[trhway]

>exposed laboratory mice that genetically predisposed to Alzheimer's disease to a light flickering at 40 hertz for one hour a day. They found that this treatment reduced the levels of tau and amyloid beta in visual cortex of the brain and stimulated the activity of debris-clearing immune cells.

does it mean that old CRT TVs and monitors kept our Alzheimer at bay?

[louthy]

I guess it depends how important the 40hz is. Because PAL was 50hz and NTSC was 60hz (if my addled memory is still working ok).

But it did occur to me that my years of going to raves, hearing (and feeling) sub-bass (in the 30-60hz range) could have a similar effect (especially when you throw in the strobe lights).

[rzzzt]

My old CRT monitor, an IBM 5154 clone, gave me a mild sunburn on the day I got it...

[mindslight]

Are you sure that wasn't just from having to go outside to buy it?

[dwighttk]

weren't fluorescent lights 40Hz?

[ridgeguy]

Older fluorescent lights (those run off a magnetic current limiter, or "ballast") flickered at 120Hz if they were connected to a 60Hz power source. Every time the voltage declined below a level needed to maintain a discharge, the lamp went out. That happened twice in every full sine wave of primary power.

Whether you could see the flicker depended on the phosphor luminous decay time. If the phosphors on the inside of the bulb (which glow when excited by the UV-rich plasma discharge) had a rapid luminous decay curve, you could perceive the 120Hz flicker if you scanned your eyes across a lit bulb. The afterimage on your retina was a dashed line, the dark parts being the "too little voltage" portions of the sine wave.

You can use the afterimage trick to check out duty cycle dimming of car tail and brake lights. If they're chopped slower than ~1KHz, the smeared retinal afterimage will be chopped. Don't do this if you're moving in traffic.

[vokep]

Yep! I do this in traffic when bored...not when moving tho, just sitting in stop and go traffic. Its interesting to see the different patterns, doesn't seem to be much consistency to the pulse width they have.

[ben_w]

I’d expect them to be an integer multiple of mains frequency, so 50 or 60 Hz.

[smaddox]

Flourescent lights need much higher frequency. They're typically >= 22 kHz.