Source Lumen VS Fitting Lumen: unveiling the truth

Over the past number of years competition for lighting projects has become fierce with the addition of many new competitors every year. One of the most obvious examples of this is the number of lighting manufacturers in a country like China, where there are thousands of LED lighting manufacturers. Every lighting manufacturer is trying to get a piece of the market and seem to have no limitations on the extent to which they will go to achieve sales. Many lighting manufacturers will compromise the quality of raw materials, LED chips, LED drivers, housings, and optics to reduce the selling price. Take for example the driver supplied by a manufacturer below.

For many people, I would dare to say most people, one of the most frustrating and annoying things is to feel deceived or lied to. Many people react to lies and deceit through breaking off permanent contact or never extending trust again. Unfortunately, the lighting industry is fraught with information that is not true and that is used to create performance perceptions. One of the most common areas of deceit is the declared lumen output of LED fittings. In this blog we will discuss some of the key observation points when determining the lumen output of an LED fitting. In order to do this, we need to clarify the basic definition of Lumen. What is Lumen? The luminosity, or flux, of a light source is a measure of the total quantity of visible light emitted by the light source in a given time period. This flux is measured in lumen, and is different from the power of a light source, which is the radiant flux, which includes all electromagnetic waves emitted by the light source. One lumen is the amount of light emitted by a light source every square meter over a given period of time. When measuring the LED flux there are three specific measurements that are used within the industry the first being LM80 , LM79 and TM21. In the descriptions below each of these tests are explained. LM80 is designed to test the LED CHIP in isolation from the fitting. LM79 is designed to test the FITTING as a complete fixture, with all hardware, chips, optics, and electronics.

TM21 outlines a standard calculation method to predict future lumen depreciation using LM-80 data. Whats the difference between “Source lumen” and “Fitting lumen”? When studying data sheets one of the key performance parameters that are evaluated is the lumen output. In order to generate a perception of performance many lighting suppliers declare the source lumen or led lumen or chip lumen, instead of declaring the fitting lumen. After all consumers purchase a light for the amount of lumen that radiates from the fitting NOT the amount of light within the fitting. The source lumen is of little interest to the consumer.

Many lighting suppliers declare the source lumen for commercial purposes only. By declaring the source lumen, the lighting supplier presents the perception of a higher performing light which will sway the decision to purchase a specific light compared to another. The source lumen is calculated by using the LM80 data and multiplying the data by the number of chips that have been installed or mounted in a specific fitting. This, methodology however does not take into consideration any losses of light with the addition of increased heat, optics, electronics, diffusers, drivers, and heat sinks. Every one of these factors plays a part in the fitting lumen output. The accurate measurement of lumen output is done using LM79 testing standards that takes the entire fitting into account.

By definition, lumen is described as the luminosity, or flux, of a light source is a measure of the total quantity of visible light emitted by the light source. If therefore, the source lumen is not (1) visible and (2) emitted, it should not be declared as lumen at all.

In other words, source lumen in NOT Lumen. Why then are lighting suppliers declaring source lumen other than for commercial gain? If lighting suppliers have done the LM79 test (whole fitting) and the TM21 test, why would they declare source lumen if not for creating performance perceptions? Further, if LM79 and TM 21 tests are not performed, how is it possible to declare not only lumen output but also projected life? Why are lighting suppliers declaring the fitting lumen in the fine print at the bottom of the data sheets?

Conclusion It is advisable for parties interested in either specifying or procuring lights for professional projects both for commercial and industrial use, to do a thorough evaluation of the lumen output. Reputable or quality LED lighting suppliers will typically declare the LM79 (Fitting) lumen output. Please feel free to contact Genesis One Lighting for your lighting needs and requirements. sales@genesisone.co.za Below the descriptions of LM80/ LM79/ TM21 LM80 This Approved Method provides the methods for measurement of luminous flux and color maintenance for LED packages, arrays, and modules. It covers luminous, radiant, or photon flux maintenance and color maintenance, including changes in chromaticity coordinates, peak wavelength, or centroid wavelength versus time. The maintenance characteristics are measured under controlled conditions that allow direct comparison of results obtained at different laboratories. LM79 LM-79 is a standard that defines how the performance of an LED fixture should be measured. A test according to LM-79 is carried out at a point in time and at a single temperature. LM-79 is important to lighting designers, specifiers, and manufacturers. It provides a standard method of testing LED fixtures so that the data from different brands and models can be directly and objectively compared.

The optical data gathered during a photometric test compliant with LM-79 will typically include the following:

• Total luminous flux (lumens, lm)

• Luminous efficacy (lumens/watt, lm/W)

• Luminous intensity in one or more directions (candelas, cd)

• Chromaticity coordinates

• Correlated colour temperature (kelvin, K)

• Colour rendering index (rendering average, Ra)

LM-79 only relates to complete LED lamps or LED luminaires.

TM21

LEDs, are alike other light sources, see their output decline over time. However, given the remarkably longer life of LEDs and the absence of visible signs indicating their decreasing performance, it can be more complex to accurately measure and communicate light output over time. To help address this issue, the Illuminating Engineering Society of North American (IESNA) and the Environmental Protection Agency (EPA) have put in place standards for reporting the useful lifetime of an LED package: LM-80 (Measuring Luminous Flux and Color Maintenance of LED Packages, Arrays and Modules) and TM-21(Projecting long term Lumen Maintenance of LED Light Sources).

TM-21 outlines a standard calculation method to predict future lumen depreciation using LM-80 data.