the relative intensity of the direct beam on the surface. The device consists of a diagram of concentric rings around a shadow-casting pointer perpendicular to the diagram. Each ring represents a percent of the direct solar beam incident on the surface. The percentage varies from 100%—the ray runs straight down the pointer perpendicular to the diagram—to zero—the ray runs parallel to the diagram and misses surface. The cosine of the angle of incidence gives the percentage. A cosine of 0.9, 90%, for example, corresponds to an angle of incidence of 26.84 degrees. The radius of the ring for the angle is equal to its tangent times the height of the shadow casting pointer. A 45 degree angle of incidence would generate a cosine of about .7, 70%, for example. Since the tangent of 45 degrees is 1, the radius of the 70% ring would be equal to the height of the shadow-casting rod.

Types of Heliodon

Manual Tabletop Heliodon

Manual Tabletop heliodons are used for sun shading analysis at any given latitude and at any time. The model support platform is mounted on a conventional table or desk. It can rotate and tilt a scaled architectural model. These heliodons are manually operated without the use of computers and provide good accuracy. The model stand, mounted on the table, is tilted for latitude and rotated to get the time of the day. This heliodon requires only limited training since it is easy to understand and operate.

Considering the characteristics, the manual sun emulator is also excellent for explaining solar dynamics and cardinal points to children in a function, scientific and fun way of demonstration.

Manual sun emulator heliodon is used in various universities such as:

  • Auburn University, Alabama -  The university uses a 48” (1.2 m) diameter Formica covered sun emulator heliodon known as HPD Model 126 Heliodon.
  • Southeastern Louisiana University, Louisiana – The university uses heliodon as an interactive tool for teaching purposes in designing solar aware architecture.
  • Durham School of Engineering and Construction, Nebraska – Prof. Norbert Lechner uses sun emulator heliodon to explain sun shading analysis of scale model.
  • CERES Center at Ball State University, Indiana The robotic heliodon is used for evaluating solar paths and their interaction with pre-existing or new constructions. The lighting simulation from the heliodon helps in quickly identifying the daylight penetration on the buildings. Arup uses the robotic heliodon to design sustainable, energy-efficient, and award-winning concepts in lighting.

Robotic Heliodon with Fixed Model

This robotic heliodon is fully automated with a computer and has lights that go around the fixed scale model placed horizontally on the table. This kind of robotic heliodon is used separately or integrated with dome artificial sky for presentation, lighting design and research purposes. While in use with the artificial sky, the combined tool can replicate both the Sun and the sky for great accuracy and obtain results of the daylight study. The fixed scale model can be bigger and heavier models than the other types which allow the source to go around the model for obtaining evaluation results, conducting presentations and observation. The robotic heliodon allows people to move easily around and inside it for daylighting studies.

thumb|Daylight Planning Lab - Stuttgart Technology University of Applied Sciences (HFT Stuttgart)

The automated robotic heliodon with a fixed model is used in research facilities, lighting companies and university laboratories such as:

  • University of Kansas Lighting Research Lab, Lawrence, United States uses a heliodon sunlight simulator for daylight studies and research purposes. The device was developed by Dr Hongyi Cai and custom-made in China by Quanzhou HuaTian Measurement Equipment LLC. The lab uses two elements in their daylight simulator – an artificial sky and artificial sun. The lighting firm uses heliodon for daylight simulation in research and development for complex building structures. The heliodon is powered by a 1200W HMI lamp with a custom-designed optical setup able to reproduce a range of 200,000 lx to 600,000 lx on the table supporting the scale model. The handbook is a globally well-known reference and a guide to allow lighting professionals and practitioners to understand the impact of light on human health and promote sustainability through efficient lighting study and design.