What Is Lighting?

Lighting is the deliberate application of artificial or natural light to illuminate spaces, surfaces, and objects for functional, safety, or aesthetic purposes. As a field of engineering and applied science, lighting encompasses the design, specification, and evaluation of light sources, luminaires, control systems, and the optical and electrical infrastructure that supports them. It draws on physics, electrical engineering, and human factors research, and is governed by standards from bodies including the Illuminating Engineering Society (IES) and the IEEE Industry Applications Society.

The technical goals of a lighting system extend beyond simple visibility. Engineers account for illuminance levels, luminous efficacy, color rendering, glare control, and the interaction between artificial light and human circadian physiology. These requirements vary substantially between residential, commercial, industrial, healthcare, and outdoor environments.

Lamp Technologies

The evolution of light sources from incandescent to solid-state has been the defining development in modern lighting engineering. Filament lamps, including incandescent and tungsten-halogen types, produce light by resistively heating a tungsten wire until it emits thermal radiation. They deliver excellent color rendering but low luminous efficacy, typically 10 to 20 lumens per watt. Fluorescent lamps improved efficacy substantially by exciting mercury vapor to produce ultraviolet radiation that a phosphor coating converts to visible light; linear fluorescent tubes and compact fluorescent lamps achieve 50 to 100 lumens per watt. Light-emitting diodes (LEDs) now dominate new installations, offering efficacies above 150 lumens per watt in commercial products, operational lifetimes measured in tens of thousands of hours, and the ability to produce tunable color temperatures. The IEEE 3001.9 standard, developed jointly with the IES as IEEE/IES Recommended Practice for the Design of Power Systems Supplying Lighting Systems, provides power-system design guidance for these varied source types in commercial and industrial settings.

Photometry and Measurement

Photometry is the branch of radiometry concerned with the measurement of light as perceived by the human visual system. Its quantities are weighted by the luminous efficiency function, which peaks near 555 nm for photopic (daytime) vision. Key photometric quantities include luminous flux (lumens), illuminance (lux, or lumens per square meter), luminance (candelas per square meter), and color rendering index (CRI). CRI describes how faithfully a source renders object colors relative to a reference illuminant; a CRI of 100 indicates a perfect match. Correlated color temperature (CCT) describes whether a source appears warm or cool, measured in kelvins, with residential applications typically favoring 2700–3000 K and office environments preferring 3500–5000 K. Measurement protocols for these quantities are standardized by the CIE and adopted in IEEE and IES publications, including methods for solid-state lighting measurement.

Lighting System Design

A lighting design integrates the choice of light source with luminaire selection, room geometry, surface reflectances, and control strategy to achieve target illuminance levels. Design calculations use point-by-point photometric methods or the zonal cavity method to predict average maintained illuminance across a workspace. The maintained illuminance accounts for lumen depreciation over the lifetime of the source and the accumulation of dirt on luminaires and room surfaces, captured through a light loss factor. Daylighting integration, where glazing and shading systems supplement or replace artificial lighting during daytime hours, can substantially reduce energy consumption. Energy use data from the U.S. Energy Information Administration shows that commercial buildings using advanced lighting controls and high-efficacy sources achieve significant reductions in lighting energy intensity compared to earlier construction.

Applications

Lighting has applications in a wide range of fields, including:

• Commercial buildings, where energy codes mandate efficacy and control requirements
• Industrial facilities requiring task-specific illuminance for safety and productivity
• Roadway and area lighting for pedestrian and vehicle safety
• Healthcare environments demanding precise color rendering and infection-control compatibility
• Horticultural and plant growth lighting tuned to photosynthetically active radiation