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Photometry Testing: A Scientific Measurement Methodology of Perceived Brightness of Light to Human Eye

Saurabh Srivastava, Manager – Business Development, Products|TÜV Rheinland India

The measurement of quality and quantity of light absorbing analyte in a solution is the basic principle of Photometry technology. This technologydescribes the process of safety measures which is observed in performing reproducible measurements of total luminous flux, electrical power, luminous intensity distribution, and chromaticity, of solid-state lighting (SSL) products for illumination purposes under standard conditions. It covers LED-based SSL products with control electronics and heat sinks incorporatedin those devices that require only AC mains power or a DC voltage power supply to operate. It also covers SSL products in a form of luminaries (fixtures incorporating light source) as well as integrated LED(Light Emitting Diodes) lamps.To ensure safety, manufacturers are now accountable for delivering products and components with the right photometric properties.

warehouse, or any large facilityFor example, to manage a building, warehouse, or any large facility, we need to understand the benefits that indoor lighting can bring. Conventional lights waste a lot of energy that is dissipated as heat instead of light. LED lamps are the latest and most exciting technological advancement in the lighting industry. These are small, solid light bulbs which are extremely energy efficient and long-lasting. There are instruments which are used to measure the intensity of lights by comparing between an unknown intensity and a standard or known intensity. It is all about “brightness perceived by the human eye.” Visual brightness of a light source depends on the amount of radiation it emits and on its spectral composition on the visual response function of the observer viewing it. Every human being has a different visual response. To standardize the process, precise photometry is required.

If we think about a manufacturing warehouse, a cricket stadium or a highway or movie theatre, different spaces require a desired level of lighting. With the help of photometry testing, a lighting designer can simulate whether the proposed lighting is delivering the required intensity. The basic photometric data of a luminaire consist of a set of values of luminous intensity in a different direction, produced by direct photometric measurement.

Measurement of intensity distribution involves photometric and angular measurements using Goniophotometerunder controlled working condition of the luminaire, in terms of electrical and ambient temperature measurements. To characterize visual comfort and SSL product performance, total luminous flux, efficacy, luminous intensity distribution data is used to inform a range of other lighting metrics.To compare two different products, parameters such as luminous intensity distribution, Isocandela power, beam angle, LOR andutilization factor table are required.

Measurement of intensity distribution involves photometric

Integratingsphere describes color characteristics,total radiant power (spectral content) of SSL products, from which chromaticity coordinates, Correlated Color Temperature (CCT), and Color Rendering Index (CRI) can be derived. Typically, a product’s Spectral Power Distribution (SPD) is presented in a graph format, which allows the viewer to evaluate the relative amount of radiant power across the range of wavelengths in the visible spectrum (expressed in nanometers, nm), or approximately380 – 780 nm.

The photometric test reports can be useful for preliminary product screening. An experienced user will be able to detect potential challenges in terms of uniformity and glare for an appropriate distribution of a specific application. A product cannot be simply characterized as low or high performance. To overcome this gap, geometric parameters, reflectance characteristics of illuminated surfaces lighting software can be used.The data garnered from Photometry testing enables a complete analysis to ensure requirements are fulfilled.

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TÜV Rheinland offers state-of-the-art testing services to ensure lightingproducts complies with the prescribed safety standards, and are of high quality. We provide a competitive advantage through our neutral and internationally recognized test mark. TÜV Rheinland conducts test on energy efficiency, usability and safety of lighting products, whether lamps, lights, and LEDs are designed for personal or industrial use, with mains power or run on batteries. We provide support ranging from intermediate testing during product development to the international approval of your products. Certification with our test mark enables our customers to access national and international markets quickly. TÜV Rheinland stands for quality and safety for people, technology and the environment.

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