Unlike previous lighting requirements, LED testing has become more stringent and complicated, and involves a significant number of tests for various lighting characteristics. From measuring lumen output, efficacy, correlated color temperature (CCT), color rendering index (CRI), and photometrics to calculating life spans, MaxLite has advanced its rigorous procedures of testing and inspection in the new world of solid-state lighting.
Previous requirements or relative photometry for testing a fixture with lamps required that the lamps be “seasoned” for 100 hours prior to testing when installed in the luminaire as a system, to determine its total lumen output. LED luminaire testing (LM79) tests the entire luminaire with minimal stabilization of the luminaire, thus creating an absolution photometry – the absolute lumen output of the luminaire with the lamp installed and measured. Individual lumen and efficiency are not reported.
MaxLite tests for electrical and photometric measurements of its LED lamps and luminaires (the complete product) to meet IES LM-79 standards and procedures for performing reproducible measurements of LED properties, including: total luminous flux, luminous intensity distribution, electrical power, luminous efficacy and color characteristics such as CRI, CCT and chromaticity. The scope of LM-79 applies to LED products that incorporate control electronics and heat sinks. LM-79 testing requires complete luminaire testing on an absolute photometric basis. However, for solid-state lighting products, the LED lamps typically cannot be separated from their luminaires.
Well-equipped testing labs utilize an integrating sphere and goniophotometer to complete LM79 testing. Lumen output is measured by using an integrating sphere where photometers take measurements of total luminous flux. A goniophotometer is a device used for measurement of the light emitted from an object at different angles. Its use has been increasing in recent years with the introduction of LED-light sources, which are mostly directed light sources and the spatial distribution of light is not homogeneous.
The integrating sphere, also known as an Ulbricht sphere, is an optical component consisting of a hollow spherical cavity, with its interior covered with a diffused white reflective coating, with small holes for entrance and exit ports. Its relevant property is a uniform scattering or diffusing effect. Light rays incident on any point on the inner surface are, by multiple scattering reflections, distributed equally to all other points. The effects of the original direction of light are minimized. An integrating sphere may be thought of as a diffuser which preserves power but destroys spatial information and is typically used with some light source and a detector for optical power measurement.
A similar device is the focusing or Coblentz sphere, which differs in that it has a mirror-like (specular) inner surface rather than a diffuse inner surface. The practical implementation of the integrating sphere was due to work by R. Ulbricht (1849–1923) published in 1900, and it has become a standard instrument in photometry and radiometry. The sphere has an advantage over a goniophotometer for measuring the light produced by a source so that total power can be obtained in a single measurement.
The life span of an LED luminaire is measured from an ISTMT (In Situ Temperature Measurement Testing) test, which takes thermal readings at the LED chip and driver. This information, along with testing data from the LED chip manufacturers’ LM80 report, is then calculated using the TM21 calculator from Energy Star, to achieve a life expectancy of the product in a number of hours (eg. 80,000 hours). Information is inputted into a TM21 report from Energy Star for life expectancy of product, and records of all files including LM9, LM79, LM80 and TM21 are available when required by engineers or inspectors.
MaxLite currently works with six testing laboratories – three on each coast – to test and certify LED lamps and fixtures. In addition, the company will open a UL-authorized testing lab in its new LEED-Certified office in Anaheim, California in 2015. They will also expand the West Caldwell, New Jersey headquarters to include a NVLAP-certified lab.
The National Voluntary Laboratory Accreditation Program (NVLAP) provides an unbiased third-party evaluation and recognition of performance. NVLAP accreditation signifies that a laboratory has demonstrated that it operates in accordance with NVLAP management and technical requirements in areas such as quality systems, personnel, accommodation and environment, test and calibration methods, equipment, measurement tractability, sampling, handling of test and calibration items, and test and calibration reports. NVLAP accreditation does not imply any guarantee (certification) of lab performance or test/calibration data; it is solely a finding of lab competence. A lab may cite its accredited status and use the term NVLAP and symbol on reports and in business and trade publications, provided that this use does not imply product certification. For a testing lab to achieve NVLAP certification, it must pass stringent requirements showing its capability of handling and testing products in a manner that is required by the NVLAP-certification process.