Are lighting application software programs useful for people who are not involved in lighting design full time?

Lighting application software programs are not as intimidating as they once were. Depending on the type of program, they are user friendly for novices as well as full time lighting designers. But, this ease of use is like a double-edged sword: if you don't know the fundamentals, you can wind up with a less than desirable lighting system.

With this in mind, let's see what's currently available from lamp and lighting fixture manufacturers.

Software program categories

Engineers and contractors are using lighting software programs to assist in the design of new construction projects and in planning the retrofit of existing facilities. These programs are generally classified into two categories.

* Less powerful retrofit/relighting programs, which may have some lighting design capability.

* More powerful programs, which can prepare a complete lighting design layout and fixture schedule while also creating graphic representations of a project.

Less powerful programs. Used for both interior and exterior projects, the less expensive (or free) software programs offered by the major lamp manufactures use a relatively simple and straight forward calculation called the zonal cavity method. You simply insert numbers into one or more formulas, and the required calculations are made, allowing you to determine an economic course of action. The zonal cavity method is ideal for rapid calculations, when fast comparisons are desired. The software is easy to use, since most employ the point-and-dick method of going through the steps.

A typical less powerful program can do the following.

* Compare different lamp types or lighting systems to determine the most cost effective choice based on total lamp, power, and labor costs against the quantity of light delivered.

* Plan the most effective lighting system maintenance schedule and provide productivity analysis, demand charges, and environmental impact factors, which can be printed out for presentation.

More powerful programs. The more powerful (and expensive) programs sold by independent software firms use the point-by-point method of calculation, which is very accurate and precise and which can also be used for graphic renderings. These programs run best on a microcomputer (a PC) with a 486DX2 microprocessor, which has a math co-processor. This is needed to handle the large amount of computation required in doing point-by-point calculations. The less expensive 486SX chip does not have a math co-processor.

Today, the cost of a well-equipped, 486 chip-based PC with the necessary graphics card, color monitor, graphic user interface (the mouse), etc., is about $2000. So, if you might have a once- or twice-a-month application need for a lighting design program, you would find one of the more powerful software packages to be an economical investment.

One development that's spurring the use of these software programs is the availability of photometric data files: These files are in the Illuminating Engineering Society (IES) standard format, so that files of fixture products from just about any manufacturer can be put into the data base.

Fixture manufacturer programs

Some lighting fixture manufacturers also offer sophisticated lighting design programs. In general, these programs can cost from $300 to more than $800.

One popular indoor/outdoor lighting design and analysis program provides calculations for all lighting metrics, including illuminance, exitance, surface luminance, point-by-point horizontal and vertical illuminance, room surface luminance, visual comfort probability (VCP), and relative visual performance (RVP). With this program, you can enter data graphically and even extract the data from an AutoCAD DXF file. An integral photometric file editor allows you to create standard format IES and TM14 (used in the United Kingdom) photometric data files in just minutes. Output from the program can be viewed as contour plots, and gray-scale renderings can be produced for any viewing position within the space.

Another indoor/outdoor lighting design and analysis program uses simple, largely intuitive commands; a tutorial makes it easy to learn the features. With this program, you have the option of using either a digitizer tablet or a mouse. The software is particularly useful for special applications such as parking lots, tennis courts, and other outdoor sports facilities and building sites. Although not a full-fledged CAD program, it has the essential tools to create a background drawing for lighting design and calculations. The program also can import CAD drawings in DXF file formats and allows the change of colors for minimum and maximum light levels. Also included is an extensive symbols library, which approximates the new IES Symbols Design Guide.


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Illuminance: The density of light falling on a surface. Its unit is called the footcandle when using the English measurement system and lux when using the international system.

Point-by-point method: A design procedure for determining the illuminance at various locations in a lighting system using luminaire photometric data. The direct component of illuminance from the luminaire(s) and the inter-reflected components of illumination for the room surface would be calculated separately.

Radiant exitance: The density of radiant flux leaving a surface. It is expressed in watts per unit area of the surface.

Visual comfort probability (VCP): The rating of a lighting system expressed as a percentage of people who, when viewing from a specific location in a specific direction, will be expected to find the installation acceptable in terms of discomfort glare.

Relative visual performance (RVP): The quantitative assessment of performance of a visual task, taking into account speed and accuracy.

Zonal cavity method: A method of calculating average illumination levels that assumes each room or area is divided into three cavities. These include the ceiling cavity (extending from the lighting fixture plane to the ceiling), the room cavity (the space between the fixture plane and the work plane), and the floor cavity (the space extending from the work plane to the floor). If the lighting fixtures are recessed, there is no ceiling cavity; likewise, if the work plane is at floor level, there is no floor cavity. By treating each of these spaces separately, the effect of the differences in reflectance values of the ceiling, walls, and floor can be determined, as well as the inter-reflection of light among the various room surfaces.