Lighting lexicon for the LUMIMAX® knowledge base: technical terms relating to lighting and Machine Vision
Some of the technical terms used in our knowledge series are explained in alphabetical order below.
Bandwidth
The bandwidth refers to the wavelength range that is transmitted by a filter.
Bandpass filter
A bandpass filter transmits a specific wavelength range. The remaining light is blocked. The width of this transmission band is selected depending on the intended use. There are filters with a bandwidth of less than 2nm up to bandwidths of 80nm and more. Very narrow-band filters with a width of 2 to 5 nm are mainly used for demanding laser applications. Filters with a bandwidth of 10 to 80nm can in turn be used for various applications in image processing.
Black body radiator
A black body (also: black body radiator, Planckian radiator, ideal black body) is an idealised thermal radiation source. The idealisation is that such a body completely absorbs all incident electromagnetic radiation of any wavelength. At the same time, it emits thermal radiation whose intensity and spectral distribution are independent of the nature of the body and its surface and depend only on its temperature. Its thermal radiation is stronger than that of any real body of the same temperature with the same surface area in every wavelength range. Such bodies serve as a basis for theoretical considerations and as a reference for practical investigations of electromagnetic radiation. (Source: www.wikipedia.de, 2025)
Block area
The blocking range describes the wavelength range that is blocked by the filter.
Brewster’s angle
Brewster’s angle – also ‘polarisation angle’ – considers an unpolarised light source and describes the angle at which only the polarised portions of this light perpendicular to the incident plane are reflected. According to this law, if unpolarised light falls onto the surface at the right angle, it will be reflected back from the surface as a beam of linearly polarised light.
Bright field
Bright field illumination is a form of incident light illumination. If the lighting is aligned so that the light is reflected directly back into the camera, this is referred to as a bright field arrangement.
Centre wavelength (CWL)
The centre wavelength indicates the midpoint of the two wavelengths at which 50% of the maximum transmission is achieved.
Cloudy day lighting
See Dome lighting
Coaxial mirrored illumination
With coaxial mirrored illumination, diffuse, homogeneous illumination is introduced directly into the beam path of the optics via a semi-transparent mirror. As a result, the object is illuminated very homogeneously and without shadows. The vertically incident light is reflected from the flat surface directly back into the camera.
Dark-field illumination
Dark-field illumination is when the illumination is arranged in such a way that the light reflected from the test object surface is reflected away from the camera. For this reason, the object appears dark in the image. If the light hits an unevenness, the light rays are deflected. As a result, defects, contours and edges appear bright in the image. Dark field illumination can be arranged both in incident light and transmitted light.
Dome lighting
Dome lighting, also known as shadow-free lighting or cloudy day lighting, is a special form of incident lighting. Diffuse light is directed onto the test object from all directions using a dome-shaped reflector. This creates a completely shadow-free illumination.
Illuminance level
Illuminance describes the luminous flux (lumens per square metre) that is incident on a surface from a lighting system. Illuminance corresponds to one lux when one square metre of surface is illuminated with a luminous flux of one lumen. You can therefore convert 1 lumen / square metre into 1 lux. But beware: when measuring illuminance, the V-lambda curve is used as a weighting. This means that green light has a higher lux value than blue or red light with the same light energy. Illuminance is therefore a visual, photometric measurement.
Incident light
Lighting that is arranged from the direction of the camera and therefore above the object plane.
Irradiance
This describes the sum total of electromagnetic energy or optical radiation energy that falls as light onto the surface. The value is given in watts per square metre. From this particular perspective, the sensitivity of the human eye is not considered at all.
Lambertian scatterer
A Lambertian scatterer is an emitter for which the radiance over the entire light field is constant in all directions.
Law of reflection
Angle of incidence of the light beam = angle of reflection of the light beam
Lighting angle
Angle at which the illumination is arranged in relation to the object plane and the camera. Depending on the arrangement, a distinction is made between bright field, partial bright field and dark field illumination.
Lighting geometry
The lighting geometry describes the form of the lighting, e.g. area lighting, ring lighting, spot lighting.
Luminescence
Luminescence is the optical radiation produced during the transition from an excited state to the ground state. A distinction is made between two forms of luminescence: phosphorescence and fluorescence.
Phosphorescence
Phosphorescence describes a similar effect to fluorescence, but in this form the material glows after the end of the irradiation. The afterglow can last up to several hours, but can also fade after fractions of a second. The duration depends on the phosphorescent material and the irradiance.
Polarisation
Polarisation describes the process by which light is limited to a single direction of oscillation.
Polarising filter
A polarising filter in front of the lighting only transmits one direction of light oscillation. All beams with other directions of oscillation are not transmitted.