BENCH TEST / LED MODULES
LED modules seem to be all the rage but how do they perform, are they useful and what will the future hold? Our LED Expert, Dr Geoff Archenhold, puts the big four front runners to the test.
THIS IS A MODULE WORLD
In the rush to meet the market demands for LED lighting, many lighting fixture manufacturers are finding it extremely difficult to produce high quality LED lighting fast enough. So will LED modules provide a quick fix to their predicament or will they become the long term solution for a more sustainable LED lighting industry? This month we take a look at some of the leading LED modules available on the market and evaluate their optical and efficiency performance to see how far they have come...
Leading LED module manufacturers were invited to submit 1000 lumen, 3000K samples to the Lighting Association Laboratories in Telford, UK. Worryingly, only four were able to fit the criteria. Whether this was due to error or a lack of willingness to take part is open to question. There were two main categories of photometric testing undertaken for each light module: 1) Lumen Output 2) Spectral Power Distribution – CCT and CRI
Each of these measurements were taken at the UKAS accredited laboratories and, to ensure that all measurements were taken consistently, the ambient temperature in which measurements were taken was maintained at 25°C ± 1°C.
The Lumen Output was determined for each module by placing it ‘cap-up’ at the top of a 1.8 metre Integrating Sphere. Referring to the test equipment schematic, a correction factor for each sample was taken in order to make allowances for the absorption of inter-reflected light within the sphere. The correction factor is determined by the use of a calibrated and known auxiliary lamp mounted behind a baffle within the sphere.
Each module sample was then switched on and allowed to stabilise. In our tests a module was deemed to be stable when the variation of at least three readings of the light output (Lumens) over a 30 minute period, taken 15 minutes apart, is less than 0.5% of the total light output from the
engine. Each module sample was operated using a stabilised power supply at 230V (±1V). The lumen output of the sample was monitored (observed using software graph display) and a lumen output reading was recorded every minute until stable. The stabilised lumen output is calculated from the average of three readings recorded 15 minutes apart during the stable 30 minute period. Power measurements were taken regularly at 10 minutes intervals starting at 5 minutes (i.e. at 5 min, 15 min, 25 min…etc.) and included the total input power along with the Power Factor Correction figures measured by the Yokogawa PZ4000 Power Analyser.
The Spectral Power Distribution (SPD) measurements are required to accurately derive the Correlated Colour Temperature (CCT) and Colour Rendering Index (CRI) for all of the light engines and a schematic of the system used within the tests are shown. In order to measure the SPD of each sample they were then measured using a spectroradiometer (a spectral correction factor was measured prior to lumen output measurements using an auxiliary lamp in the same way in order to provide a traceable calibration reference point).
Following this, three spectral scans (with a wavelength step size of 2nm) were taken for each module. Using dedicated software, the spectral data for the three scans were then averaged and used to determine the Chromaticity Co-ordinates, CCT and CRI (Ra) of each sample.
For reference the calibrated equipment used included:
• Bentham 1.8m sphere • Bentham 487/417 Current Amplifier Integrating ADC • Bentham TMc300 Monochromator • Bentham 605 Current Stabilised Power Supply • Yokogawa PZ4000 Power Analyser.
(That’s enough of the detail, now turn over to see the results...)
Paul Gilmartin of the Lighting Association Laboratories places an LED module in the Bentham 1.8m sphere prior to testing.
TECHNOLOGY / BENCHTEST 097
A schematic of the measurement equipment used to determine the Lumen output of the LED modules.
A schematic of the measurement equipment used to determine the chromaticity coordinates, CRI and CCT of the LED modules.
The Yokogawa PZ4000 Power Analyser used for Power & PFC measurement.
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