ITP A3 EOS Upgraded question

[RoBeacon]

When I was shining around in a computer case I noticed the medium and low setting give the fans the appearance of running slower than they are. Why is that? What is that called ? Do a lot of LED lights do that?

 

[kyhunter1]

I think it's called PWM. PWM switches the light on and off really fast at mostly unnoticeable speeds to reserve power and give lower modes in some lights.

 

[kramer5150]

Pulse Width Modulation. Its how the microprocessor dims the output, by flashing the LED on/off at a higher frequency than the human eye can detect. It becomes visible when shining the light at fast moving objects, like how a timing light is used to measure engine RPM.

 

[RoBeacon]

Good to know thank you. Do companies usually give the specs out of the frequency for the pwm?

 

[HKJ]

Good to know thank you. Do companies usually give the specs out of the frequency for the pwm?

Only a few companies does that, but we are some that measure and publish them.

 

[PerttiK]

Point the light up and wave it back and forth, you'll see the pwm, quite many lights have that on low settings.
Here's a picture with itp a3 on top and quark mini aa on bottom.

 

[jk037]

The timing light as mentioned above is an excellent analogy. You'd see a similar effect if you were watching somebody dancing under a rapidly-flashing strobe light.

With PWM, the LED is switched on at full current (and hence full power), then switched off again; this happens several hundred or thousand times per second. The ratio of the length of "on" time to "off" time in each cycle determines the average power output. More info below:

http://en.wikipedia.org/wiki/Pulse-width_modulation

Depending how fast the switching frequency is, it can make moving objects appear to rotate slower, stop, or reverse.

http://en.wikipedia.org/wiki/Stroboscopic_effect

 

[Wiggle]

On that note, we did a lab at school once and we'd use a stroboscope to measure the RPMs of a spinning shaft. And in our lab manual it said "Even though the shaft may appear motionless when the stroboscope is on, DO NOT place your hands on the rotating shaft". Haha, I'd like to meet the guy who actually thought the stroboscope "froze" the shaft in place and it was now safe to handle Well actually not, he probably has a mangled hand...

 

[Dan FO]

On that note, we did a lab at school once and we'd use a stroboscope to measure the RPMs of a spinning shaft.

It's RPM (Revolutions Per Minute), not RPMs. RPMs would be Revolutions Per Minutes. :naughty: Then the question would be, how many minutes?:shrug: