Lighting
from the operating lights, enabling alternative models from different manufacturers to be compared. Brandon Medical has submitted its latest Quasar eLite 60 and Quasar eLite 30 operating lights for testing to the new standard. The University of Giessen was selected to perform the tests, as personnel there carried out much of the pioneering work in developing the DIN1946 standard, and the university is accepted as the leading centre of expertise, with full-time testing facilities. The two-part test is undertaken with a single operating light head in a compliant UCV canopy. The first part is a test for thermal buoyancy from the operating light, to see if it creates an upstream air current in the reverse direction to the UCV supply- air direction. The test is carried out by positioning the operating lights in a carefully specified position as set out in DIN1946 (light head inclination: 45 degrees, light centre: 1.0 m below the UCV diffuser), and warming the lights up to operating temperature.
Use of a thermal camera The operating temperature is first established by using a thermal camera to find the hottest part of the light head, placing a thermocouple at the hot spot, and measuring the heating up characteristic of the operating lamp. The operating light has to be set to produce > 70,000 Lux at 1 m from the light while the thermal test is carried out. The Brandon Medical Quasar eLite was set at a slightly more stringent 90,000 Lux at 1 m, and thermal equilibrium was reached after around 60 minutes. Figures 1 and Figure 2 show the temperature probe positioning and thermal camera image. The test for lift (upstream air current) is
performed by introducing an aerosol fog 50 cms above the light head and then 150 cms below the light head. There is a visual check that none of the aerosol rises, which would be a test fail.
Degree of turbulence The second and main part of the test measures the degree of turbulence. As with the HTM tests for UCV ceilings, a grid is marked out on the floor under the UCV ceiling, but in 30 cm squares to determine the measuring points. Thermal anemometer probes are set up at the measuring points, 1.0 m above finished floor level, and 0. 8m below the centre point of the light head. Three sets of turbulence measurements are taken – the first without the light head to show the background level of turbulence from the UCV unit itself, the second set with the light in position (the same position as for the thermal buoyancy tests) but cold (turned off and cooled down to at least the temperature of the UCV air flow), and the third set of measurements is taken with
Figure 6: Parameters – Quasar eLite 30. Test Report
Average Standard Deviation
Coefficient of Variation Minimum Maximum
Boost 50 cms above Boost 150 cms below
Tu (%) 22 19 87 3
67
v(m/s) 0.2
0.04 20
0.11 0.27
No No
the light in position and at working temperature.
The results for the Brandon theatre lighting measured at Giessen are shown in Figures 3 and 4 for the Quasar eLite 60 and Figures 5 and 6 for the Quasar eLite 30. The figures for both lights show ‘no lift effect’ in the thermal buoyancy test, and easily meet the turbulence threshold of < 37.5%. Dr Siepp, Professor of Technical Building Equipment in Hospitals at the University of Applied Sciences in Giessen, commented that both models of light have ‘remarkably low operating temperatures’ of only 21.8˚C and 26.6˚C respectively, and that the Quasar eLite 30 in particular has the lowest turbulence of any light so far measured under the standard, at only 22% (with background UCV turbulence of 7%).The Quasar eLite 60 turbulence score was 31% (with background turbulence of 7%), which equalled the previous best of lights tested.
Conclusion
There are lots of different models of operating lights, all of which will cause at least some degree of turbulence in a UCV air flow. Some manufacturers, but not all, design their lights to minimise this turbulence to an acceptable level. There is now a practical test to measure the suitability of operating lights for UCV theatres, to quantify the turbulence they create, and to compare the products of
different manufacturers. DIN 1946 part 4 (12-2008) is the only test currently available to do this, and should be considered as setting out the key specification criteria when selecting operating lights for installation in ultraclean ventilation theatres. When selecting operating lights for UCVs, air flow turbulence is important, but it is not the only factor to consider. Lights in orthopaedic surgery get splashed with blood and body fluids, which have to been cleaned off between patients. There seems little point investing in ultraclean ventilation to reduce infection rates if lights cannot be cleaned effectively, and become an infection risk. The ease of cleaning and disinfecting of the lights should be considered carefully. The shape should be easy to wipe clean, there should be minimal split lines in the light head enclosure, and no exposed fasteners, nooks and crannies, hard-to-clean handles, or soft gaskets which allow contaminants to be pushed under the edges. Some operating lights include antimicrobial agents in the materials of the lightheads, which is an added bonus in disinfecting the lights, but not, however, an alternative to effective cleaning. The latest LED operating lights can be designed as single cupolas that still have excellent air flow suitability and are clean.
T-zu (°C) 20.4 0.16 1
20.2 20.9
✚
Graeme Hall
Graeme Hall is a Chartered Engineer, a Fellow of IHEEM, and a member of the IET. He has over 23 years’ experience in research, design, and development of operating theatre equipment, including LED operating lights, operating lights for UCV systems, medical pendants, and high colour rendition lighting. He is managing director of Brandon Medical.
Health Estate Journal 33September 2016
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