Claims of performance of LED torches become more extravagant by the month it seems.

Above is an Ultrafire XML-T6 LED torch purchased on eBay for about A$25 posted. The seller claims “CREE T6 2000lm LED Zoomable Torch Flashlight 2 x 18650 4200mah AAA Batteries”.

A quick reality check

If luminous efficiency was around say 100lm/W, this torch would require 2000/100=20W, which on 4V would require a current of 20/4=5A. This represents a 1.7C discharge rate for a nominal 3000mAh battery (which is what was actually supplied), so it is unlikely to have an endurance of around half an hour.

It is unlikely that the torch achieves the claimed output, it just isn’t a practical configuration.

Cree XM-L T6 datasheet

Cree specify a minimum luminous flux of 280lm at 0.7A, and extrapolate that to 388lm at 1000mA. Maximum current is 3000mA (692lm extrapolated).

The Cree XM-L T6 cannot deliver 2000lm.

I have seen claims of well over 3000lm from torches claiming to use this chip, the claims seem to increase by the week. That is very Chinese.

The reality

Measurements were made of current consumption and light output.

Current consumption

In the three steady modes, current on a 4.3V supply were 1.0A, 0.5A, and 0.2A.

Light output

A small number of spot measurements were made at full power (1000mA), max and min zoom using a Mastech MS6612 Digital Lux Meter. Note that the few spot measurements leads to some uncertainty in the total flux, and the figures depart from the spec sheet a little.

At min zoom, 660lx over a 1m circle gives 518lm flux (~30% higher than specifications) giving a luminous efficiency of 518/4.3=120lm/W (which is very good).

At max zoom, 6000lx over a 0.2m square gives 240lm flux giving a luminous efficiency of 240/4.3=56lm/W (which is a bit ordinary for an LED).This is about half the light output at min zoom and indicates the poorer optical efficiency at max zoom.

Good LED torches maintain constant light output until the battery voltage falls to the minimum safe cell voltage (~3.3V for the supplied Li-ion) at which point it turns off to protect the battery from damage.

This torch did none of those things, light output fell as the battery voltage fell, and it still produced light at 2.5V battery voltage, way below the point at which a Li-ion cell would be permanently damaged.

We might expect light output to fall as the LED gets hot, but this was not tested.

Batteries and charger

The torch was supplied with batteries and charger.

The supplied batteries were tested and reported in detail at Chinese 18650 Li-ion cells – Ultrafire capacity test.

Essentially, the cells were low in capacity, and the charger did not charge to sufficient voltage to fully charge the cells, the net effect was about 20% of the advertised capacity was available.

Endurance at full output on the supplied cells using the supplied charger was about half an hour.

A protected 18650 cell would be a wise investment to reduce the risk of permanent battery damage lest the torch be left on. The torch accommodates up to 70mm long batteries which should accommodate a protection PCB on most common cells.

Controller board / modes

The torch has five modes. The description claims mode memory, but it seems that merely means that every time it is switched on, it advances one mode from last time. The lack of effective mode memory makes for very poor usability.

It appears it is possible to defeat this process by padding a capacitor with a resistor so that it loses its memory in a couple of seconds and defaults to turn on reliably in high intensity mode, from which base one can click it down to the other modes (med, low, flash, SOS).

Modification

For those who are experienced in SM rework, here is what I did.

Unscrew the lens to expose the front assembly above.

Secure the body of the torch and using a pin wrench in the holes above in the silver ring, unscrew the front assembly.

Slide the zoom ring off the front assembly.

Gently prize the driver board from the back end of the front assembly.

Carefully solder a 100k resistor piggybacked onto the only capacitor on the board. You can see the resistor in the top right of the pic above (initially I tried 22k hence the 223 marking but was replaced with 100k).

If you are competent with this rework, you will know that excessive heat will unsolder the cap and all, and you will probably destroy it or just lose it. To the competent, this is a really simple operation.

Now gently press the driver board back into the rebate in the front assembly, making sure it is secure.

Reverse the disassembly procedure, cleaning the LED and lens, and test your handiwork.

This mod makes the unusable torch usable, though not good.

My warranty: if you break it, you get to keep both parts.

Counterfeit or genuine?

As with most Chinese product purchased online, one had little assurance that products are as labelled, whether the ratings or the claims of brand name (eg CREE in this case).

Cheap and nasty

You have heard the expression “cheap and nasty”, well despite rather nice build quality, this torch has much lower light output than claimed (and that is due to extravagant product claims), lower capacity batteries, an inadequate charger, and no protection against over discharge of the battery.

More…

Ultrafire XML-T6 LED torch – a fix for the dysfunctional mode memory ‘feature’