Ten years ago lightpipes were unheard of in the UK but who would have thought that in eight short years, lightpipes, also known as tubular skylights or SunPipes would have had such an impact on architects and designers when considering the refurbishment of existing buildings and the development of new ones?

Lightpipes, the mirror-finish aluminium tubes,that can twist and turn carrying sunlight and daylight from the rooftop down to the ceiling below, were invented and patented by an Englishman, Stephen Sutton, nearly 17 years ago in Australia and the technology then moved to the USA. There are now more than 10 companies all manufacturing variations on the original Sutton design.

Monodraught first started importing lightpipes from Canada in 1996 but quickly saw the potential for this energy free system of natural lighting and accordingly developed the range to 10 different sizes, ranging from 230mm to 2m diameter systems. Monodraught have filed more than eight patent applications for their new developments, including the Diamond Dome SunPipes and the Square SunPipes. Monodraught sales account for more than 90 percent of the lightpipes sold in the UK and indeed, they are now selling more than 25,000 systems per year.

Three basic types

There are three basic types of lightpipe, an anodised aluminium tube, which formed the basis of the original Monodraught range; an aluminium tube with a 3M multi-layer polymeric film bonded internally; and the aluminiumised flexible spiral wound tube, which is made in a similar way to a tumble dryer hose extract. The increasing interest in lightpipe technology from architects has led to fierce competition between the main manufacturers to find the most reflective material and thereby give the best performance. One leading manufacturer from the USA produces a product with the 3M multi-layer film which proved hard to beat but a drawback of their system in the past has been that the polymeric film is prone to delamination, particularly under humid conditions.

Monodraught, however, recognised the challenge and last year, launched their Super Silver SunPipe, which is an aluminium tube impregnated with pure silver and then stabilised with PVD (Physical Vapour Deposition) which gives colour fastness and a 25 year guarantee.

BRE tests

Recognising the importance of establishing a totally independent criteria for assessing lightpipe performance and the impact this may have on the future development of lightpipes for the industry, Monodraught commissioned the Building Research Establishment (BRE) to carry out tests under both simulated sun and overcast conditions. The tests were carried out during the autumn of 2004 by Dr Paul Littlefair, who has been the Principal Lighting Consultant of the Environmental Division for the last 13 years and is recognised as the UK’s leading expert on daylight design. Firstly, Monodraught were pleased to see that the improvement measured under these tests between their original anodised aluminium SunPipe and the new Super Silver SunPipe was a 68 percent increase on the 300mm diameter SunPipe, which is the most popular system. The tests also showed that the SunPipe was 23 percent better than its nearest rival under overcast conditions. A summary of the report is shown here but full copies of the BRE Report can be obtained from Monodraught Limited free of charge.

The flexible tube was the least effective,with just eight percent transmission efficiency with the flexible tube stretched tight in a vertical situation.If the tube were angled to go around a bend,the efficiency would probably be less.

These tests,therefore,do give a great pointer for the future, since multiple elbows were also included in the test and tests were also carried out to measure the transmittance when lightpipes are applied horizontally.One test was carried out with a 2m long lightpipe with 90° elbows at either end.

Lighting tests

Future tests are scheduled to be carried out to assess the thermal properties of lightpipes and to also test the fundamental claim of all lightpipe manufacturers that there is no heat loss in winter months and no heat gain in summer months. Monodraught currently work with four different Universities to assess the performance of their products and whereas the academics accept that 99 percent of UV penetration is absorbed by the polycarbonate or acrylic domes,they insist that there must still be some IR penetration,although lightpipe manufacturers point out that this is partially absorbed by the external dome but also IR must be absorbed by the aluminium pipe itself on each ‘bounce’ of the light refracted through the tube.

On longer tube lengths of more than 2m,there may be as many as 14 or 16 bounces’of the light as it passes down the tube and, therefore, any IR that reaches the ceiling diffuser is negligible.

Nevertheless, it is important for the development of lightpipes that this technical argument is ‘bottomed out’ to ensure the continued confidence of specifiers.

Monodraught SunPipes have a 98 percent reflectance. That is as near to perfection as anyone is going to get! However,that means that there is 0.2 percent loss on every ‘bounce’, so the longer the lightpipe, the greater the loss is and in addition, there are, of course, losses through the roof dome or light collector and the ceiling diffuser. Nevertheless,the performance of a lightpipe is really quite remarkable and typically, the 300mm diameter lightpipe can light up a room of 10m sq to a normal daylight level, that is, without the need for electric lighting during normal daylight hours.

Larger lightpipes,of 450mm and 530mm diameter,are used in larger offices and buildings with higher ceilings, but for sports halls, dining halls, leisure centres ,etc, the 750mm and 1000mm diameter lightpipes are proving the most valuable.

Indeed, in Dubai, Monodraught are currently negotiating a contract to supply 750mm diameter SunPipes to all five exhibition halls at the Dubai World Trade Centre, to save the cost of electric lighting, which is otherwise required throughout the day during exhibition periods.This particular contract is just typical of many such projects throughout the world where a good level of lighting is required throughout the day and yet, even in those countries with maximum sunlight, electric lighting has to be used extensively in internal areas.

Energy savings

Monodraught is currently sponsoring a three year Lectureship at Nottingham University, designed specifically to look at the environmental benefits of daylighting through lightpipes and more specifically to assess the energy savings that can be achieved.

These energy savings are quantifiable and directly related to the building’s use.In schools, for instance, government sources say that 70 percent of electricity is used for electric lighting, since Schools are used mainly during daytime, it follows that the introduction of lightpipes to the rear of classrooms but also to corridors, toilets, store rooms and offices, will result in substantial energy savings.

A comprehensive schedule of energy savings will be produced by this three year study but in general terms, where lightpipes are used instead of traditional fluorescent lighting, a payback period of six years can be established.

The environmental benefits will also be studied at Nottingham University to determine the improvements in health benefits,the greater production rates that can be achieved, and the general improvement in human awareness and relaxation that can be achieved with lightpipes.Studies carried out in the USA by Heschong Mahone’s Consulting Group found that in a 1999 study on three schools with a total of 21,000 students,students with the most daylighting in their classrooms progressed 20 percent faster on maths tests and 26 percent faster on reading tests over the course of the year. These results were confirmed in a further study carried out in the year 2000.

The future for lightpipes

So what of the future? The great challenge for the lightpipe industry is to produce 24 hour energy free lighting by using small solar panels during the daytime to charge up solar batteries, which in turn will automatically provide power to LEDs, which will be embedded into the surround of a lightpipe diffuser, so that as external light levels drop, the batteries will fire up the LEDs internally. PIRs will be used in connection with this lighting arrangement, so that the lighting will only be activated when there is movement below but the impact for this energy free lighting arrangement will be enormous,not just for the UK but also for third world countries and indeed,developed countries throughout the world.

Monodraught is at the forefront of this development and is sponsoring this research, which is being carried out by Professor Mike Wilson of the London Metropolitan University to develop such a system and prototypes have already been made.Much depends on the current development of the more powerful LEDs that will be the key to the success of this new development. All the technology is in place, it is just timing now for the larger output LEDs.

Indeed, this PV technology is already used with Monodraught’s patented Sola-Vent,which uses a small 600mm x 300mm roof mounted solar panel, which charges internal solar batteries and the solar batteries in turn supply power to a 100mm diameter extract fan, which is integral with a SunPipe system.

Again,a PIR within the bathroom triggers the extract fan to provide 24 hour bathroom extract ventilation. With 98 percent reflectivity available with lightpipes, architects and specifiers are making greater use of the technology for bespoke systems.

Typical applications are hexagonal and octagonal lightpipe systems, which can be used for offices, reception areas, etc, that can even be fitted with coloured glass or special effect glass diffusers.

The worldwide demand for a reduction in fossil fuelled electric power and the demand for a dramatic improvement in sustainable engineering is well served by the lightpipe industry.

With eight years’ experience in the UK,Monodraught SunPipes have been proved to provide a dependable, predictable, energy free system, which has the added bonus of providing so many health and environmental benefits. Lightpipes may have come a long way over the years but the message is that they are definitely here to stay.

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