Take a closer look at almost any functional appliance and you're bound to see a light-emitting diode (LED) or two, quietly glowing to indicate a function is working or that power is still   being consumed somehow. They've been around for roughly forty years or so but their future looks even brighter ... they're predicted to be the super cheap light source of the future, using much less power than regular light sources and lasting for around ten to thirty years each. Now that's brilliant. DP

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