The IES defines illumination engineering terms in ANSI/IES LS-1-22, is available here online. You can search terms by their first letter using the categories listed in the Categories window, by the first letter of the term in the alphabetical list below, or by typing the term in the search window. You can find the Introduction material for LS-1-22 on these pages:
Copyright, Disclaimer, and American National Standards Statement
Foreword, Nomenclature Committee members, Introduction, and Scope

- phototherapy
- phototropism
- physical photometer
- physical receptor
- pigtail
- pilot house control
- pin plug or connector
- pipe
- Planck radiation law
- Planckian locus
- plano-convex spotlight
- plate
- plot
- point brilliance, E
- point-by-point method
- point method
- point of fixation
- point of observation
- point source
- point vision
- polarization
- polarized radiation
- pole
- portable lighting
- portable luminaire
- portable traffic control light
- position index, P
- position lights
- practical lamp (television, film and theater)
- pre-burning time
- prefocus lamp
- preheat (switch start) fluorescent lamp
- preset
- pressed reflector lamp
- primary color
- primary line of sight
- primary standard
- profile angle
- profile spotlight
- projection lamp
- projector
- protective lighting
- proximal stimulus
- psychometric chroma
- psychometric hue-angle
- psychometric lightness
- psychometric saturation
- public way
- pulsed lamp
- pupil (pupillary aperture)
- Purkinje phenomenon
- purple boundary
- quality of lighting
- quantity of light (luminous energy, Q)
- quartz lights
- quartz (or quartz iodine, or quartz halogen)
- quick-flashing light
- radiance
- radiant efficiency
- radiant energy density
- radiant energy, Q
- radiant exitance
- radiant exposure
- radiant exposure rate
- radiant fluence
- radiant fluence rate
- radiant flux areal density
- radiant flux density at a surface
- radiant flux maintenance
- radiant flux (radiant power)
- radiant intensity
- radiant sterisent
- radiator
- radiometry
- radiosity
- rail lights
- range lights
- rapid-start fluorescent lamp
- rated lamp life
- ray tracing
- Rayleigh scatter
- reaction time
- rear screen projector
- reciprocal color temperature
- reciprocity
- recoverable light loss factor
- redirecting surfaces and media
- reference ballast
- reference line
- reference standard
- reflectance factor, R
- reflectance, ρ (of a surface or medium)
- reflected direct luminaire
- reflected glare
- reflected radiation coefficient, RRC
- reflection
- reflectivity
- reflectometer
- reflector
- reflector lamp