Malcolm Knight holds a banknote up to the window. As the light hits the paper, a shiny oval of blue lightbulbs on the face of the note suddenly disappears, revealing - as if by magic - a cluster of lighthouses. "It's very hard for a counterfeiter to rise to that challenge," he says.

Mr Knight is a former research and development director and now consultant at De La Rue, the discreet British banknote maker that has designed more than 40 per cent of the paper currency to have entered global circulation in the past two years.

Since 2008, it has worked on about 150 currencies either as printer, designer or provider of secure paper. It is trusted by central banks around the world for its security features that can shield a currency from forgers.

When South Sudan became the world's youngest country in 2011, it was De La Rue that got the call to provide the banknotes. It also designed and produced the first notes in post-Gaddafi Libya and hired 24 jumbo jets to supply Iraq after the fall of Saddam Hussein.

The disappearing lightbulbs might seem like a cute trick. But the technology lies at the heart of the battle to uphold the value of the world's paper currency against the evolving threat posed by "digifeiting" - forgery made possible by home technology.

It also forms the heart of De La Rue's mission to keep the banknote - a product that accounts for almost two-thirds of its revenues - relevant in a world of ecommerce, mobile payments and virtual currencies.

To read the complete article, see:The bold designs that deter banknote forgers(www.ft.com/intl/cms/s/2/b5939538-ae91-11e3-8e41-00144feab7de.html)