What is wrong with those Chinese flashlights?

I've bought several of the flashlights sold in Chinese webpages, and on eBay. They are supposed to have very good LEDs, similar to those used on high-end brand-name flashlights (eg. the XM-L T6). Now these flashlights come nowhere near their advertised lumen output. That's somewhat expected given that certain vendors list higher lumens than the max lumen output of the LED, but let's say I'd want to reach the max LED lumen output, or even slightly below that. What is wrong with the flashlight being so dim? Do they use fake LEDs, or is it a junk driver?

I would really hate to pay big $$ to get a brand-name flashlight just to get its rated lumens. The body of those Chinese ones is pretty good, and if the LED is genuine, then the only thing I need to change is the driver, am I right? Has anyone tried changing the driver, and noticed big changes? Are the LEDs fake or genuine?

Could be a combination of many things, such as driver, LED, and poor heatsinking.

What exactly did you get? As far as I know, there aren't any fake Cree X-Lamp models, do if it looks like an XM-L/2 or XP-G/2, it probably is. Can you take a photo of the LED?

Even with "good" Chinese flashlights, the lumens claim is often exaggerated. A stock XM-L/2 flashlight will almost certainly never hit 900 or 1,200 advertised lumens, more like 600-650.

It depends what flashlight it is but yes, most will have an XML emitter (generally speaking), which is a genuine Cree emitter. 99% of the time cheap flashlights will have very crap drivers that do not drive the led to even half it's max rating.

Often you can mod the driver with different resistor values to increase the current to the led but often it is easier just to replace the driver. With that being said you can't do anything unless you know the specifications of the flashlight in question.

You need to tell us what flashlight you have in mind. For all I know you could be referring to a police flashlight that is worth 2 bucks.

will manners said:

For all I know you could be referring to a police flashlight that is worth 2 bucks.

Click to expand...

Not even $2, you couldn't pay me to take them! :na:

I'll give you a prime example which illustrates my point, eBay item number 321164610527

Awesome price, Great body, and possibly a genuine Cree LED. The light output sucks though. How do I fix this? Is it the driver?


Poor heatsinking is out of the question, because lumen output is more or less steady throughout the use of the light

This forum is very helpful btw!

What I find really interesting is that the company that produces the Cree emitters are actually produced in North Carolina. The way I see it the big brands companies bid on a contract to get the desired binn from Cree of any certain emitter then produce the host drivers and host from there.

I have researched the company Olight and they really put the cobash on all the P binn SST 90 back in the day.

What cells are you using? If you're using 3x AAA, the batteries can't supply the current.

The optics also block a lot of light. Out of the lens, you're probably getting 50-60% of what the LED is emitting.

Driver is circuitry between the battery and LED that regulates power to the LED. If the driver is set to only power the LED with low current, your LED will be dim.

Battery. As someone else mentioned, some batteries aren't designed for high power output. For performance flashlights, you will generally have to ditch alkalines like AA or AAA.

If that Zoom light is the one you purchased, consider buying a name brand protected 18650 cell and charger. You will likely notice it gets much brighter on the rechargable 18650. Not to mention, the 18650 will last longer on one charge than 3 AAA batteries.

Avoid ____fire cells. Name brands are panasonic, sanyo, sony, etc. If you need cells of different size than 18650, look for AW lithium ion. Folks here will post up more specific recommendations if you ask.

The sellers do the same things with lasers. Most people don't have equipment to measure their claims or enough knowledge to question it.

There are some great cheap lights out there and a lot of them can be made better with a few simple mods. You definitely should venture over to BudgetLightForum.com and poke around.

I am only using rechargeable 18650 cells. I have a pair that I've purchased from DX, and a set of 4 Nitecore ones that I got from Amazon. Both seem to power the same lights with the same amount of current (visually same lumen output). I do not use AAA ones at all. So batteries do not seem to be the problem.

I am thinking of getting a new driver for the one light that I've posted above. That *should* answer my question (as to what the problem is). I've also got other lights which seem to have the same problem and I'll test those too when I get the time.

mhemling33: I'll check the link but since I have little time what kinds of mods are people generally talking about? Driver mods? Optics? Heatsinking? What's going to give me the most bang-for-buck?

Thanks

If it never gets bright, not even for a second, then a driver swap will probably be the most bang for the buck. I don't know what the heatsinking on that light is like, but with an alright heatsink, you should be able to find a cheap AMC7135-based 2.8A driver for it that will run the LED a bit brighter. And if you find that 2.8A is a bit too high for the LED, i.e. if it dims after turning on because of poor heatsinking, you can remove a chip or two from the driver, each chip allows 350mA through.

This is the LED and the driver below it (for the eBay flashlight posted above):

Photo

I am still not sure if the LED is genuine, as I've seen the "Cree" and other details written onto the LED's surrounding white space in some youtube videos. I couldn't remove the driver from the housing (it's pretty tight and didn't want to break it at least not now).

I used a PC PSU to supply +5V DC to the driver, and got some voltage measurements across the LED. With a +5V input voltage, the LED was being driven at 2.91V, 2.81V, 2.57V (3 modes, high, med, low). I do not know what current was passing, as I did not want to cut the cables. I also did not find a voltage-current diagram for the LED with a quick search (is there?). The genuine LED's typical "forward" voltage (the typical voltage to drive this LED, correct?) is 3.1 Volts so there was still room for more lumens I guessed, so I hooked it momentarily to the +12V rail, which made it noticeably brighter. It dimmed and smoked (a little) after ~1 sec, so I used the canned air liquid to cool it down and that way I was able to keep it on for more time, enough to take a voltage measurement. The voltage was over 3.1 Volts, but not much more (didn't write it down, and can't recall).

With that being said, the only time this LED dimmed due to heat, was when I used +12V (the LED was as is in the photo, in mid-air). I believe, therefore, that heatsinking during normal operation is not an issue. What do you think of the voltage that the driver gives out, is it low? Is the LED genuine?

BTW, something got burned in the driver, and now the flashlight only operates at one mode. I wish I could do that on purpose and relieve myself from the 5 modes all drivers have. Do you know how I could make a 5 or 3 mode driver operate at only the highest mode?

Decent drivers are usually designed from years of experience, comparing several reference designs, countless hours of prototyping, component selection etc. Drivers of high end lights are fast becoming trade secrets. Budget level lights often [not always] employ driver circuits copied verbatim from datasheets then shoehorned into flashlights... or simply employ a mass produced driver board and stuff it with a matching battery size. Most datasheet examples are pretty solid, but they are there to get you going on optimizing, for they are in many instances way too generalized to fit any specific application. Many of them are simply boost or buck converters with a lousy feedback loop filled with noise, stray inductance, etc that hamper a good steady regulation.

There's three [or actually four] main qualities necessary to produce a good light: Electrical, thermal, optical, mechanical.

Electrical efficiency is important because at the design level flashlights run on batteries. Batteries have limited juice, and in many instances the forward voltage of the LED is so close to the voltage of the battery that any inline resistance contributed by mechanical fittings may reduce its performance. Poor circuit design may cause absurd current drain without providing much current to the LED. The battery gives out before the regulation sets in the driver drops out of regulation and the user isn't happy, happens all the time. Yes, you could change the driver and it might work out, but you'll have to make sure the thermal considerations have been given thought. There are manufacturers that have produced lights that were thermally deficient around the LED and drove them underspec to get away with it. Swapping in an in-spec driver in this situation will cook the LED

Thermally it should be pretty self explanatory: things heat up, and heat only promotes efficiency at the battery level. Driver produces heat, LED produces heat. A hot driver loses efficiency, a hot LED loses efficacy. Poorly heatsinked and neither may outlast a full set of batteries. Sure, you could build a custom heatsink stool for the LED to sit on and put a new driver in to ensure nothing burns up...but do you really want to go that far?.

Optically speaking, each type of LED possesses a different radiation pattern. Optical loss on premium lights may be as low as 20%, with budget lights, mass produced generic reflectors, noncoated polycarbonate optics.... you could lose 40% of your output easily. This is difficult to change and its somewhat of a permanent limitation unless your intention of utilizing this light is as a host only. Moddrs have long taken on the robustness of maglites, strip out the plastic reflector, mount LEDs with dedicated reflectors, and add a pyrex window. 15 lumens to 2500 lumens! Somewhere down the line you have to decide for yourself whether the resulting benefits outweigh the additional investment, and there isn't really a unit of measure for it.

Mechanically you're light is a tool. You want to have reliability down pat unless its a toy. If there's metal shavings all over inside, rough edges, defect prone switch, anything that could short circuit one contact to another, its best to walk away from it.

The rest is marketing. Find the efficacy of the LED at Tj=25C driven at 350mA, look up the Relative Luminous flux to current chart on the datasheet, then multiply the known efficacy by the gain created by peak driver current... voila, you now have a huge unrealistic disproportional lumen output that's based on real data. In reality, that is instantaneous emitter output only, or "bulb lumens" when you first turn it on. Its the "Out the front lumens" that we really want to know before buying, that is, the output that manages to leave the glass. It could be as low as maybe 60% of bulb lumens. Worser still, LED junction temperatures run at a way more realistic 85C, so remember to de-rate the output even further.

On a side note, you really do get what you pay for. Judging the light by the looks alone is like buying a waterlogged car because it had new wax. You can have the best LED, best driver, best reflector, and best body. But if none of them are truly compatible, its not going to win the best of any awards