How is luminance measured?

It offers new difficulties for luminance measurement , especially in developing new sources and new lighting technologies. LISUN has therefore created several goniophotometers using different test techniques for luminance measurement.

It is a photographic measure of luminous intensity in a particular order per unit area of ​​​​light. It represents the quantity of light going through, emitted, or reflected from a specific region and falls inside a specific solid angle. It shows how vivid we see the outcome of the light and surface interactions.

Why is luminance used?
Luminance is frequently used to describe flat diffuse surfaces emission or reflection. Luminance levels show how much luminous power a human eye can perceive from a given viewpoint on a particular surface. The light is, therefore, an indication of the brightness of the surface. In this instance, the solid angle of interest is the solid angle subdued by the pupil of the eye.

Luminance is used for characterizing the brightness of screens in the video business. In geometric optics, luminance is invariant. This implies that the brightness at the output is the same as the input luminance for the perfect optical system.

The output brightness for genuine, passive optical systems is at most equal to the input. For example, if you are using a lens to create an image that is smaller than the source item, the light energy is focused in a smaller region, which means that the illumination of the image is more excellent. However, the light at the picture plane covers a wider solid angle such that the brightness is the same if no lens loss is seen. The picture cannot be “brighter” than the source.

Luminance measurement
For luminance measurement, the following devices are in use.

Luminance meter
A photometric light meter is a device that can measure the brightness in a particular direction with a specific solid angle. The simplest devices measure the light in one order, while pictures measure brightness to how a digital camera captures color photos.

You can use the luminance meter to test any light source’s brightness: bulbs, lighting systems, indications on the roadside, LEDs, LCDs, etc. In addition to conventional light meters, colorimeter versions are intended to measure the color and intensity of the light source (RGB).

Goniophotometer
Spectrophotometry is the goniophotometer technique for the testing of total luminance. The idea is to check light intensity in various directions (or the illumination at a certain distance from the light source) and then compute the total luminous flux in many different directions using luminous intensity data. LISUN has the best goniophotometers for luminance measurement . According to LM-79 Clause 9.3.1, only the type C goniophotometer may be approved with a moving detector.

The photometer head in this kind of goniophotometer is fixed and placed in the optical axis line. The light source is examined, and the photodetector regular enters a specific angle of the cone. The lamp needs to move around, and the mirror revolves around the tested luminaire and reflects the optical signal into the sensor. Therefore, the motion airflow has a more negligible effect on the lamp temperature of goniophotometers of this kind.

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