PWM - What is it, How does it work and how to detect it.

[Cataract]

LEDs are more efficiency current dimmed down to about 5% of maximum. Below that, you are better to drive them at 5% and PWM them. As well, your circuitry is likely to be more efficient this way too.

Semiman

Wow, nice short and sweet explanation, I did not know this myself... Thanks!
(BTW, I believe you meant "you are better to drive them at 5% from maximum and PWM them.[...]"

 

[hiuintahs]

Wow, nice short and sweet explanation, I did not know this myself... Thanks!
(BTW, I believe you meant "you are better to drive them at 5% from maximum and PWM them.[...]"

No..........5% of maximum......down near off. But I probably should let Semiman speak for himself.

From 5% up to 100% is current regulated. But below 5% you set the current at 5% such that a 100% PWM duty cycle you get 5% of the maximum current. Then as the duty cycle ratio drops, the average current does also. For example a 50% duty cycle would then give 2.5% output.

 

[jon_slider]

... From 5% up to 100% is current regulated. But below 5% you set the current at 5% such that a 100% PWM duty cycle you get 5% of the maximum current. Then as the duty cycle ratio drops, the average current does also. For example a 50% duty cycle would then give 2.5% output.

Thanks for the info!
That model fits the Prometheus Beta Copper pretty closely... a 25% duty cycle of 5% of 85 lumens, would give 1 Lumen of high CRI from the N219, Im even more tempted to buy one now 🙂.. you guys are costing me money, lol

 

[reppans]

Thanks guys, so from what I'm hearing above, if I were looking for the most efficient light (assume 100 lms Max), it would be current regulated between 5 and 100 lumens, and then for any mode below 5 lumens, it would be current regulated to 5 lumens, and then PWM driven below that.

This does make sense, as I find my current regulated lights have their highest efficiency (in terms of lumen-hours) around the middle 2/3rds of their output range (~250 lms-hrs/Eneloop) and they start falling off hard on low lows (<100 lm-hrs/Eneloop @ sub-lumen) and high highs.

The Malkoff MDC AA is not using the CR-to-5%-then-PWM thing though - this light is pure PWM (aside from max) light - medium is PWM and Gene has mentioned he does not have the technology to do CR. But it does make sense that a pure PWM light like this could yield ~200 lm-hrs at both medium (~11 lms) and also still on its sub-lumen mode (with the only diff. being duty cycle).

Think I have reconciled this my mind now.... thanks, and I appreciate the input.

 

[Cataract]

No..........5% of maximum......down near off. But I probably should let Semiman speak for himself.

From 5% up to 100% is current regulated. But below 5% you set the current at 5% such that a 100% PWM duty cycle you get 5% of the maximum current. Then as the duty cycle ratio drops, the average current does also. For example a 50% duty cycle would then give 2.5% output.

Ah, got it... makes more sense this way... it is hard to drive anything at a very low current without losing efficiency.

 

[Cataract]

Thanks guys, so from what I'm hearing above, if I were looking for the most efficient light (assume 100 lms Max), it would be current regulated between 5 and 100 lumens, and then for any mode below 5 lumens, it would be current regulated to 5 lumens, and then PWM driven below that.

This does make sense, as I find my current regulated lights have their highest efficiency (in terms of lumen-hours) around the middle 2/3rds of their output range (~250 lms-hrs/Eneloop) and they start falling off hard on low lows (<100 lm-hrs/Eneloop @ sub-lumen) and high highs.

The Malkoff MDC AA is not using the CR-to-5%-then-PWM thing though - this light is pure PWM (aside from max) light - medium is PWM and Gene has mentioned he does not have the technology to do CR. But it does make sense that a pure PWM light like this could yield ~200 lm-hrs at both medium (~11 lms) and also still on its sub-lumen mode (with the only diff. being duty cycle).

Think I have reconciled this my mind now.... thanks, and I appreciate the input.

Good luck finding a manufacturer crazy enough to come up with a light that combines CR and PWM, although I think I met someone who might be just crazy enough to venture that way while I was digging the tunnels around here. It definitely wouldn't be a 100 lumens max light, though...

 

[Hondo]

Henry is that crazy. My HDS Basic42 has no PWM until you get to the real low modes. Then if I look for it, it is clearly there. It seems he still uses something like this, but maybe more like the Quark "warble" effect, I can't tell. It is hard to say that there is any fluctuation on the new lights by eye, but one of reppans' photos in the HDS thread shows something on the sub-lumen mode like what I have in some Quarks, but much faster and maybe with less % variation in brightness.

 

[Cataract]

A well-made (high frequency) PWM circuit can be extremely hard to detect. I remember some older review from Selfbuilt that could only detect the PWM on the scope... something like 10Khz! God forbids I would remember which brand, though.

 

[jon_slider]

some info I found educational, though older than the current Rev 3 Maratac. If anyone has specific PWM frequency info for any of the lights being discussed in this thread, please share links to reviews and facts. Specific examples of lights with specific PWM specs would be very helpful imo.

http://forum.multitool.org/index.php?topic=15912.40;imode
"PWM is a way to offer lower output levels without having to reduce the current to the LED.

With the E01's circuit, the current can just be set to the desired drive level. With a Maratac or a Fenix LD01, the drive current is set for the max level, and PWM is employed for med and low levels to reduce the output. Basically, the LED is driven at the same current for the med and low levels, but since the LED isn't powered 100% of the time, output is reduced and runtime is increased. Other lights, such as the rest of the Fenix line, use a separate current driver circuit for each level offered. This is a more expensive, yet more power efficient way of offering multiple levels in one light. The price of the circuit is not the only consideration when the decision is made to include PWM or current regulation into the design of the light. Other considerations are space constraints (size of the circuit board), and how many levels are going to be offered. If many levels are offered, such as in the NiteCore D10, a PWM circuit will most likely be used."

 

[masterP]

no reply from Surefire or Foursevens, even after several emails asking about some of their products

only reply was from Fenix

the Foursevens Preon Penlight is current controlled, not PWM. that might be my next purchase. I like the style and no strobe, SOS, or beacon modes!!!


http://budgetlightforum.com/node/20822


http://www.candlepowerforums.com/vb...xAAA)-Review-RUNTIMES-BEAMSHOT-VIDEO-and-more!

 

[jon_slider]

the Foursevens Preon Penlight is current controlled, not PWM. that might be my next purchase.

post a review 🙂 The preon seems like a nice smooth package.

I have an aaa light with PWM, that uses the N219 High CRI Led. Im so blown away by the colors, Im shopping for a non PWM with N219. I found the L3 Illumination L08, its next on my list. After that Im hoping to get some CRI readings comparing the PWM N219, to the Current Controlled N219, to see if it is true that PWM gives higher CRI on low modes.

I strongly recommend you include color temperature in your considerations. Another non PWM N219 aaa is the EagleTac D25 AAA

 

[masterP]

thanks for all the info guys.....just bought a Preon Penlight for my father. no PWM


pictures upload

 

[scs]

To folks who are sensitive to PWM and/or experience discomfort from PWM, does the tint influence the severity of your sensitivity and/or discomfort?
Anybody here who still perceives and/or feels the presence and/or effects of PWM @ 2+ kHz?

 

[Cataract]

My few PWM lights are cool white so I can't say for sure, but I don't think I would be much less disturbed if they it had a neutral or warm LED in them. It might feel a tiny bit less aggressive for me IMO.

As for frequency I never gathered the exact frequency info for my lights so I don't really know either. The consensus in the past was that at 10KHz+ it should be absolutely undetectable, although a few have said that it was still unbearable for them. Some still prefer PWM lights as they say they hate the tint shift they perceive from current controlled lights on very low modes, but they mostly choose ones with a high enough frequency (IIRC something like 4kHz and up, depending on personal preference).

In the end, there is a very personal or subjective component to perception to PWM frequency and tint shift, but there is a majority of people who agree to certain limits. Hopefully some people will chime in and help you get a more definite answer to your question.

 

[Cataract]

thanks for all the info guys.....just bought a Preon Penlight for my father. no PWM

That's great!

 

[jon_slider]

http://www.flashlightreviews.ca/Preon.htm
"the Preons use pulse-width-modulation (PWM) for their Lo/Med modes."

Some single AAA drivers that I know of that use No PWM are, thrunite Ti3, Olight i3s, Fenix E05 2014, L3 Illumination L08, Prometheus Beta aluminum and nickel

Some single AAA drivers that I know use PWM include, Maratac Rev 3, Prometheus Betta Copper, Preon 1 and 2

Some single AAA drivers that use no PWM but have a sawtooth wave are DriverVN, and Eagle Tac D25aaa

 

[more_vampires]

A CPF'er was telling me that the only way to the non-PWM Maratac rev 2 was to driver swap as previous poster mentioned. At time of posting, only the rev3 drivers are available if you wanted that copper host body.

Hate it when a maker of an awesome host body adds a feature that some of us don't like...

That said, I'm sure plenty of people will go for the rev3. It's all in what you prefer.

 

[jon_slider]

A new way to detect PWM, use the spin cycle
see the 4minute 15second mark…

Quiz, why are there dots, instead of a constant streak of light?🙂

 

[Cataract]

I've washed many lights by accident, but I have never thought of putting one in on purpose while it was on! Maybe I should EDC my lights in my socks so they don't clank around the dryer like crazy... Good find though. Makes me wonder how fast my washer spins so I could calculate the maximum PWM frequency I could detect this way.

 

[JenniferMa]

very nice article,thank you.