How to tell if your flashlight uses PWM or not

[roadkill1109]

Whilst I am sure you are right about the consistent color part, how does PWM equates to longer battery life? I am afraid I am clueless when it comes to this. Could you please enlighten me a little? Thanks!

Yeah, i'd like to be enlightened by that factoid.

 

[roadkill1109]

The regular Quarks are current controlled, not PWM controlled, am i right/wrong?

correct, Quarks are current controlled, but not all of them have voltage cut offs, Quark Turbo X is such an example, it will drain your rechargeable batteries to zero (0v) voltage, rendering them useless as chargers will not charge zero voltage cells. My older Quark AA^2 is much kinder to rechargeable cells because it would turn off when the voltage is not sufficient to sustain the light but not drain it to zero even if you left the light on overnight. (it's happened before, forgot the light, found it dead the next day, battery still had voltage, good light!!)

 

[roadkill1109]

I can't remember for the life of me if it is the regular/tactical quarks or just the mini's or both. I'll have to check again when it's dark, because they use such high frequency PWM that it is very very hard to detect

my quarks are both current controlled. did they release lights with PWM?

 

[roadkill1109]

circuits that provide steady power to the led must resist some of that power to in order to dim it,
this creates some heat in the resistance circuit and eats power that otherwise could go to producing light

PWM reduces or eliminates dimming completely, so nearly all power goes to lighting.
PWM fools the eye into thinking it is steady light and can dim it easily just by keeping it off more often

hmm, but wouldn't current regulated lights be more efficient as it is not resisting the power of the battery, but regulating it so a fixed amount of power goes to the emitter for the desired lighting level? making the led rapidly oscillating on and off (pwm) wouldn't that eventually shorten the life of the led?

hmm, time to study the internals of our lights!

 

[roadkill1109]

A light whining is not an indication of PMW, it is the driver circuit boosting voltage.

PWM is where the light output is flashing in order to achieve a higher perceived brightness for a lower power output, or by cheaper lights often to achieve the lower levels rather than using proper current control.

Correct! The Quark buzzes when it's trying to regulate the output of the light when the cell is almost depleted. At first i thought my Quark was busted! Now I know that when it starts to buzz, i should be careful coz my light's running outta juice.

 

[roadkill1109]

I asked marshall about the PWM, and he said its not that noticeable so I guess I will try this XT11. I just love the Klarus interface! Tactical lights rock! (Provided the Strobe and Flashy modes are conveniently hidden) Never know when you need to strobe an attacker (animal or human) in the eyes while out at night!

 

[127.0.0.1]

hmm, but wouldn't current regulated lights be more efficient as it is not resisting the power of the battery, but regulating it so a fixed amount of power goes to the emitter for the desired lighting level? making the led rapidly oscillating on and off (pwm) wouldn't that eventually shorten the life of the led?

hmm, time to study the internals of our lights!

it depends on how much money you put into the circuit and driver. PWM is cheap and reliable and allows near infinite control, and of
course easy strobe modes. I am going to back off on the efficiency part. there are many analog circuits driving LED that are more efficient than
PWM...so my factiod isn't really a 'blanket statement'

 

[Viking]

From flashlight-wiki:

PWM
Pulse Width Modulation. A technique of varying the brightness of a LED by flashing it on and off very quickly, making it appear to the eye that the LED is dimmer. Good PWM is at such a high rate that you can't notice it. But if you wave your hand in front of the light and get a strobe effect, the PWM is getting too low. Some use current regulation which makes the light dimmer without PWM and is also more efficient.

http://flashlight-wiki.com/Terminology#P

 

[calipsoii]

I am going to back off on the efficiency part. there are many analog circuits driving LED that are more efficient than
PWM...so my factiod isn't really a 'blanket statement'

Correct - a true "current controlled" light does not use resistors to dump excess current as heat. The current-controlled circuits I have constructed use a mosfet, a transistor and a couple sense resistors (which serve only to "tune" the output current).

A proper current controlled light will run much longer than a PWM-controlled one at the same output level - the difference can be upwards of 25%.

http://www.molalla.net/members/leeper/pwm_cc.htm

 

[pjandyho]

circuits that provide steady power to the led must resist some of that power to in order to dim it,
this creates some heat in the resistance circuit and eats power that otherwise could go to producing light

PWM reduces or eliminates dimming completely, so nearly all power goes to lighting.
PWM fools the eye into thinking it is steady light and can dim it easily just by keeping it off more often

Thanks. I figured it was so but I just wanted your confirmation.

 

[yifu]

The EASIEST way IMO is just get a digital camera from a phone or whatever and point it at the beamshot. If it flickers it's got PWM, if it doesnt then its current controlled.

 

[jh333233]

A light whining is not an indication of PMW, it is the driver circuit boosting voltage.

PWM is where the light output is flashing in order to achieve a higher perceived brightness for a lower power output, or by cheaper lights often to achieve the lower levels rather than using proper current control.

Whining could come from oscillation of inductors
Light whining can be one of the signs of PWM too
Oscillator on the circuit board generate the signal required for PWM and that is where the noise comes from

 

[roadkill1109]

Correct - a true "current controlled" light does not use resistors to dump excess current as heat. The current-controlled circuits I have constructed use a mosfet, a transistor and a couple sense resistors (which serve only to "tune" the output current).

A proper current controlled light will run much longer than a PWM-controlled one at the same output level - the difference can be upwards of 25%.

http://www.molalla.net/members/leeper/pwm_cc.htm

Wow! Great info, man! Learning a lot here!

 

[SaVaGe]

Another way is this. Its kind of funny but NOT. Shine your light infront of a fan in my case a very small square rotary fan on a heavy machinery at work. If it looks really slow it uses PWM. i was looking at the fan and i said...hmmm something is wrong with the fan cause its spinning slow and i stick my finger in it and i nearly lost it. And i said yep my light has PWM.

 

[Hondo]

i dont think that our household has a fan.
anyone with a youtube video demonstrating the fan vs. PWM trick?

You've already seen this, in almost any western film. As a wagon pulls up to a stop, the wheels will appear to be going in reverse, then stop, and finally roll forward as it slows to a stop. This is due the the period of the spokes moving from one position to the next in the wheel getting in and out of phase with the frame rate of the camera filming. Wagon wheel spokes are like fan blades, frame rate in the camera is like PWM at that frequency (pretty low in this case, like 60 Hz, I think). BTW, for this reason, trying to video the effect of "light vs fan" is not at all likely to come out well, the camera you will be using has a similar low frame rate that will be compounding with the light's PWM. You can get the effect with just the camera, no PWM light required.

Best way to do this is set the fan to it's highest speed, shine the light on it, then turn it off and watch as the blades are slowing.

 

[Hondo]

Another way is this. Its kind of funny but NOT. Shine your light infront of a fan in my case a very small square rotary fan on a heavy machinery at work. If it looks really slow it uses PWM. i was looking at the fan and i said...hmmm something is wrong with the fan cause its spinning slow and i stick my finger in it and i nearly lost it. And i said yep my light has PWM.

Zoinks! I knew PWM could be annoying, even sickening, but I had not thought of it as potentially dangerous, 'till now. This reminds me of some guys I knew that worked at a newspaper plant, and they have a lot of fast moving machinery. It moves so smooth, it looks stationary, but you don't want to be touching it. They would apply tape with intermitent sections of black and yellow on it, so that the parts would appear "flashing" as they went by, allerting all to the danger of the high-speed machinery.

 

[subwoofer]

i was looking at the fan and i said...hmmm something is wrong with the fan cause its spinning slow and i stick my finger in it and i nearly lost it. And i said yep my light has PWM.

There is a lesson in there....

 

[jh333233]

Some camera has the function of highspeed video shotting
Try to wave the light with that mode

 

[Animalmother]

The EASIEST way IMO is just get a digital camera from a phone or whatever and point it at the beamshot. If it flickers it's got PWM, if it doesnt then its current controlled.

I don't know much about PWM as i don't have not really noticed it any low fequency. Or becuase i don't buy lights PWM. I busted out my iphone 4s and shined it on bright at the wall. Didn't flickering as expected. But low mode looked like waves of lines glidin across the beam profile.

 

[2100]

A truly optimsed driver that does current control would run longer than a PWM light (doing the same light output of course).
I think i read something about the PWM freq, higher freq/switching might need more power than lower freq.

Anyway I can do 500Hz (Xtar S1 = 486Hz, Ultrafire U80 = 450Hz, On The Road X5 = 475Hz). I can use 207Hz (DRY triple XM-L) but it irritates me a bit, but it is definitely usable and tolerable in long durations. Below that is a no-no. Some budgetlights like the Uniquefire UF-2100/iTP are in the kHz region, the UF-2100 is doing 5kHz and my Shadow JM05 and JM07 are in the 4.5kHz range. You literally cannot see the PWM even in the shower (you could if you tried hard enough, but won't notice it in real life usage).

Another way is to put the light's front with black T-shirt or anything black and put your ears in front of it, you will hear the PWM freq very clearly up to your ear's limit (say 17kHz).

You can also use a DMM to measure it using the Hz function.