^ The symbols in this column denote dimensions ' L', ' T' and ' J' are for length, time and luminous intensity respectively, not the symbols for the units litre, tesla and joule.

Luminous efficacy normalized by the maximum possible efficacy Luminous efficiency, luminous coefficient Ratio of luminous flux to power consumption The candela per square metre is sometimes called the nit. Luminous flux per unit solid angle per unit projected source area. The lumen second is sometimes called the talbot. Luminous intensity of artificial light sources is typically measured using and a goniophotometer outfitted with a photometer or a spectroradiometer. The curve which represents the response of the human eye to light is a defined standard function y(λ) or V(λ) established by the International Commission on Illumination (CIE, for Commission Internationale de l'Éclairage) and standardized in collaboration with the ISO. Light with the same radiant intensity at other wavelengths has a lower luminous intensity. When adapted for bright conditions ( photopic vision), the eye is most sensitive to yellow-green light at 555 nm. The human eye can only see light in the visible spectrum and has different sensitivities to light of different wavelengths within the spectrum. Photometry deals with the measurement of visible light as perceived by human eyes. The SI unit of luminous intensity is the candela (cd), an SI base unit.

^ Born & Wolf 1999, p. 448, Section 8.6.In photometry, luminous intensity is a measure of the wavelength-weighted power emitted by a light source in a particular direction per unit solid angle, based on the luminosity function, a standardized model of the sensitivity of the human eye.

^ 'Fresnel and Fraunhofer Approximations'.

^ 'Fraunhofer, Joseph von (1787-1826) - from Eric Weisstein's World of Scientific Biography'.As the spread of wavelengths is increased, the number of 'fringes' which can be observed is reduced.

If the spread of wavelengths is significantly smaller than the mean wavelength, the individual patterns will vary very little in size, and so the basic diffraction will still appear with slightly reduced contrast. it consists of a range of different wavelengths, each wavelength is diffracted into a pattern of a slightly different size to its neighbours. In all of the above examples of Fraunhofer diffraction, the effect of increasing the wavelength of the illuminating light is to reduce the size of the diffraction structure, and conversely, when the wavelength is reduced, the size of the pattern increases. If the aperture is in x ′y ′ plane, with the origin in the aperture and is illuminated by a monochromatic wave, of wavelength λ, wavenumber k with complex amplitude A( x ′, y ′), and the diffracted wave is observed in the unprimed x,y-plane along the positive z Non-monochromatic illumination In Cartesian coordinates Diffraction geometry, showing aperture (or diffracting object) plane and image plane, with coordinate system. The Fraunhofer diffraction equation is an approximation which can be applied when the diffracted wave is observed in the far field, and also when a lens is used to focus the diffracted light in many instances, a simple analytical solution is available to the Fraunhofer equation – several of these are derived below. The Kirchhoff diffraction equation provides an expression, derived from the wave equation, which describes the wave diffracted by an aperture analytical solutions to this equation are not available for most configurations. When a beam of light is partly blocked by an obstacle, some of the light is scattered around the object, and light and dark bands are often seen at the edge of the shadow – this effect is known as diffraction.

Equation for intensity fo light