The use of high resolution spatial and spectral mapping of blue LEDs may lead to curing the ails of their white cousins

If you watch the news and filter out all the EU drama, the Olympics, stories about the Queen and football, then you will likely be exposed to the on-going worries about energy. 

Lighting and illumination in its many forms are responsible for using around 20% of global electricity, so cutting this down will be a major boon in the drive for the reduction in energy consumption. 

Compact fluorescent bulbs are the current poster boys of low energy lighting, but they have their own detractors and issues. Namely, the mercury used in their production, the unpleasant ‘coolness’ of the light in low intensity settings and the fact that the efficiency is still not as low as a light source could go.

Currently, white LEDs are based on a blue LED topped with a phosphorescent material which glows yellow when hit with blue light. And, if you remember your colour mixing from physics at school you’ll know that, in additive colour, yellow and blue makes white. So blue LEDs are the key.

So what’s the problem? Well, unlike red LEDs, blue LEDs are made from a particular material that suffers from an, as yet, undiagnosed ailment. People in the know call by the imaginative name of efficiency droop, for the unsurprising reason that the efficiency, they key advantage of the LEDs, drops off at high currents.

The group at Strathclyde have devised a new method for imaging LEDs which they hope will lead to answers for this power. Termed Electroluminescence Hyperspectral Imaging the technique involves scanning a bare LED chip underneath a spectrometer. At every step in the scan the light from the small area currently under the spectrometer is collected and analysed. In this way, an image of the LED can be built up whereby; instead of just the light intensity being recorded the entire spectrum of light emission is mapped pixel by pixel.  By performing this procedure with the LED driven at higher and higher currents where the problems start to kick in, the aim is to see how the variations in emission spectra correlation with decreasing efficiency and maybe find a way to make LED lighting the present as well as the future.