For most users of portable lighting, these three letters became a sign of the best lighting quality available. XML is advertised as 500 to 1500 lumens out of the one LED. How come that sometimes a lamp working on a few poor XP-G or one XM-L can be stronger than the "1000 lumens" one.
Cree XM-L is a single-chip high power LED, which has been produced by Cree since 2010. Its maximal permissible power supply current is 3000mA, which gives the power of 10W with 3.337V of forward voltage. They have ~20% higher effectiveness from XP-G LED, due to higher chip surface (2mm x 2mm) than XP-G (1.4 mm x 1.4mm). However it hinders focusing and optical collimator do not offer a better focusing than 9°FWHM against 6° for XP-G.
Bins – LED’s are sorted due to their effectiveness for 700mA current. Most often the seller declares LED usage from T6 and U2 bins. However browsing wholesale offers for cold colouring, the best prices are available for T3-T4 bins and no one puts them in trash bin ;).
Bin T3 – 220 lumens @ 700mA – 543 lumeny @ 2000mA – 715 lumens @ 3000mA.
Bin T4 – 240 lumens @ 700mA – 593 lumeny @ 2000mA – 780 lumens @ 3000mA.
Bin T5 – 260 lumens @ 700mA – 624 lumeny @ 2000mA – 845 lumens @ 3000mA.
Bin T6 – 280 lumens @ 700mA – 692 lumeny @ 2000mA – 910 lumens @ 3000mA.
Bin U2 – 300 lumens @ 700mA – 741 lumenów @ 2000mA – 975 lumens @ 3000mA.
Basing on the upper table single led 1000+ lumens bike lights can be shelved alongside fairy tales.
On the other hand they write “max 1000” or “up to 900” lumens so they are covered :).
Maximum current for XML is 3000mA, which can be little for some, but for drivers in torches or lights it is quite a lot especially when there is no cooling. It would also require thick cables not thin wires. In practice, most of the drivers designed for LED's do not exceed 2400-2800mA which in case of a T6 LED bin means 789 or 873 lumens. If we are “lucky” (as most eBayers) our driver does not provide more than 2000mA in the highest mode so it leaves us with barely 692 lumens on LED.
How to check whether we are “the lucky ones” at home?
Typical Chinese cells - most of the cheap cells and battery packs from eBay / Aliexpress - have the capacity ~2-2,2Ah, which means that the expected working time of a torch in top mode should last an hour, sometimes hour and 20 minutes. So why is your new super, mega, earth burning light working much longer? The answer is simple - the torch uses way less current than it supposes to, to match producer’s promises.
Hot lumens and cold lumens.
I’ve been writing about so called "LED lumens" all this time, but we should be more interested in lighting that we can get from a real torch or bike light. To reach the final value we must get through two more stages. Cree XP-G and XM-L LED's are divided into bins based on junction temperature of 25°C (only Cree XP-G2/G3 and XM-L2 have characteristics for 85°C). Anyone, who touched well-assembled torch with X-ML set on maximal mode knows that the temperature of the body is much higher than 25°C.
Measurement data are given for Magicshine MJ-808E torch in which driver provides 2430mA for LED - the expected value of declared bin T6 is 789 lumens.
Cold measurement - let’s forget about T6 bin on the color-box and based on LED characteristic card we must assume that it is, in fact, cheaper T5 ;-).
What will happen if the light gets too hot? I.e. the temperature will rise to 76°C on LED module and around 100°C on the chip? Out of 740 lumens, we are left with only 670 lumens :(.
LED lumens vs light lumens.
On the Internet, you can find a plenty of discussions about the superiority of the reflector collimators over the lens, but let’s skip it. Reflector does not reflect everything as the same glass covering reflector does not let 100% light pass. So we are losing more lumens... Luckily the final result is not that bad as intermediate data shows (maybe I exaggerated with the warming of a dismantled module) after testing a hot light we get:
Out of promised 1000 lumens, we are left with only 658 so 65,8%. In case of Magicshine bike lights, we have a nice driver and quite good heat dissipation, LEDs were also admissible. In some cases “lucky” user gets instead of 1000+ only 450-500 effective lumens, so manufacturers/sellers promises should be approached with caution. I advise comparing purchased Chinese equipment with ANSI certificated lights.
Currently on the market are quite a lot of bike light’s and torches complying with ANSI NEMA FL-1 standard so it should not be too hard to find some “real lumens” lights - at least for the first 60 seconds ;).