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Issue 46 Dec / Jan 2008/9

David Morgan takes a look at a new breed of LED downlights for the commercial market.

ACDC is a specialist lighting company that has built a strong reputation in the specification market based on the development of innovative cold cathode lighting systems. The company first came to notice in the early 1970’s on the TV show ‘Tomorrow’s World’ with an early form of cold cathode electronic control gear.

The company is based in Lancashire with worldwide sales and was an early adopter of high power LEDs. The first generations of LED products from ACDC were mainly for decorative effect and small-scale display lighting but the launch of the Evolution LED downlight range takes ACDC closer into the mainstream commercial lighting market.

The holy grail of LED lighting in recent years has been the creation of a downlight, with good colour rendition, warm white light, that could achieve a system efficiency level of at least 45 lumens per watt including drivers and power supplies losses and an operational life of 50,000 hours to 70% initial lumen levels. This goal has been pursued by lighting companies around the world and in late 2006 Toshiba Lighting in Japan won a competition, organised by the Japanese Government, by achieving this level of efficiency.

ACDC were also engaged in this quest and have recently reached this level of efficiency with their new Evolution range of LED downlights.
The development route that ACDC have taken with the Evolution is an interesting and unusual one. They have focused on the design and development to a high efficiency light engine that is then fitted into the existing Prospex range of halogen downlights produced by Lucent Lighting.

So this product review is in reality a review of a combination of products from two different companies.

The design of the Lucent Pro Spec dowlights is well established and is a very competent product range. The attention to detail throughout the range is good including the adjustment mechanism on the aimable version which works via a spring loaded, screw driver adjustable system. The cones are of high perceived quality and fit into the housings neatly. The trimless housing appears to be well designed for use in plaster ceilings.

The Evolution LED light engine utilises the Luxeon Rebel LED and claims to be one of the first LED downlights to meet the UK Part L energy efficiency requirements with an efficiency of over 45 lumens per watt for warm white and over 80 lumens per watt for cold white.

The light engine incorporates a patented heat management system that combines a conventional extruded aluminium heat sink with a copper tube liquid heat pipe system. This is designed to carry heat away from the LEDs in a very efficient method and dissipate it into the atmosphere. Effective heat sinking is one of the key issues in LED luminaire design to achieve long life and good efficiency.

The heat sink seems to be of an adequate size for the power rating of the downlight but if it would be interesting to know if the predicted maximum LED junction temperatures and light output figures are still achieved if the downlights are installed into a shallow ceiling void with limited air movement and a high ambient temperature.

The custom designed optics for the Evolution light engine have been designed to be replaceable and a series of moulded lenses is available with four beam angles from 12 to 48 degress. Changing the optics was a bit fiddly on the sample I was given but since this would not normally be done more than once that should not be a major issue and it is understood that the final production version is easier to use.

ACDC claim that their Evolution light engine with 9 Luxeon Rebel LEDs running at 2 watts per LED gives an equivalent light output to a 50 watt halogen lamp. So I compared the light output of the test samples with various Wattages and beam angles of low voltage MR16 lamps.

The first impression of the Evolution is that the light output is high but when given a direct comparison test the centre beam intensity with the narrow beam optic seems to be around the same as 12V 35W medium flood MR16 lamp. It certainly does not have the concentrated lighting effect of a 10 degree 50 Watt MR16 which provides around twice the lighting levels in the centre beam.

The colour rendering of the warm white samples had the slightly pinky grey quality that LED manufacturers believe is close to halogen. It is not really comparable to halogen in terms of colour, colour rendition or sparkle but is definitely much better than the quality of warm white LEDs available only a couple of years ago.

The use of LEDs for downlighting in commercial applications is going to be a major market. If light quality is the key issue then LEDs are not quite there yet but are improving all the time.

At the moment it is not clear that the use of LEDs for general energy efficient downlighting makes commercial sense when compared to the alternatives of good quality compact fluorescent or miniature metal halide luminaires. However there are an increasing number of applications where these light sources may not be the best choice. If a small aperture size, dimming or lamp changing problems are important factors then using LED downlights could now make sense.

The combination of the ACDC light engine with the Lucent Lighting Prospex downlights makes an effective luminaire with some attractive features. This market segment is going to be highly competitive as every commercial lighting company will from now on start to offer LED light sources as an option in their downlight ranges. As an early entrant into the market with a well engineered product ACDC deserves to do well with the Evolution range.


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