Question from Voltimum user: "Are there any quality criteria available by which I can judge the difference between LED luminaires? When getting quotes from different suppliers, there can be substantial price differences and it would be good to know what to look for."
Answer provided by Jacek Lipiec, Technical & Commercial Manager - New Technologies, Sylvania.
The IEC published two Public Available Specification (PAS) performance requirement documents dealing with LED products:
• IEC/PAS 62717 Performance requirements – LED modules for general lighting
• IEC/PAS 62722 Performance requirements – LED luminaires for general lighting
These were developed together to provide:
• the definition of a set of quality criteria related to the initial specifications of a product;
• a standardised description on how to measure these quality criteria.
To ensure consistency in quality criteria, definitions and measuring methods, most of these are defined in IEC/PAS 62717. The luminaire standard IEC/PAS 62722 under certain conditions allows the use of compliant modules to reduce the number of tests for LED luminaires. This makes manufacturers claims of initial specifications of LED- modules and luminaires comparable.
A reputable manufacturer of quality LED products should have no hesitation in being readily able to supply prospective customers with any information pertaining to the list of quality criteria that should be considered when evaluating manufacturer’s claims:
Rated input power: the rated input power shows the amount of energy consumed by a luminaire, including its power supply. It is expressed in watts.
Rated luminous flux: This is the light emitted by the luminaire which is expressed in lumens. For traditional (non LED) luminaires it is usual that Relative values are measured and multiplied by the lamp flux. For ‘LED’ luminaires it is recommended that Absolute photometric values are used. Absolute photometry results in a LOR=1.
LED luminaire efficacy: The measured initial luminous flux divided by the measured initial input power of the same individual LED luminaire. It is expressed in lumens per watt.
Luminous intensity distribution: The spatial distribution of the luminous flux graphically depicted in a luminous intensity distribution curve, which is usually expressed in a polar diagram representing the light intensity as a function of angle about a light source. It is expressed in cd.
Correlated Colour Temperature (CCT): Although white light is a mixture of colours, not all whites are the same since they depend on their constituent colours. So a white with a higher proportion of red will appear warmer and a white with a higher proportion of blue will appear cooler. In order to classify the different types of white light, the concept of colour temperature is applied which is described as the colour impression of a perfect black-body radiator at certain temperatures. This concept can be best explained with the help of familiar thermal radiators like the filament of an incandescent lamp or an iron bar. When these materials are heated to a temperature of 1000 K their colour appearance will be red, at 2000-3000 K they will look yellow white, at 4000 K neutral white, and at 5000-7000 K cool white. The higher the colour temperature, the cooler the perception of the white light becomes. It is expressed in Kelvin. The initial CCT value classification for the photometric code can be obtained by taking the initial CCT value divided by 100.
Rated Colour Rendering Index (CRI): Although light sources may have the same colour appearance, this doesn’t necessarily mean that coloured surfaces will look the same under them. Two lights that seem to have the same white colour appearance may be the result of different blends of wavelengths. As a result a given material may appear differently since the surface may not reflect the constituent wavelengths by the same extent. Its colour appearance will change when it is exposed to one or other light. So, colour rendering is an important criterion when selecting light sources for lighting application solutions. However with new LED technology coming in, with a narrow spectrum, the CRI index is not in all circumstances giving a fair representation of the colour appearance. The rule of thumb though is that the higher the number, the better the colour rendering.
Lumen maintenance code: As the typical life of a LED luminaire is long, it is time-consuming to measure the actual lumen reduction over life. Also the actual LED behaviour with regard to lumen-maintenance may differ considerably by type and manufacturer. It is not possible to express the lumen-maintenance of all LEDs in simple mathematical relations. A fast initial decrease in lumen output does not automatically imply that a particular LED will not make its rated life. In order to validate a life time claim, an extrapolation of test data is needed. In the IEC a general method of projecting measurement data beyond limited test time is under consideration. In the US an extrapolation based on LM-80 test data will be described in IES TM-21. Instead of life time validation, the IEC/PAS has opted for lumen maintenance codes at a defined finite test time. Therefore, the code number does not imply a prediction of achievable life time. The maintained luminous flux is measured at 25% of rated life time up to a maximum of 6.000 hours and expressed as a percentage of the initial value. The maintained value determines the lumen maintenance code.
Rated life (in h) of the LED module and the associated rated lumen maintenance (Lx): The length of time expressed in hours, during which a population of LED modules provides more than the claimed percentage (x) of the initial luminous flux always published in combination with the failure fraction. The recommended series of values for (x) is 70, 80, 90.
Failure fraction (By), corresponding to the rated life of the LED module in the luminaire: The percentage (y) of a number of LED modules of the same type at their rated life that have failed. This failure fraction expresses the combined effect of all components of a module including mechanical, as far as the light output is concerned but as LED modules do not generally fail, the values are indicative only with the recommended series of values for (y) as B10, B50.
Ambient temperature (ta) for a luminaire: The ambient temperature around the luminaire related to the specified performance. For a given performance claim the ambient temperature (ta) is a fixed value. It is possible to specify performance claims at different ambient temperatures. If the LED luminaire is to be used at an ambient temperature different to that at which it was tested, correction factors will need to be applied to the performance criteria. It is expressed in degrees Celsius with the most common ambient temperature for general use Ta=25 degrees C.
Power Factor: The power factor should be clearly stated in all cases. Although product standards may not require this below 26W, in Australia, the recommended power factor is PF>0.9 for commercial applications, PF>0.7 for Residential applications.
Intensity Distribution: Photometric data is available in two formats. Absolute Photometry does not require the use of a separate lumen output for the light source. Relative Photometry requires the LED package flux to be quoted. Both methods produce the same result. For LED luminaires Absolute photometry shall be used. Absolute photometry of LED luminaires should be conducted according to IES LM-79-08 Photometric Measurements of Solid-State Lighting Products. Relative photometry should be conducted according to EN13032-1 (2004) Light and Lighting Measurement and Presentation of Photometric Data of Lamps and Luminaires - Part 1: Measurement and file format. These standards contain advice on measurement uncertainty. Photometric results that are calculated by deviation from the tested sample by the use, for example of higher or lower drive currents or dies from bins other than the bin used for the tested device are to be clearly identified as such. Correction factors used are to be provided with the results.
Drive Current: For proper operation, the power supply and electronics must provide a well‐controlled DC drive current. Drive current affects LED operating temperature and thus life and output. The higher the LED is driven the brighter it will be but it may have a shorter operation lifetime and be less efficient. Some of the new multi die LEDs are designed to operate and perform at higher drive currents. Declaration of the drive current is important when remote drivers are used.
Optical Risk: Some countries have adopted an optical risk factor which sets a standard for worker exposure to optical radiation. For example, the Control of Artificial Optical Radiation at Work Regulations 2010 apply to light emitted from all artificial light sources including LEDs. These regulations require employers to protect the eyes and skin of workers from exposure to hazardous sources of artificial optical radiation. Exposure limits defined in the standard EN‐62471 are in European regulation (directive 2006/25/CE). These are a combination of source power and exposure time.
The IEC published two Public Available Specification (PAS) performance requirement documents dealing with LED products:
• IEC/PAS 62717 Performance requirements – LED modules for general lighting
• IEC/PAS 62722 Performance requirements – LED luminaires for general lighting
These were developed together to provide:
• the definition of a set of quality criteria related to the initial specifications of a product;
• a standardised description on how to measure these quality criteria.
To ensure consistency in quality criteria, definitions and measuring methods, most of these are defined in IEC/PAS 62717. The luminaire standard IEC/PAS 62722 under certain conditions allows the use of compliant modules to reduce the number of tests for LED luminaires. This makes manufacturers claims of initial specifications of LED- modules and luminaires comparable.
A reputable manufacturer of quality LED products should have no hesitation in being readily able to supply prospective customers with any information pertaining to the list of quality criteria that should be considered when evaluating manufacturer’s claims:
Rated input power: the rated input power shows the amount of energy consumed by a luminaire, including its power supply. It is expressed in watts.
Rated luminous flux: This is the light emitted by the luminaire which is expressed in lumens. For traditional (non LED) luminaires it is usual that Relative values are measured and multiplied by the lamp flux. For ‘LED’ luminaires it is recommended that Absolute photometric values are used. Absolute photometry results in a LOR=1.
LED luminaire efficacy: The measured initial luminous flux divided by the measured initial input power of the same individual LED luminaire. It is expressed in lumens per watt.
Luminous intensity distribution: The spatial distribution of the luminous flux graphically depicted in a luminous intensity distribution curve, which is usually expressed in a polar diagram representing the light intensity as a function of angle about a light source. It is expressed in cd.
Correlated Colour Temperature (CCT): Although white light is a mixture of colours, not all whites are the same since they depend on their constituent colours. So a white with a higher proportion of red will appear warmer and a white with a higher proportion of blue will appear cooler. In order to classify the different types of white light, the concept of colour temperature is applied which is described as the colour impression of a perfect black-body radiator at certain temperatures. This concept can be best explained with the help of familiar thermal radiators like the filament of an incandescent lamp or an iron bar. When these materials are heated to a temperature of 1000 K their colour appearance will be red, at 2000-3000 K they will look yellow white, at 4000 K neutral white, and at 5000-7000 K cool white. The higher the colour temperature, the cooler the perception of the white light becomes. It is expressed in Kelvin. The initial CCT value classification for the photometric code can be obtained by taking the initial CCT value divided by 100.
Rated Colour Rendering Index (CRI): Although light sources may have the same colour appearance, this doesn’t necessarily mean that coloured surfaces will look the same under them. Two lights that seem to have the same white colour appearance may be the result of different blends of wavelengths. As a result a given material may appear differently since the surface may not reflect the constituent wavelengths by the same extent. Its colour appearance will change when it is exposed to one or other light. So, colour rendering is an important criterion when selecting light sources for lighting application solutions. However with new LED technology coming in, with a narrow spectrum, the CRI index is not in all circumstances giving a fair representation of the colour appearance. The rule of thumb though is that the higher the number, the better the colour rendering.
Lumen maintenance code: As the typical life of a LED luminaire is long, it is time-consuming to measure the actual lumen reduction over life. Also the actual LED behaviour with regard to lumen-maintenance may differ considerably by type and manufacturer. It is not possible to express the lumen-maintenance of all LEDs in simple mathematical relations. A fast initial decrease in lumen output does not automatically imply that a particular LED will not make its rated life. In order to validate a life time claim, an extrapolation of test data is needed. In the IEC a general method of projecting measurement data beyond limited test time is under consideration. In the US an extrapolation based on LM-80 test data will be described in IES TM-21. Instead of life time validation, the IEC/PAS has opted for lumen maintenance codes at a defined finite test time. Therefore, the code number does not imply a prediction of achievable life time. The maintained luminous flux is measured at 25% of rated life time up to a maximum of 6.000 hours and expressed as a percentage of the initial value. The maintained value determines the lumen maintenance code.
Rated life (in h) of the LED module and the associated rated lumen maintenance (Lx): The length of time expressed in hours, during which a population of LED modules provides more than the claimed percentage (x) of the initial luminous flux always published in combination with the failure fraction. The recommended series of values for (x) is 70, 80, 90.
Failure fraction (By), corresponding to the rated life of the LED module in the luminaire: The percentage (y) of a number of LED modules of the same type at their rated life that have failed. This failure fraction expresses the combined effect of all components of a module including mechanical, as far as the light output is concerned but as LED modules do not generally fail, the values are indicative only with the recommended series of values for (y) as B10, B50.
Ambient temperature (ta) for a luminaire: The ambient temperature around the luminaire related to the specified performance. For a given performance claim the ambient temperature (ta) is a fixed value. It is possible to specify performance claims at different ambient temperatures. If the LED luminaire is to be used at an ambient temperature different to that at which it was tested, correction factors will need to be applied to the performance criteria. It is expressed in degrees Celsius with the most common ambient temperature for general use Ta=25 degrees C.
Power Factor: The power factor should be clearly stated in all cases. Although product standards may not require this below 26W, in Australia, the recommended power factor is PF>0.9 for commercial applications, PF>0.7 for Residential applications.
Intensity Distribution: Photometric data is available in two formats. Absolute Photometry does not require the use of a separate lumen output for the light source. Relative Photometry requires the LED package flux to be quoted. Both methods produce the same result. For LED luminaires Absolute photometry shall be used. Absolute photometry of LED luminaires should be conducted according to IES LM-79-08 Photometric Measurements of Solid-State Lighting Products. Relative photometry should be conducted according to EN13032-1 (2004) Light and Lighting Measurement and Presentation of Photometric Data of Lamps and Luminaires - Part 1: Measurement and file format. These standards contain advice on measurement uncertainty. Photometric results that are calculated by deviation from the tested sample by the use, for example of higher or lower drive currents or dies from bins other than the bin used for the tested device are to be clearly identified as such. Correction factors used are to be provided with the results.
Drive Current: For proper operation, the power supply and electronics must provide a well‐controlled DC drive current. Drive current affects LED operating temperature and thus life and output. The higher the LED is driven the brighter it will be but it may have a shorter operation lifetime and be less efficient. Some of the new multi die LEDs are designed to operate and perform at higher drive currents. Declaration of the drive current is important when remote drivers are used.
Optical Risk: Some countries have adopted an optical risk factor which sets a standard for worker exposure to optical radiation. For example, the Control of Artificial Optical Radiation at Work Regulations 2010 apply to light emitted from all artificial light sources including LEDs. These regulations require employers to protect the eyes and skin of workers from exposure to hazardous sources of artificial optical radiation. Exposure limits defined in the standard EN‐62471 are in European regulation (directive 2006/25/CE). These are a combination of source power and exposure time.
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