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Talking Photometry: Are Halogens History?

Recent press reports have forecast the demise of the popular halogen spotlight as a result of proposed EU energy efficiency regulations. To determine whether a variety of off-the-shelf, low voltage halogen lamps would fall foul of the rules, Lighting Magazine asked Photometric Testing to conduct tests to assess the lamps’ compliance with the proposed regulations. The results were – shall we say – “illuminating”. Let us explain.

GU10 Many will already be familiar with the luminous efficacy of a lamp or luminaire. This is a measure of the electrical to optical efficiency of a lamp and is calculated as the ratio of the light emitted (luminous flux in lumens) to the electrical power consumed (Watts), quoted in lumens per Watt. However for directional lamps, what matters is not how much light is produced overall, rather where the light goes. Directive 2010/30/EU of the European Parliament defines a “directional lamp” as a lamp that has at least 80% light output within a solid angle of pi steradians (a 120° cone). For directional lamps (such as GU10, MR16 etc), the EU have defined a new metric which is called “useful lumens”. The useful lumens from a directional halogen lamp is that luminous flux emitted within a 0.5 pi steradian (90°) cone.

The lighting industry’s concern with the draft regulations is based on the fact that the EU has also proposed that its energy labelling requirements are aligned with an existing directive, 2009/125/EC. This will mean that directional lamps and LEDs are included in eco-design regulations. Consequently, these lamps will now have to comply with the minimum energy efficiency measures stated in the directive and this will mean that some of the least efficient directional lamps will have to be removed from sale in the European market, over the next 1-4 years.

You might assume that the EU would be happy to gauge lamp efficiency using the well established luminous efficacy metric. Of course life is never simple and the EU have defined another new parameter called the Energy Efficiency Index (EEI). EEI rates the amount of optical lumens emitted compared to the electrical Watts consumed, but just to be contrary, EEI is based upon the modified Watts consumed divided by the modified lumens emitted, which is effectively the reverse of luminous efficacy. This means that the lower the EEI, the higher the efficiency of the lamp. We are sure there is a good reason for this counter-intuitive approach, but do let us know if you figure this one out.

The EU has defined EEI as ranging from ≤ 0.11 for class A++ lamps (the most efficient) to > 0.95 for class E lamp (the least efficient). The EU energy efficiency regulations will require that directional lamps satisfy EEI class B or better, with lamps achieving a rating of class C or worse having to be removed from sale, phased over the 2013-2016 period. What is not clear is which lamps will achieve the minimum efficiency necessary to satisfy the planned regulations (class B or higher) and which will have to be removed from sale (class C or lower). This uncertainty is based upon the simple fact that useful lumens (and hence EEI) are not currently measured or specified by the majority of lamp manufacturers. The EU has defined a new metric and it is impossible to calculate the proportion of useful lumens from a particular lamp based upon its total flux (lumen output). This is why Lighting Magazine turned to Photometric Testing for help in establishing whether a selection of commercially available low voltage halogen lamps would satisfy the minimum energy efficiency requirements likely to be set by the EU.

We determined the useful lumens of each of four sample lamps using a specialised piece of equipment called a goniophotometer. A goniophotometer tilts the test lamp horizontally and vertically one angle at a time and records the luminous intensity in candelas from the lamp at each angle. In goniophotometry, the sum of the luminous intensity values recorded at each angle gives the total luminous flux in lumens from a lamp. The useful lumens for directional filament lamps is defined as the total of the directional intensity values emitted into a solid angle of 0.5 pi steradians (90° cone). For other lamp types with beam angles of greater than 90°, the useful lumens are those which are emitted into an angle of 1.0 pi (120° cone).

Whereas total luminous flux can be measured with an integrating sphere, the useful lumens from a lamp cannot be determined using a simple sphere test – this only gives the sum of all of the light emitted in all directions. It is not possible to calculate the directional intensity at each angle nor the partial (useful) flux emitted into a 90° cone from a sphere test. To determine useful (90°) luminous flux, it is necessary to use  a goniophotometer to measure the luminous intensity at each angle and compute the useful lumens emitted into a 90° cone.

Photometric Testing connected each of the test lamps to a standard 12V halogen lamp power supply, which in turn was connected to a regulated mains supply. The electrical power consumption was recorded using a power meter whose calibration was traceable to the UK’s National Physical Laboratory (NPL) via a UKAS accredited calibration. The goniophotometer that was used to measure the intensity at each angle was calibrated against a reference photometer that is also traceable to the UK’s National Physical Laboratory (NPL) via a UKAS accredited calibration. The sum of the directional intensities recorded by the goniophotometer over 2 pi steradians (180° cone) was calculated and compared to an integrating sphere measurement of the total lamp flux – results agreed to an average of 0.2%, which served to validate the goniophotometer values.


Sample Total Flux (lumens) Useful Lumens (lumens, 90°) Ratio Useful:Total Lumens (%)
Efficacy (lumens/Watt) EEI Class
A 604.9 557.1 92.1 11.7 1.16 C
B 579.3 538.7 93.0 14.9 0.87 B
C 559.7 539.6 96.4 11.3 1.12 C
D 539.9 475.7 88.1 14.5 0.93 B

The results of the tests are shown in the table above. It is interesting to note that the lamp with the highest luminous flux (sample A) also had the second lowest luminous efficacy and the worst EEI. This was a generic, low cost lamp purchased from a discount retailer. This achieved a class C rating so will be banned under the proposed EU regulations. The lamp with the highest proportion of useful lumens to total lumens (sample B) also achieved the highest luminous efficacy and the best EEI of the group. This lamp was awarded a class B rating and would survive the EU’s purge of the least efficient lamps. The 3 samples from major brand manufacturers all came out ahead of the “discount” lamp, however, one of the branded lamps still failed to achieve the necessary minimum EEI would fail to meet the EU’s efficiency criteria. So paying extra for a branded lamp from a major manufacturer is no guarantee of the highest efficiency.
The EU regulations are expected to come into effect in autumn 2012, which means that they would come into legal force from September 2013. The likely phase-out schedule of inefficient lamps will depend upon the type of lamp and its exact EEI rating. According to Lighting Magazine, directional incandescent reflector lamps and low efficiency mains voltage halogens are likely to be phased out in 2013-2014. The least efficient low voltage halogens are likely to be banned from 2013 while higher performance mains voltage halogens are due to follow in 2016. Quality, conventional low voltage halogens are expected to be phased out in 2013-2014. This just leaves the higher efficiency low voltage halogens with infra-red coated reflectors and/or xenon gas fills as the surviving halogen technology available after the full implementation of the EU rules.

About Photometric Testing

Photometric Testing is a specialist lighting test laboratory based at Upper Rissington in Gloucestershire. The company provides independent testing of LEDs, luminaires and lamps that are traceable to national standards and performed in strict accordance with applicable international guidelines and industry best practice. From standard photometric data to photobiological safety testing, and from training courses in light measurement to developmental testing of new products, Photometric Testing helps its clients save time and money and bring the next generation of ultra efficient lighting products to market more quickly. Photometric Testing has invested in a temperature controlled dark room and the latest, state-of-the-art photometric, spectroradiometric and goniophotometric equipment to ensure that its measurements are accurate, repeatable and conform to the latest international lighting standards. This investment has lead to the creation of what is probably the most up-to-date lighting test laboratory in the UK.