Bulb busting light source invented

Edison rotates in poorly-lit grave

Researchers working on organic light-emitting devices (OLEDs) have made a critical jump that could finally call lights out time for the humble bulb. Since OLEDs are transparent when switched off, the prospect is of whole surfaces like walls, windows, or even curtains flooding rooms with brilliant white light.

University of Southern California Professor Mark Thompson said: “This process will enable us to get 100 percent efficiency out of a single, broad spectrum light source.”

The American team's breakthrough was to make OLEDs able to emit the daylight-style white light needed in homes and offices. Previous efforts had had struggled to get the full spectrum of wavelengths required.

OLEDs are made of four ultrathin layers; one for each of the primary colours, and one that does the actual light emitting as excited electrons fall back to their original energy state.

The problem was with the blue phosphorescent layer, which wasn't as efficient as the other two and short-lived. Thompson's team switched the blue layer's phosphorescent chemical for a fluorescent one. The subtle difference in the speed of the electron's energy transitions between phosphorescence and fluorescence can be adjusted for, without losing energy.

OLEDs do not produce heat like a traditional incandescent filament bulb, and are even more efficient that current energy-saving fluorescent bulbs. In a current fluorescent bulb the colours are all produced in a single layer, which causes some of the light to be lost by electrons combining with each other rather than radiating light.

The only hurdle left for the technology, Thompson says is for the plastic coating to be improved so that water cannot degrade the OLED. They will only need replacing every five to ten years.

The invention has obvious tech applications. Companies are already looking into it for mobile screens, and flat panel displays.®

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