World's most accurate measurement of fundamental unit of light intensity achieved
17 Jul 2008, 1410 Hrs

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Canberra, July 17 (ANI): Australian scientists have said that they have achieved the world's most accurate measurement of the fundamental unit of light intensity.

According to a report by ABC News, Errol Atkinson and colleagues from the National Measurement Institute have refined the measurement of the candela, the basic unit of brightness, to eliminate all but 0.1% of uncertainty.

Atkinson told the 21st Congress of the International Commission for Optics held in Sydney, that they expect to have halved that uncertainty to 0.05% within months.

"To the best of our knowledge, the Australian realisation of the candela is currently the most precise of any international laboratory," he said. "We've already set a pretty good standard - and we'd like to keep it that way," he added.

The candela has been the Systeme International d'Unites (SI) unit of luminous intensity since 1946.

As its name suggests, it was originally defined as the amount of light emitted by a candle, but recently a more precise definition has been taken up.

The candela plays an important role in defining international lighting standards, and is used for a wide range of applications from household light bulbs, through to techniques to identify faults in the manufacture of jet engine components.

Scientists at the institute are also responsible for maintaining the Australian realization of the candela using a set of lamps in its Sydney laboratories.

They set the standard by measuring the light from a mercury-xenon lamp shone through a set of filters, and finally through a small 5 millimeter aperture in a piece of metal.

"These light sources have a very consistent light output," said Atkinson.

It was using them that allowed the institute to reduce the potential error in its standards to 0.1%. That uncertainty could be cut even further by taking into account tiny variations in the size of the aperture.

The scientists are currently working to do that by using an optical laser scanning technique to measure the size of the aperture more precisely.

According to Atkinson, because the amount of light coming out of a substance is also closely linked to its temperature, the advance could lead to a change in the way the SI standard for temperature is defined.

"That is a real possibility and could happen within the next couple of years," he said. (ANI)