The architecture of light: architectural lighting design concepts and techniques. A textbook of procedures and practices for the architect, interior designer and lighting designer pdfdrive com

Chapter 20 Lighting Calculations

It is imperative before delving into the world of lighting calculations to step back and remember the reason for using calculations in design. We use calculations to help us arrive at specific solutions to critical lighting challenges. If a calculation will help us select a luminaire, and apply that luminaire to create the lighting effect we are after, we welcome it. It is important not to rely on calculations too heavily as they are merely a supplement to good lighting instinct and experiential knowledge. It is also important not to assume that every lighting element we are designing can benefit from performing a calculation.
Lighting calculations can assist us in selecting lamps and luminaires when
we are trying to obtain a specific light level. Lighting calculations also help us predict the lighting effect we may get from a specific lighting scenario.
We will investigate two lighting calculation methods that help us in two
types of lighting situations: Lumen Method Calculations and Point Calculations.
Lumen Method calculations are used for determining average light levels in large, open areas.
Point Calculations are used for determining light levels at a specific point on an object or surface.
These two calculations cover the two ends of the design spectrum: broad, spatial light levels and minute, point-specific light levels.
To understand how we make use of lighting calculations, we must first
investigate more specifically the way we count and measure light.
In the case of both types of calculations, we will be using Illuminance as our measurement of light level. Illuminance is, of course, the measure of light falling onto surfaces. Specifically, illuminance is the measure of the number of lumens that are falling onto a square foot of area, which is the definition of a foot-candle, the unit of measurement of illuminance. A foot-candle is one lumen of light received evenly over an area of 1 square foot.