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TECHNOLOGY / PRODUCT REVIEW
POLE POSITION?
David Morgan takes a look at the Polestar LED 2010 Ambient Dim™ by John Cullen, an LED downlighter that changes colour temperature to mimic the effect of a halogen or incandescent light source
The Polestar LED 2010 Ambient Dim downlight is targeted at the residential market and so is a great deal smaller than other products on the market. It gradually ‘warms up’ as it is dimmed. This enables it to mirror the quality of light produced by low voltage tungsten halogen. The chromaticity chart illustrates the Ambient Dim in action
John Cullen was founded in 1981 and provides a complete lighting design service as well as supplying a range of upmarket luminaires for residential and hospitality lighting applications.
Most of the luminaire range is designed in house by lighting design director Sally Storey with other members of the lighting design team and product designer Graham Lunn. The Polestar downlight range was originally designed for use with MR16 halogen lamps and is small to match the scale required for residential projects. With a bezel diameter of only 69mm and made of thin steel the downlight is very discrete. The black anti glare baffles gives a well controlled dark- light effect. With 30 degree aiming from the vertical it is designed for picture and feature lighting as well as general down- lighting. The Ambient Dim LED 2010 white light en-
gine is a new development that intriguingly changes colour temperature as the LED light engine dims in an attempt to mimic the warming effect of a dimmed halogen or incandescent light source. This is certainly an effect that is very desirable for any resi- dential low energy efficient lighting product as commercial LED downlights do not give a suitable ambience in these applications. Although the colour temperature chang- ing feature is not unique as there are now a number of retrofit lamps on the market which incorporate this effect the John Cullen system is certainly one of the first to be integrated into a residential scale downlight. Colour temperature changing retrofit LED lamps from Ledzworld from The Netherlands and Feelux from Korea are GLS or PAR sized and designed to fit into larger luminaires and table lamps. The LED light engine used in the Polestar LED 2010 Ambient Dim combines a central
warm white 1 watt LED with a surrounding ring of six cooler white 1 watt LEDs. The colour temperature shift effect works by keeping the warm white LED on full power while the cooler white LEDs are dimmed so as the amount of light from the cooler LEDs diminishes the overall effect becomes warmer until only the warm white LED is left on. A colour correction filter is also included in front of the standard collimating seven element lens and this enhances the warming effect still further.
The colour shift while dimming effect is not quite as smooth as dimming a halogen lamp as the driver for the cool white LEDs cuts out at around 5% instead of going down to zero so there is a step where the cooler LEDs suddenly cut off to leave the warm white LED on. However the overall lit effect is very pleasant and cosy when dimmed. Thermally the downlight seems to oper- ate within the limits of the Cree XPE LEDs
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