Design Considerations
Last Update: November 1, 2010
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Validation — Lighting Analysis Tools

Lighting calculations have always been part of the basic practice of illuminating engineering. Calculations using a simple hand calculator (or slide rule) were once common, but the results of this type of calculation are limited to broad generalizations and averages. These days, computer calculations, requiring merely a modest personal computer and relatively low-cost software, are the standard for virtually every lighting practitioner.

This section describes tools and methods for making lighting calculations (see Lighting Analysis Tools following) and evaluating the cost effectiveness of design alternatives.

Hand Calculations
Hand calculations are useful when you need a quick go/no go for a particular luminaire & lamp selection, when the room analyzed is a fairly standard shape with typical surface characteristics, or you want to “work backwards” from a target illuminance level to determine desired parameters.
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Computer Programs
These programs determine light levels at specific locations in a space. They can predict the brightness of room surfaces and give the patterns of light on the ceiling, walls and floor. Some programs calculate special figures of merit such as metrics of lighting quality and visual performance.
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Specialty Calculations
There are several lighting calculations that are best performed using a program specifically designed for them.
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Exterior Calculations
Exterior lighting programs are used for parking lots, roadways, pedestrian paths, and special situations such as airport aprons, car sales lots and sports fields. Exterior lighting calculations are very similar to interior calculations, except that they are simpler, since no light reflectance from room surfaces are calculated.
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Daylighting Analysis Tools
Unlike electric luminaires, daylight apertures are not routinely tested for their photometric performance. This is beginning to change due to the renewed importance in calculating the daylighting component of the lighting system.
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Calculation Software
Many architectural spaces are more geometrically complex than is readily handled via manual calculations. A wide variety of software design packages have been developed to assist the designer in verifying and altering the design.
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Energy Simulation Programs
Energy simulation programs such as DOE-2, BLAST and EnergyPlus are not really lighting programs, but they do simulate the energy used by lighting systems and are useful in evaluating the interactions between lighting system improvements and HVAC systems.
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Application Guidelines
Lighting design strategy often determines the appropriate type of lighting calculation. Two design approaches are discussed here: general lighting approaches and task-ambient lighting approaches.
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