The present report highlights the main differences found between the standards:
- IESNA LM-79-08 (American norm) and
- EN 13032-4: 2015 (European norm)
on photometric and colorimetric measurements of LED luminaires and sources.
It must be said that the European standard, which was published 7 years later with respect to the corresponding American standard, has taken advantage of the experience gained in recent years and represents nowadays a significant step forward with respect to the American one.
The main differences between the two standards are reported below:
1.1.1 Photometry and colorimetry
A difference that is immediately evident is the different way in which Americans and Europeans refer to photometry and colorimetry. For Americans photometry consists of both photometry and colorimetry together (colorimetry is nothing more than an attribute of the photometry) whereas Europeans separate these 2 things cleanly, with photometry on one side and colorimetry on the other.
1.1.2 Measuring instruments
The largest and most obvious difference between the two standards is that:
- according to LM-79-08, measurements are to be made using Type C goniophotometers only, that is to say:
- Mirror goniophotometers: the standard doesn’t specify if it needs to be a luminaire rotating goniophotometer with the mirror revolving around the central axis mirror-photocell or a mirror rotating goniophotometer with the luminaire rotating around the vertical axis
- Sensor revolving goniophotometers
- EN 13032-4:2015 allows instead the use of any type of machine, including luminaire revolving goniophotometers. In this last case it is important that the operators indicate the conditions in which the measurement is to be carried out and that they verify that there are no variations (in light flux, for instance) during the same.
The diversity between the 2 standards is the result of a long series of photometric measurements carried out on several different types of machines (mirror goniophotometers, luminaire revolving goniophotometers, etc.) starting in 2009 – a related article is available on OxyTech’s website (http://www.oxytech.it/PDF/LEDin%20-%20Rilievi%20LED%20-%20Rv01%20070212%20-%20Ita.pdf):
Photometric measurement of LED luminaires (the article was published in LEDin magazine, February 2012).
1.1.3 Spectrometric/colorimetric parameters calculation
Another major difference regards the method used for the calculation of colour parameters (CCT, CRI, Delta(u’, v’) etc.) obtained from a goniophotometer measurement (a different method would be that of using a sphere, which is however not able to determine all the required parameters such as Delta (u’,v’)):
- standard LM-79-08 requires that measurements carried out on a Type C Goniophotometer in several C-Gamma points are then integrated by means of a weighted average whose weight is given by the intensities detected at each C-Gamma point of the measurement
- EN 13032-4 requires instead that the weight is estimated in radiance, that is to say, the actual energy involved on the basis of each wavelength and in each C-Gamma position. In this case, the evaluation is more precise
1.1.4 Measurement uncertainty calculation
EN 13032-4 includes the exact definition of the method to be used for the evaluation of the measurement uncertainty of the laboratory where the tests are carried out, whereas LM-79-08 simply refers to external standards (see regulatory and bibliographical references in sections 5 and 6 on page 14).