This article will provide a basic overview on how to read a photometric diagram and interpret it into a useful information. So, what exactly a photometric diagram stands for? It is a visual representation of a light diffused by a lighting fixture, which provides a valuable information on how the light is distributed and falls upon a surface. In other words, the diagram shows what kind of light distribution is expected from the lighting fixture.
Interpretation of the photometric diagram
In order to better understand the logic behind the photometric diagram, let’s review diagram of Hydra lighting fixture as an example.
The middle of the diagram shows the position of the lighting fixture. In turn, the lines coming from the centre indicate angles of the light distribution, while circles describe the light intensity. In this way the diagram makes it easy to deduce the light intensity (measured in Candela) in different angles. For example, the point A shows that the intensity of light at 30° will be 250 Candela.
Additionally, the diagram provides an important information by showing the amount of light distributed in both directions (upwards and downwards). The part of the graph which is located above the horizontal line 90° shows the amount of light distributed upwards. In turn, the part before the line indicates the amount of light distributed downloads.
C0-C180 indicate the front view, while C90 – C270 refers to the side view. The shape of these both lines are about the same in most of the cases, especially when it comes to down lights.
Below, there are examples of photometric diagrams of various lighting fixtures.
Recessed light - Iiris
Spot light - Spike
Bollard light - Lacuna Plaza
All in all, the photometric diagram is in an essential component while creating a lighting plan as it enables the designer to choose the suitable lighting for the application, which will enable the proper illumination in the space.
Photometric Data Files
Information about a lighting fixture photometrics is also available in a file format for the building information modeling softwares such as Autodesk Revit. There are various files types which can be used for this purpose, but one of the most common is IES files. IES is a commonly used file type which provides the information about the light distribution of a lighting fixture. These files include information about light quantities, measurements as well as result in more accurate and realistic rendered images, that is why they are very useful when it comes to 3D design. Each fixture would use the IES data to accurately show how the lighting fixtures would appear in the application, be it an industrial, office or residual space.
In order to make it easier for designers to create a lighting design, Winled IT department together with BIM specialists designed LIGHTS plugin for Autodesk Revit. LIGHTS is a comprehensive LED luminaire library with over 70 families. All the lighting fixtures in the LIGHTS feature photometric data files, which makes the lighting design more realistic.