Explain how brightness levels work for me

I'm still a newbie as far as understanding how stuff like this works - way back in Grade 10 science, the circuitry diagrams were most confounding, so please bear that in mind when explaining.

From what I understand about flashlights and brightness, based on either different user selectable modes, or how much juice is left in the batteries, a user can adjust the light's output using:

a) Pulse Width Modulation, or
b)Uh, not Pulse Width Modulation - I forget what it's called

If I had the choice of two lights with adjustable modes, one by a) and one by b), I would choose b) - the non PWM light, because flickering (even that some other people may not notice) bothers me.

I just had an *extremely* quick look at how light dimmers work on Google. The simplest gist of it that I got is that voltage is applied to only half (or some fraction) of an AC cycle.

If a flashlight is Direct Current and there's no cycle to alternate and no way for the voltage from the batteries to be applied to a dip in the cycle, like with 60 Hz AC electricity, and the light (choice b)), isn't using PWM, how does it function on a lower than full power mode?
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Now, about dying batteries and dimming bulbs/emitters - I've read in the last few days about Surefire's idea of what "usable" lumens are, and the disappointment some people have to find that the advertised run-time of some lights is based on the output weakening with the battery.

The opposite of that is, if I understand, a light which uses a regulated circuit. Am I right so far?

How does a non-regulated (dimming light with weakening battery) versus a regulated (full power and then the battery cuts off) light compare to one another - that is, how do they function internally?
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I appreciate your help in understanding these great mysteries of flashlightdom.

Thanks!

R.ticle One

It's all done with electronic circuits. There, that was easy, right?

Pulse width modulation just involves turning the power on and off very fast. If you vary the ratio of on time to off time you can control how much power reaches the load. This can work with DC batteries because electronics are used to do the switching.

The alternative to pulse width modulation is just to put a resistance (like a throttle) in the circuit. This has the advantage of cheapness and simplicity, but it has various technical disadvantages so it typically is only used in cheaper, low power lights.

As for regulation, it is the same answer: electronic circuits. A non-regulated light just connects the battery to the bulb or LED, so the bulb gets dimmer when the battery voltage runs down. A regulated light has an electronic circuit that changes the battery voltage before it reaches the bulb and controls the voltage at the right value. With LED lights the circuit actually regulates the current rather than the voltage, but the effect is the same.

Thank you, Mr. Happy. Basically as I understood it, but worded more simply than I could have.

The thing to realize is different lights using a different frequency for PWM. Most use a frequency that is far above any human detectable level, even by the most sensitive people to it.

Mr Happy said:

It's all done with electronic circuits. There, that was easy, right?

Pulse width modulation just involves turning the power on and off very fast. If you vary the ratio of on time to off time you can control how much power reaches the load. This can work with DC batteries because electronics are used to do the switching.

The alternative to pulse width modulation is just to put a resistance (like a throttle) in the circuit. This has the advantage of cheapness and simplicity, but it has various technical disadvantages so it typically is only used in cheaper, low power lights.

As for regulation, it is the same answer: electronic circuits. A non-regulated light just connects the battery to the bulb or LED, so the bulb gets dimmer when the battery voltage runs down. A regulated light has an electronic circuit that changes the battery voltage before it reaches the bulb and controls the voltage at the right value. With LED lights the circuit actually regulates the current rather than the voltage, but the effect is the same.

Click to expand...

If I understand it correctly, the big disadvantage to using resistance(s) is that the same load is put on the battery as it is with max brightness. In other words, you aren't getting any more run time, you're just getting less light. I can imagine that's sometimes what one wants but if I have understood why most people want variable output modes, it's to increase the run time.

I expect some people need very low output if they are being creepy-crawly and trying not to be seen, and then variable modes could be very handy, maybe even essential.

Personally, I buy non-adjustable if I have the choice, and if I don't have the choice, I just use it on max anyway. If it's only possible to turn it off by cycling through reduced output modes, I don't buy it....... easy!

Marduke said:

The thing to realize is different lights using a different frequency for PWM. Most use a frequency that is far above any human detectable level, even by the most sensitive people to it.

Click to expand...

I hooked up my 3 mode P7 mag to the Oscope and found the PWM to be ~4Khz on low and med.. sound about right?

artec540 said:

If I understand it correctly, the big disadvantage to using resistance(s) is that the same load is put on the battery as it is with max brightness.

Click to expand...

Well no, the load is smaller with resistance in the circuit and the run time is longer. However, some power is still wasted. For instance, to run a bulb at half power the power consumption from the battery would still be 71% of full power. So 21% of the power is wasted.

A second problem is a lot of heat can be generated in the resistance, which needs to be safely removed so it does not damage components. PWM dimming generally does not generate very much wasted heat.

The current control can be done with a resistor, but on most better lights it is done directly with the voltage converter, i.e. no extra loss.

Most led flashlights has some sort of voltage converter, either buck (to reduce voltage) or boost (To increase voltage), this is needed because a led needs 3.7 volt for max output and very few battery configuration can deliver that from start to finish.