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arrangement and that means that we are not only experimenting with the number of fixtures but with light levels as well. SS: So you are already using less than the original design of 150 lux that I initially did when the programme first started? SV: Yes we are. The original design had more fittings per room than what we installed. I’m really happy with the energy efficiency – that is the main driver for me. Obviously the other driver is the quality of light. DC: There’s another driver though and that’s for the conservators and scientists. The fact that we can run at a lower lux level means that less energy is hitting the works of art. I understand that measuring lux is a crude device but it’s still useful. SS: You have a certain amount of lux hours for all of your pictures? SV: We have a limit of about 12 kilolux hours per picture. SS: So if you can run lower lux levels it means you can display the pictures for longer. DC: In crude terms, yes. It’s interesting though because if I walked into the spaces and you asked me to guess the lux level I
would guess that they are much more. SS: Yes, they feel brighter, don’t they? DC: Yes, there’s something about the qual- ity of the light, the crispness. The peak in the blue was a concern for our scientific de- partment but if you look at all the benefits they are very excited about this as well. Plus there’s the ten-year life expectancy... SV: I’ve worked it out at between ten and twelve years based on about 3,800 hours a year. DC: For us, in addition to the quality of the light that we know will get even better, the part we love the most is the control factor. In particular, the basic physics of LEDs that lets them be dimmed without changing the colour temperature. That fits in with what we’re trying to do in conjunction with using
LED AND EFFICIENCY The improvement in the efficiency of the new spotlight lighting over and against the previous offerings can be measured by the attained illuminance per watt. The National Gallery previously illuminated the artworks using Eclipse spotlights for 100W low-volt- age halogen lamps all fitted with flood reflectors. Due to the low luminous efficacy of 22lm/W, the original accent lighting performed at 5lx/W. Yet, for an almost identical beam angle, the new Optec LED spotlights with Spherolit lenses achieve an efficiency of 23lx/W. This almost five-fold increase arises as a result of both the higher luminous efficacy of the warm white LEDs at 62lm/W and the high-performance of Spherolit technology. All this is without even considering the UV filter, which is necessary with low-voltage halogen lamps to protect the exhibits but which impairs the efficiency by an additional 8% due to transmission losses.
COLOUR RENDITION AND PHOTO SPECTRUM Colour rendition and preservation aspects are of crucial importance when illuminating paintings. Since warm white LEDs have a higher colour rendition index than daylight white LEDs (Ra85 and Ra70 respectively), warm white LEDs are therefore preferred for colour-sensitive applications such as in museums and art galleries. To avoid lighting-related damage, such as fading or drying out etc, three factors have to be considered: the photo spectrum, the illuminance on the object and the dura- tion of irradiation. To assess various light sources, both on their own and in combina- tion with protection filters, a parameter known as the “relative damage factor” is used. This indicates the ratio of the damag- ing radiation intensity and the illuminance. Short-wave components of light are more harmful because they have higher energy levels. The higher blue component in the photo spectrum of daylight white LEDs makes them unsuitable for sensitive exhib- its. Warm white LEDs, on the other hand, have a relative damage factor that is even lower than that of the previous standard of low-voltage halogen lamps with UV filter.
DEUTSCH DEUTSCH
Zwei traditionsreiche Londoner Top-Institutionen, die Na- tional Gallery am Trafalgar Square und die benachbarte National Portrait Gallery, richten ihren Blick in die Zukunft und rüsten ihre Galerien nach und mit LED Beleuchtung um. Die durch Experten im Laufe ihrer Ermittlungen und durch LED Technologie-Produktmuster in beiden Galerien gesa- mmelten Ergebnisse führten letztendlich zu der Entsche- idung, ERCOs LED Beleuchtungstools festzulegen und interessieren auch stark andere Museen und Galerien. Die Messlatte für die LED Beleuchtungsqualität lag bere- its sehr hoch, da die bestehenden Systeme hauptsächlich von ERCO stammten und bei ihrer Planung hochmodern waren. Sie umfassten computerkontrollierte Steuerung von Tages- und künstlichem Licht, plus Spotlights für Niederspannungs-Halogenlampen mit UV-Filtern und bisweilen mit Farbkorrekturfiltern für warmtoniges Licht von mit dem Tageslicht abgestimmten Glühlampen. In
Bezug auf das Energieeinsparungspotential sind die Zahlen der National Portrait Gallery klar und präzise. Seit der Umstellung auf LEDs verbraucht die Beleuchtung der Galerien nun 68 % weniger Strom und das ohne Berück- sichtigung der Einsparungen durch reduzierte Wärmeb- elastung für die Klimaanlage.
ITALIANO
Due delle maggiori e più tradizionali istituzioni lon- dinesi, la National Gallery a Trafalgar Square e la vicina National Portrait Gallery hanno fatto dei passi avanti verso il futuro convertendo tutta la loro illuminazione in un’illuminazione al LED. Dopo aver valutato campioni di tecnologie al LED in en- trambe le gallerie, gli esperti hanno optato per la scelta di dispositivi della ERCO, di elevatissimo interesse anche per altri musei e gallerie. Gli strumenti di misurazione della qualità d’illuminazione al LED erano già preesis- tenti in quanto il sistema d’illuminazione precedente era stato fornito dalla stessa ERCO ed era, al tempo della
progettazione, fatto ad hoc. Il sistema include un sistema automatizzato di regolazione della luce naturale ed artifi- ciale, più punti luce per lampade alogene a basso voltag- gio incluse di filtri UV e di correzione del colore al fine di allineare la luce calda delle lampade incandescenti alla luce naturale del giorno. In termini di risparmio energet- ico, le cifre riportate dalla National Portrait Gallery sono chiare e concise. Dalla conversione al LED, le gallerie ora consumano un 68% in meno di elettricità, senza peraltro considerare il risparmio ottenuto da un ridotto carico ter- mico a vantaggio del condizionatore d’aria.
ESPAÑOL
Dos de las instituciones de Londres con más riqueza en tradición, The National Gallery (La Galería Nacional) en Trafalgar Square y muy cerca de ésta, The National Portrait Gallery (La Galería Nacional de Retratos), se en- cuentran mirando hacia el futuro y están convirtiendo a sus galerías, una a una, con luces LED. Los hallazgos reunidos por los expertos en ambas
galerías durante sus investigaciones y el muestreo de productos de tecnología LED, que en última instancia condujo a la decisión por las herramientas de iluminación LED de ERCO, son de gran interés para otros museos y galerías de arte. El listón con que se medía la calidad de la iluminación LED ya se había fijado muy alto dado que los sistemas existentes pertenecían principalmente a ERCO y, al momento de su planificación, eran lo último en tecnología. Incluían la regulación de la luz de día y la luz artificial controlada por computadora, más luz direccio- nal para lámparas halógenas de bajo voltaje equipadas con filtros UV y ocasionalmente con filtros de corrección de color para brindar la luz de tono cálido de las lámparas incandescentes en línea con la luz del día. En términos del potencial de ahorro de energía, las figuras que re- surgen de The National Portrait Gallery son muy nítidas y concisas. Desde que se cambió a los LEDs, la iluminación de las galerías ahora consumen un 68% menos de elec- tricidad y eso sin contar los ahorros llevados a cabo por una carga térmica reducida en el aire acondicionado.
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