I’m really glad to have found this forum so I, as a newbie to current flashlight technology, can ask a few questions. I’ve asked a couple already, but I won’t make it a frequent habit.
For the last several weeks as I’ve looked for a replacement for my old Coleman LED, I’ve been fascinated by the high lumen output of some lights. I had fairly well decided I would get a Wowtac A1S, but then I shifted my attention to the Sofirn SP32A because of the side switch. But along the way I discovered the step down feature of such lights. With the Sofirn, you’re left with using the 160 lumen medium level for any extended us (unless you want to temporarily punch it up to a higher level). And that brings me to my question.
At about what lumen level do flashlights need to have a step down feature? I just bought a Coast Polysteel 250 at Walmart for the great price of $11.00 (it’s an odd duck; it isn’t on Coast’s website, and it’s only found in Walmart’s Fast Track collection, whatever that is). It’s supposed to put out 320 lumens on high using 3 AAAs. There’s no mention of it stepping down after a few minutes. So how high do lumens have to get before stepping down is necessary? (I hope this makes sense!) Few flashlights have stepping down in their descriptions on Amazon. It would help me to know this to zero in on a good lumen number when doing my search.
Everything has to do with the thermal path of the LEDs .., bigger the size of the head , better the cooling and the sustained lumens.
There is no direct connection between the amount of lumens and the step down , is about the necessity to protect the LED and the components of the driver against overheating.
The needs to have high lumens light ,in a very small package , are leading to the step down feature.., so, numbers are extremely relative , and can be related only for every flash light , as a particular case !
It’s definitely a function of wattage and size.
High power small lights will need stepdown
to keep them from self destructing.
Same power but a larger light will not need the stepdown.
You can’t really put a number on it.
Also in some lights the stepdown will not really be noticeable.
For example 1000 lumens stepping down to 700 is not something
that will make a significant difference to your eyes.
You would have to look for it to see it happen.
The example you gave of a light stepping down from 1500lm to 160lm
is not typical.
I wrote to the J5 company about their V1 Pro to see if it steps down, and I was told that it definitely does not. No mention of battery; just a blanket no. This confirms what people have said above: there’s no simple rule of thumb. Thanks all for replying.
Most lights at around 1,000lm and less doesn’t really need to step down. The excuse they use is to prolong the life of the LED emitter, but I’m yet to see a CREE emitter burning or have noticeable shorter life because running hot (I mean who uses their flashlight for 50,000hrs anyways?). They step down because the average consumer won’t understand a flashlight getting up to 70C and will see it as defective.
Although there’s a certain amount of variation between manufacturers, it’s mostly dependent on the size of the light, how it’s built and what it’s made of.
Some rules of thumb:
1. A light the size of a Convoy S2+ can sustain 300 - 400 lumens without getting dangerously hot. That’s nice, because you can use the lowest-powered version (which comes with a 3×7135 driver) at maximum output for as long as you like.
It is possible to run the highest-powered version of the S2+ (which comes with an 8×7135 driver) continuously at 800 lumens, and it won’t fail, but it will get hot enough to burn your hand! See here for djozz’s high-power S2+ tests.
2. A light the size of a Convoy BD06 can sustain about 800 lumens without getting dangerously hot. That’s perfect, because full power on a stock BD06 is about 800 lumens
3. A light the size of a Convoy X3 can sustain about 1200 lumens without getting dangerously hot. I have a custom-built X3 from 3Tronics which does exactly that. Although it steps down to 800 lumens after 40 seconds, I can bump it back up to 1200 as much as I like without trouble.
4. In general, smaller lights can sustain fewer continuous lumens, larger lights can sustain more.
5. Lights with better heatsinking will sustain more continuous lumens without frying the electronics, but (counterintuitively) get hot to the touch faster. They save the electronics by shunting the heat to the casing where it can dissipate to the surroundings, but of course, the casing’s the bit you’re holding
6. Materials are important. Aluminium is cheaper, lighter and conducts heat away better than titanium or stainless steel. Copper is highly conductive, but expensive and heavy. Brass is a compromise material which is often used for parts like pills and retaining rings. This is why most flashlights are made from aluminium nowadays.
Thanks for the response. Still being new at this, I’m picking up information here and there that isn’t directly related to the subject at hand but which is helpful. An example is seeing the Convoy S2+ on Fasttech rated at a little over 1000 lumens and on Amazon at 350. Now I see why. The model sold by Amazon must have the 7135x3 and the Fasttech the 7135x8. But looking at Fasttech made it even more confusing when I was given more than a dozen options between a couple of colors that had to do with the mAh ratings. I think Fasttech isn’t the site for beginners!
Yeah step down depends on the side and material of the light, type of LED, number of LEDs, type of MCPCB, driven current, etc.
The coast light you mentioned doesn’t need to step down for it’s size and output.
Don’t take this the wrong way, but any light that takes 3×AAA is kind of a joke anyway. Those lights just crowbar the LED right across the cells, and rely on the internal resistance of the cells to limit current. That’s why an LED with a Vf of 3V or so easily survives the nominal 4.5V of the AAAs. They drop so much voltage because of that resistance that acts as a natural ballast, that the voltage the LED only sees is about that 3V.
Those flashlights that take multiple discrete LEDs (7, 9, 15, whatever) don’t need any external resistance, and they can only handle about 20mA each before going mental (flickering, winking out, etc.).
Put a half-charged Li-ion cell across those LEDs, and they’ll go >pouf!< in seconds.
So… none of those lights would need any kind of stepdown.
The main issue is heat. If the LED would take all that current and build up all that heat, to the point of damage, then yeah, you’d need to step down the current (and thus heat) to prevent that. But even an LED that’s specced to maybe 10W maximum can be pushed to 30W or more as long as it’s kept sufficiently cool. Good thermal path, lots of surface area (fins, etc.), and preferably something else (breeze, hand, etc.) to wick away heat.
