I think that we don’t always realise the impact that General Purpose Technologies (GPT) have had in our lives.
My definition of GPT is when things become so widespread that we see their applications all around us then they are General Purpose Technologies. In addition, my other criteria is when the economies of scale have brought their prices down to such an extent that these technologies become ubiquitous.
The following picture describes four such GPTs, can you guess what that are?

So these are: solar panels, lithium batteries, passive infrared sensors and light emitting diode (LED) lights.
Their combined use, in this particular application, means that this could be installed by anybody as it is completely safe – a low voltage system. Thus no expensive electrician required to do the installation, no 230V(EU/AUS)/120V(US) cabling and no certificate of compliance (CoC) from that same expensive electrician. The older halogen mains connected system would cost hundreds of dollars to buy all the components and get the licensed electrician to do the installation and then certify it as safe! The system shown here would cost less than $50 from a local hardware store and you could install it in less than 10 minutes without running foul of the electrical codes. The bonus of course is that it will still work during a power failure owing to the battery which is charged by the solar photo-voltaic panel so completely sustainable and renewable…
I love LEDs because their power consumption is very low and they are so safe, most of the individual units run on anything from 1.5V to 5V. We all love light and color which LEDs are exceptionally good at producing.
I was astonished how cheap these have become, these tealights would replace the dangerous open flame, candle-based units and last for many years. They also create a lovely ambience no matter what the occasion, even the occasional power failure (outage). These cost me less than 50 cents each within this 8 pack and even included the CR2032 batteries, viola! Date-night at home is going to be soo romantic due to this GPT :,-) Thanks to the engineer whom invented LEDs…

Thanks to Messrs Round (1907), Losev (1927), Biard (1961) and Holonyak (1962) and those that secured to increase their lumens output whilst driving their costs down. Thanks to engineers in companies like Toshiba etc we get amazing, commercially available LEDs, that have an efficiency of up to 223 lumens/watt.
The control of LEDs has also advanced and by mixing the intensity of red, green and blue, any color can be obtained from these three colour LED devices. Check out this rather inexpensive “Disco ball” which listens to the music and then responds with a fantastic display of color light.
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