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Sill WindowLighter

Issue 59 Feb / Mar 2011

While trawling the aisles of The ARC Show, David Morgan finds a niche product with remarkable performance and a proud pedigree... the Sill WindowLighter.

Making its UK debut at The ARC Show was the WindowLighter from Sill Lighting – the company known for the quality, efficiency and sophistication of its technical lighting products and especially its exterior floodlights and projectors.

This luminaire is designed to undertake one specific lighting task which, as the name implies, is to illuminate the exterior window reveals of multi-storey buildings without spilling stray light either into the building or out to the sky.

This new luminaire design has emerged from a cooperation between Sill and one of Germany’s top lighting design practices to create a low-profile, aesthetically neutral fitting to sit discreetly on a window sill - capable of edge-to-edge lighting of the window reveal.
The WindowLighter sits on the window sill and projects light out in an arc of around 200 degrees with a very narrow beam of around 5 degrees. The output from the optical system pushes light away from the building at around 15 degrees but as the mounting bracket is adjustable and lockable this angle can be controlled to achieve the desired effect as required. The mounting bracket and cable entries are located away from the window side of the luminaire so the view from the building is very minimal. This very shallow luminaire is only 100mm deep and is designed to cause as little disturbance to the view or create any glare when viewed from within the building.

The WindowLighter can also be used for façade lighting where the luminaire is reversed so that the beam is directed back towards the building and is mounted on an extended bracket.
The original concept for the WindowLighter came from the well-known lighting designers Licht Kunst Licht in Berlin and the development was then handled in-house at Sill by the technical director Mr. Feldmann. Already, two projects have been completed with this product in France and Switzerland.

Sill has been in business since 1954 and, as one would expect with a company of such repute and longevity in the sector, the design and engineering of the WindowLighter is well done. Since this is a niche product for a rather specific application and is therefore unlikely to sell in high volumes, Sill appears to have sensibly used good quality off-the-shelf components and low tooling cost processes to launch the product.

To create the 200° distribution each of the 9 x 3W LEDs is mounted at a different angle onto the cast enclosure. Each of the Luxeon Rebel LEDs is mounted on aluminium star pcbs to the generous cast heat sink bosses. In normal operation in a 25 degree ambient the housing runs very cool and, although the passive cooling system is rated for use up to 35°C, this is likely to be a very conservative rating given the power and overall surface area of the luminaire. Sill has kept to a minimum any unnecessary surface ‘heat sink’ ribbing that gives a clean and unfussy appearance. The generous surface area and dark colour of the luminaire is sufficient to dissipate the heat from the LEDs and drivers. There is no active thermal control system to cope with very high ambient temperature situations but given the low running temperature this does not appear to be an issue.

A combination of elliptical and symmetrical TIR lenses with different beam shapes control the initial light output from the LEDs. The light then passes through a three panel secondary ribbed glass lens which is bonded into the cast cover blending the light pattern together to create a homogenous blade of light.

Twin OSRAM 18 watt drivers are used to drive the nine LEDs. We measured the power consumption for the luminaire at around 27 watts but do not have any figures for light output. The two layers of lensing used to create the light distribution probably reduce the efficiency of this product to a lower level than a simple wall wash luminaire. Dimming is achieved with a variable resistor in each luminaire. This simplifies wiring and control and allows the light output to be precisely tuned for the position in the building. In older buildings where window reveals tend to be shallower towards the higher storeys, a further advantage is that the light output can be adjusted to equalise the lit effect for the whole building.

Apart from a very slight striated output from the ribbed glass the light control is very effective. The tight cut off from the optical system means that almost no stray light enters the building and the occupants will experience little glare.

Although fixed colour versions are available there are no plans at the moment to offer a colour changing option. Suitable colour mixing lenses for the four colour arrays such as the Cree MCE are much deeper than the simple TIR lenses used with the WindowLighter so the housing would need be much deeper to accommodate these.

The wiring is well-handled with two cable entries for looping in and out. The gland entries are at a low level so that the wiring can run unobtrusively along the front of the window sill.

The WindowLighter is a soundly-engineered LED luminaire and is likely to perform well with many years of usage.

David Morgan runs David Morgan Associates, a London-based international design consultancy specialising in luminaire design and development.
Tel: +44 20 8340 4009
© David Morgan Associates 2011

The views expressed in this article are entirely those of David Morgan and not necessarily those of mondo*arc.


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