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A (LED) lightbulb moment

Marshalls plc ammonite logo
Tuesday 27th February, 2018

Notebook of Coda Lantern

The development of the CODA lantern.

Light Emitting Diodes or LEDs have revolutionised the lighting industry. If you go to a lighting show now, finding a luminaire based around a traditional lamp is like looking for a needle in a haystack. It is rare for a technology to dominate an industry so completely. However this new technology took a bit of time to develop and evolve.

When white LEDs with outputs suitable for general illumination first became available, some manufacturers rushed products to market. The technology was not completely understood and a lot of mistakes were made. Many unjustifiable claims were made as to LED output and life, and often LEDS were packaged into existing or unsuitable luminaires.

I took a different view on the technology – I decided to step back and wait a while before bringing a product to market. I spent some 18 months learning about LEDs, visiting various suppliers and attending various technical seminars to learn about them in more depth. I also attended an extrusion design course run by a major manufacturer and visited companies specialising in low cost injection moulding and lenses for LEDs.

CODA lantern

One of the fundamental concepts, that is often misunderstood, is that LED light output depends upon the temperature they operate at, commonly known as the junction temperature. This temperature also affects the operating life and the colour stability of LEDs. For example, most LED suppliers provide data sheets with the LEDs which give an output figure in Lumens. This figure is based upon the LED being flash tested at 20 degrees centigrade and not the temperature at which they would normally operate. Figures and graphs are available for the thermal derating of the LEDS at higher temperatures. The optical losses in the lens also need to be considered, as do the losses in the power supplies which power the LEDs. More than one manufacturer was guilty of initially publishing the Lumen output and Lumens per Watt figure for the bare LED, rather than what was actually achieved in the luminaire itself.

Over this time I amassed a lot of information on the requirements for LEDs, however a conventional mind set still predominated as to how to build a luminaire. It was down to a moment early one morning when all my thoughts came together regarding a new design. Not quite a eureka moment, but something close. Now whether it was the couple of glasses of red wine the night before or indeed the Tarantino DVD I had been watching I don’t know, but I sketched up a new design concept on a piece of paper at three o’ clock in the morning before going back to sleep.

The whole project was drawn up and quotes obtained before it was presented to the company directors as an alternative to an existing design being worked on. It was immediately adopted and taken on board as part of a new product range.

CODA luminaire

The idea was to use an aluminium extrusion as a heatsink, nothing new there I hear you say, but rather than have big fins as heatsinks on the top, put the fins out either side with much smaller ripples to increase the surface area and disperse the heat. The big advantage of this is that there are no fins to clog up with dirt, leaves, berries or worse, and that the extrusion can be used as the body of the luminaire to give it form as well as function, and to carry the power supplies etc. This wide flat form tapering to a nominal sharp edge bearing a strong resemblance to the Samurai sword Uma Thurman had been using to such devastating effect the night before. Needless to say the whole luminaire was nicknamed Samurai…

Using an extrusion gives the benefit of making the luminaire extendable and capable of carrying multiple LED modules. These modules were designed as sealed units which can be easily attached detached from the extrusion. The gear housing was designed as a casting and styled with the help of a design studio to keep the sleek lines of the extrusion. The Samurai name was (sadly) not available to us, so the lantern became part of the CODA range.

This is a good example of how knowledge built up over a period of time can suddenly come together and gel into a new design. The combination of extrusion design research, knowledge of heatsinking, and understanding of LED operating characteristics all came together in a design which is currently Patent Pending and was commended in the Lux Awards 2013.

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