Why is lm-79 the standard for street light measurements

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 LM-79 Intensity measurements are luminous intensity (measured in candela) taken from various angles all around an LED light source. It can combine this group of candela values to calculate zonal or total lumens, which may be used to make illuminance predictions within an application.

The LM-79 standard is used mainly for measuring light by how it is perceived by the human eye (photometry or photometric measurement). The standard outlines the testing apparatus, procedures, and circumstances it must follow to make precise and repeatable measurements of the amount of light produced by LED goods and the amount of electrical power such products use.

Generally, it may break down the testing techniques into two categories: angularly scanned and integrated (also known as goniometer measures) and measurements that use integrating spheres. This standard's very first iteration had the number.

LM-79-08, and it was released to the public in the year 2008. The updated version of the standard, denoted by the number LM-79-19, was released in 2019. This version increased the restrictions placed on the laboratory settings being tested to improve the repeatability of the results and the level of agreement across individual laboratories within the industry.

 

Light output is measured using a goniophotometer as part of LM-79 (goniophotometry). An example of a goniophotometer in operation measuring the luminous intensity of light emitting diodes (LEDs) in a dark lab, in candelas (cd) and a broad range of angles around the light source. The goniophotometer is designed only to measure the light coming from certain angles rather than taking an overall reading.

It must block any remaining illumination from the fixture (usually by using carefully positioned baffles and light-absorbing materials). A UGR test machine measures the light's intensity throughout a range of candela values or its distribution. Imagine a sphere of measuring lights shining back at the person being tested.

All candela readings are then exported as IES files, which can be read by a wide variety of lighting application programs and used to make estimates of the illuminance (footcandle or lux) that the luminaire will produce after it is mounted. The lumen output (lm) and directional brightness (cd) may both be calculated from the sphere of candela readings.

Luminous efficiency (lm/W) is the amount of light output relative to the energy used to create that light. Beam angle, beam spread, field angle, field spread, cone of light, circle of light, and coefficients of utilization tables (CU tables) are all derived from the cd measurements.

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