The IEC 62471 series gives guidance for evaluating the photobiological safety of lamps and lamp systems including luminaires. The IEC 60825 series gives guidance on safety relating to exposure of the eye to lasers, which are high luminance sources. Photochemical effects can also cause damage, especially at short wavelengths. Damage can occur because of local heating of the retina. Retinal damage can occur when the eye is exposed to high luminance. The image can never be "brighter" than the source. The light at the image plane, however, fills a larger solid angle so the luminance comes out to be the same assuming there is no loss at the lens. As an example, if one uses a lens to form an image that is smaller than the source object, the luminous power is concentrated into a smaller area, meaning that the illuminance is higher at the image. This means that for an ideal optical system, the luminance at the output is the same as the input luminance.įor real, passive optical systems, the output luminance is at most equal to the input. Luminance is invariant in geometric optics. The sun has a luminance of about 1.6 ×10 9 cd/m 2 at noon. A typical computer display emits between 50 and 300 cd/m 2. Luminance is used in the video industry to characterize the brightness of displays. In this case, the solid angle of interest is the solid angle subtended by the eye's pupil. Luminance is thus an indicator of how bright the surface will appear. Luminance levels indicate how much luminous power could be detected by the human eye looking at a particular surface from a particular angle of view. Luminance is often used to characterize emission or reflection from flat, diffuse surfaces. The unit in the Centimetre–gram–second system of units (CGS) (which predated the SI system) is the stilb, which is equal to one candela per square centimetre or 10 kcd/m 2. A non-SI term for the same unit is the nit. The SI unit for luminance is candela per square metre (cd/m 2). īrightness is the term for the subjective impression of the objective luminance measurement standard (see Objectivity (science) § Objectivity in measurement for the importance of this contrast). The procedure for conversion from spectral radiance to luminance is standardized by the CIE and ISO. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls within a given solid angle. Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. JSTOR ( April 2023) ( Learn how and when to remove this template message)Ī tea light-type candle, imaged with a luminance camera false colors indicate luminance levels per the bar on the right (cd/m 2).Unsourced material may be challenged and removed. Please help improve this article by adding citations to reliable sources. This article needs additional citations for verification.
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