The simple Diode and LED Tester presented here costs under £5 to build (including all components, the battery and a cheap case) and will indicate the polarity of almost all types ...

"Reducing blue light with a new type of LED that won't keep you up all night." ScienceDaily. ScienceDaily, 28 April 2021. <www.sciencedaily.com / releases / 2021 / 04 / 210428140852.htm>.

With LEDs, electric current passes through a semiconductor (or diode) to produce light that is brighter and often has a wider beam pattern than other types of headlights.