Light distribution is a function both of the lamp and the fitting, since in most cases the fitting controls the direction and the power of the light source. The designer needs to understand the distribution pattern of a particular fitting and this is best achieved by looking at a diagram called a polar curve for the fitting in question. This plots the outline and intensity of light from a specific fitting.
The intensity of light falling on a particular surface, for example a workshop, sales point, or display is translated by looking at the incident light falling on it in lumens. There are guidelines available for the desired level of lighting in different work and retail situations; in some case these are linked to official regulations, and the designer needs to be aware of these.
Some recommended levels of lighting are as follows: the recommended level of illuminance in lux (one lumen per square meter) for small shops is 500 lux, for supermarkets and hypermarkets it is the same amount, calculated on vertical faces of displays, and for checkout areas also 500 lux calculated on the horizontal plane of the checkout or sales area. These can be compared with levels of 150 lux, deemed appropriate for areas such as loading bays, 750 lux for drawing offices, and 1,500 lux for hand tailoring, operating theatres and suchlike.
The diffusion of light refers to the overall level of lighting achieved in a scheme by the complete installation. Computer programs are now widely available for calculating these results, and for testing alternative solutions for a specific interior space.
To calculate lighting values exactly, lamp and lighting manufacturers have created programs that will produce an outline of lighting levels in a regular space from exact technical data. These programs allow the architect or designer to check that lighting distribution and levels meet, for example, health and safety requirements. However, such programs do not produce a rendered image, so that the visualization process is incomplete. High-end graphics programs can create visually appealing images, either from CAD data or from the designer’s eye and technical programs can describe the lighting solutions exactly. What remained to be done was to marry the two up so that the designer could show a client an accurate view of the project.
Two recent programs have squared this particular circle. The first, Lightscape, is a stand-alone program. It offers a series of libraries of surfaces, elements and light fittings that can be assembled to replicate an interior and can then be lit. The complete radiosity program calculates the lighting effect accurately and from all positions. Lightscape are also regularly releasing further libraries that contain both architectural elements and specific light fittings to extend and enhance the range of luminaires that can be used under lightscape.
Radioray, developed for Autodesk by the UK Company LightWorks, is a plug-in for 3DStudioMax and 3DStudioViz. This also allows precise light fittings to be inserted into interiors created in 3DStudio, using the industry standard elx file extension. These files, created by lamp and fitting manufacturers, contain complete photogrammetric data allowing the exact performance of a lamp and fitting to be depicted. So in a finalized and rendered design, precise lux values can be read off walls and work surfaces, and the colour and diffusion of light are also visually accurate. Again, since this is a radiosity program, the values are created for all viewpoints.
