The funny part is that blue LEDs were historically the hardest to make. Engineers tried for years, but the shorter blue wavelength was elusive. But one Japanese dude managed to figure it out, and they exploded in popularity because they were the new futuristic thing. And now they’re actually one of the cheapest colors available, because every single manufacturer was rushing to jump on the bandwagon and has the equipment to make them. Sort of like the flatscreen TV crash in the early 2010’s, when TV prices suddenly crashed because every manufacturer was getting better and better at making the (historically very expensive) screen panels cheaply.

And to answer the question on why they’re so fucking bright, it’s because blue is a very short wavelength. It takes less power to produce shorter wavelengths. When you compare the relative brightness of two different colored LEDs, shorter wavelengths will be brighter. Like if you send 1 watt of power into two different LEDs, a blue LED will always be brighter than a red one (if everything else about them is the same). That’s why so many of the cheap RGB LED lights tend to be sort of blueish when they’re set to “white”. The “white” is just all of the individual diodes at 100% brightness, which means the blue tends to beat out the other colors.

But the engineers who design those things don’t stop to consider that a blue LED needs less power. They’re just checking the “has a power light” item off of their design punch list. They could undervolt the diode to make it dimmer, but that requires extra circuitry. Just get a diode that works on the same voltage as what you’re already using (probably 5v or 12v for a wall charger) and hook it up to the same voltage that you already have. And use a blue one because they’re the cheapest option. Congrats, you’ve just designed a charger that has a fucking blinding blue LED. The whole “people will want to use this in their bedroom in the dark” thing was never even a consideration.

This is also why red (and infrared) light is better at heating things up. Longer wavelengths carry more energy, which means they heat things up more when they come into contact. The wave takes more power to make, which means it is able to carry more energy to whatever you’re trying to make. Trying to design a blue heat lamp would be an exercise in frustration, because you’d be fighting physics. It’s also why the sky is blue during the day but sunsets are red. The blue light tends to get scattered by air molecules, (which is why the sky looks blue) but red light is able to punch through and reach the surface when the sun is at a steep angle (like during a sunset).