# Why we can see electromagnetic wave with 50 Hz frequency???

Discussion in 'Wireless & RF Design' started by hona, Nov 13, 2014.

1. ### hona Thread Starter New Member

Nov 13, 2014
1
0
Hello all,
We know that visible light approximate frequency range is 400-700 Tera Hertz (THz). Human eye can see this spectrum of electromagnetic wave. AC power electricity have frequency of 50-60 Hz. therefore electric lamp light and the light that reflect from objects have 50-60 Hz frequency. thus why we can see such wave with low frequency???

2. ### alfacliff Well-Known Member

Dec 13, 2013
2,449
429
the light isnt radiating 50 hz emf, it radiates light. you can see a bit of 50 hz ficker on some lights tho.

Jul 18, 2013
12,885
3,521
I remember there was a case reported in the UK (50Hz) when the first fluorescent lights were installed in machine shops and wired on a single phase, the unseen flicker acted as a strobe light on machine spindles, so operators were in danger of losing fingers, as certain tooling appeared stationary to the operator.
This was cured by wiring the fluorescent in banks on each off 3 phases.
In an incandescent lamps the filament does not cool sufficiently at that frequency, some neon's you can just make it out.
Max.

strantor likes this.
4. ### strantor AAC Fanatic!

Oct 3, 2010
4,588
2,467
Very interesting, never heard that. Im sure you're familiar, but others might not be, and might find this interesting; there's a device called a stroboscope, which pulses light flashes at an adjustable frequency, to measure the speed of moving or rotating objects in the same manner. You adjust the pulse frequency until you see the object of interest "stop moving", and at that frequency you obtain the rotational speed (or some multiple of it). Similar to an automotive timing light.

5. ### Alec_t AAC Fanatic!

Sep 17, 2013
7,010
1,449
You cannot see 50Hz EM waves, but you can see 50Hz brightness modulation of EM waves.

6. ### shortbus AAC Fanatic!

Sep 30, 2009
4,513
2,549

It wasn't just 50Hz, the shop I started in as an apprentice was very old. The fluorescent light fixture were very old, certain speeds on the lathe looked like it was standing still. My last job, we some times used a stroboscope to see what was happening in the terminal make dies, they made terminals at ~1300 parts a minute. you could see problems in the die with the strobe.

strantor likes this.
7. ### mossman Member

Aug 26, 2010
131
3
To answer the OP's question, the light emitted by the bulb is in the visible spectrum (THz), which is why you can see it. 50 Hz is the frequency at which the light is turned on and off by the AC current flowing through it.

8. ### BR-549 Distinguished Member

Sep 22, 2013
2,997
724
As of right now, you can not see a 50 hz wave. If you could, it would have to be at great distance away. A 50 hz wave is 6 million meters long.

We can not directly generate frequencies in the 400 to 700 thz range. So what we do is heat a piece of wire.....white hot. The heat of the wire generate the light frequencies.
You can use DC or any frequency to heat the wire.

Strobe lights have been used for many. many years to image fast moving systems.