Recent comments in /f/todayilearned

RockItGuyDC t1_j7mnjkg wrote

I understand that it's not always possible for everyone, but this is exactly why I have zero electronics in my bedroom (aside from my phone charging on my bedside table, but that doesn't have an always on LED).

That plus blackout curtains have really improved my sleep!

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Ok-disaster2022 t1_j7mdka0 wrote

However there's an issue with emergency signage. Red is the color of danger, stop, while green is safe, go. Exit signs in areas of low literacy are green and green are becoming more common in the US to be more inclusive of people who can't read.

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planoavid t1_j7m6nu8 wrote

The lens and cornea of the human eye absorbs shorter wavelengths (blue) better than longer wavelengths (red) so less blue lights reach the retina.

The cones the retina uses to see longer wavelengths are active over a wider array of wavelengths vs the blue cone.

So it is easier for your eye to sense longer wavelengths of light than the blue light.

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Splice1138 t1_j7m56uj wrote

You might be a more extreme case, but human eyes can't focus on blue light as well, period. I know this first hand (and second, and third) from calibrating three tube RGB projectors back before LCD/DLP.

I also read about it being used in image compression. If you split an image into R, G, and B channels, you can save the B at half resolution and the difference is nearly imperceptible to human eyes, whereas it is easily seen if you do that with R or G.

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Jaksmack t1_j7m0gsb wrote

In 98 or 99, blue LED's we're still so expensive that I bought 1 to replace the green LED on my PC's power light. I was going to put them all over the PC case, but instead went with some cold cathode tubes.. the tubes and power supply was still cheaper than buying 1 LED. If I remember right, the LED's were like 25$ each..

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strangr_legnd_martyr t1_j7lzy1d wrote

Red LEDs do require less power. The forward voltage on a red LED is about 1.8V at 20mA. The forward voltage on a blue LED is about 3.6V. That's 36mW of power for red vs 72mW of power for blue.

Blue light has more energy than red light (higher frequency/shorter wavelength).

I think they generally favor red over blue for emergency systems, though, because red light has less effect on low-light vision. So if the power goes out, your red-lit emergency signs don't blind you in the dark.

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