Bicycle headlight with 6x CREE XM-L T6 LED 7800LM

K

kifukarider

10 W
Joined
May 6, 2013
Messages
71
I highly recommend this headlight. I got it new for around $50 on ebay. It's advertised at 7800LM and when compared to the NightRider Pro 3600LM for $600+ it's an easy choice. The high beam is overkill for street and low is more than enough. The high beam would be great for offroad where you're not afraid of blinding oncoming traffic. It also has a blink mode which is pretty obnoxious and should probably only be used at raves or nightclubs. My only complaint so far is that it's attached by a rubber band. It is a very high quality rubber band, but still. With the $550 saved though, there are funds for mounting upgrades should they prove necessary.
 
Please post the ebay link. I have not had the same experience from all ebay light sellers :(
 
That is about 75 watts. It's like a car headlight.

Edit: Actually, I'm way off. Car hids are only 35w and lower efficiency. In 55W halogen terms, you have 3 cars worth of light. I really don't think it is needed. I'm sure most batteries would agree.
 
Thanks for the reference. I found them when I searched earlier. They have a full range from 1 to 6x LED. Always nice to hear about a good experience with a vendor.
 
friendly1uk said:
That is about 75 watts. It's like a car headlight.

Edit: Actually, I'm way off. Car hids are only 35w and lower efficiency. In 55W halogen terms, you have 3 cars worth of light. I really don't think it is needed. I'm sure most batteries would agree.
Click to expand...

That is an interesting point. The high does seem like overkill on the street. I'm am curious to put an amp meter on it now. In any case, the low is very nice. There are also models with 1 CREE XM-L LED, 2, 3, 4 and 5 so there are a range of options. I went for the 6x since it was the brightest I could find. I think the most interesting aspect is the price/performance. All models come with the same battery pack though, so it's a trade-off. I'll try to keep account of the time the pack will run the light and post an update.
 
I wish there was an easy way to measure light output, it would be nice to compare real lumen output of the many lights out there, and there are frequently different ebay sellers with different claims for lights that look exactly the same. I'm sure some are quoting the theoretical maximum output of the led maker rather than what the light outputs. I have a few different lights, different numbers of leds but comparing the claimed output to the way they appear in use seems to bear little relationship to a comparison of real output.
 
alsmith said:
I wish there was an easy way to measure light output, it would be nice to compare real lumen output of the many lights out there, and there are frequently different ebay sellers with different claims for lights that look exactly the same. I'm sure some are quoting the theoretical maximum output of the led maker rather than what the light outputs. I have a few different lights, different numbers of leds but comparing the claimed output to the way they appear in use seems to bear little relationship to a comparison of real output.
Click to expand...

The battery power supply is rated at 8.4 volts and I measured 8 volts (I haven't charged it at all yet since new). I plugged in a DC benchtop power supply to the light and it displayed 2.13 amps at 8 volts on high, so 17 watts. On low it was 0.42A (3.36W) and blink looked about 1A though it was a moving target.

The CREE XM-L http://www.cree.com/~/media/Files/C...d Modules/XLamp/Data and Binning/XLampXML.pdf spec sheet says 100 lumens per watt. I would say it's more likely that the light I bought is outputting 1800 lumens on high. This estimate is also based on other calculations I did using the forward voltage graph and lumens per mA chart.

The advertised 7800LM appears to be a theoretical peak output unobtainable with the provided power supply.

I experimented with the benchtop DC power supply some more and found that amperage stayed stable near 2.1 amps even when the volts where raised significantly (my PS can go up to 3A). I got up to 17 volts before chickening out. The light did get brighter as the volts went up. I don't think it was twice as bright at 17 volts as it was at 8 volts. I have nothing to accurately measure the light output though.
 
Perception of light output is logarithmic, like loudness, meaning it takes about ten times as much light energy to appear twice as bright. Greater brightness in this case mostly buys you a greater distance that you can see illuminated objects (as long as you aren't being dazzled by close-up illuminated objects).
 
i'm not sure that 6x full powered xm-l leds are possible in such a small space. as someone said before: this would be 60w+.
my single xm-l led, fed with 3a driver uses 10w, and get's REALLY hot. if you don't move the bike (producing wind for cooling), you can't touch it after 5-10min. and it's a full aluminium body, and i did some mods to ensure good heat transfer from the led to the case.
 
kifukarider said:
I experimented with the benchtop DC power supply some more and found that amperage stayed stable near 2.1 amps even when the volts where raised significantly (my PS can go up to 3A). I got up to 17 volts before chickening out. The light did get brighter as the volts went up. I don't think it was twice as bright at 17 volts as it was at 8 volts. I have nothing to accurately measure the light output though.
Click to expand...
that's how leds work. leds need a CC (constant current) power supply/driver. if you use a simple power supply to feed a led directly it will break, because it takes more amps than it can handle. i don't know how those leds are connected internally, but 3.5v and 3a (equals 10w with loss) is a good value to get maximum output for a single led. so 17v seems reasonable if the leds are in series. another "problem" i found in these leds is, that the power cables are way to thin to carry the power needed. for a single led this may be sufficient, but for 6leds ....
 
izeman said:
kifukarider said:
I experimented with the benchtop DC power supply some more and found that amperage stayed stable near 2.1 amps even when the volts where raised significantly (my PS can go up to 3A). I got up to 17 volts before chickening out. The light did get brighter as the volts went up. I don't think it was twice as bright at 17 volts as it was at 8 volts. I have nothing to accurately measure the light output though.
Click to expand...
that's how leds work. leds need a CC (constant current) power supply/driver. if you use a simple power supply to feed a led directly it will break, because it takes more amps than it can handle. i don't know how those leds are connected internally, but 3.5v and 3a (equals 10w with loss) is a good value to get maximum output for a single led. so 17v seems reasonable if the leds are in series. another "problem" i found in these leds is, that the power cables are way to thin to carry the power needed. for a single led this may be sufficient, but for 6leds ....
Click to expand...

Agreed, constant current or pulsing current not overly exceeding the max CC is needed for LEDs. The light has resisted my attempts to disassemble it, but I would like to look at it's internal circuitry as well. I did later go up to 25 volts and it did get warmer (hot at the base) but seems no worse for wear. Hard to tell what the max voltage is until the magic smoke escapes. Perhaps the multiple LEDs benefit more from cooler running (less heat losses) than brighter output.
 
hmmm. when i bought a light i also asked me the question: how many leds? will a 2, or 3 led model give more light than a 1 led one? of course yes, you would say. but i'm not sure. this 6 led model surely does not give as much light as i theoretically could.
i would say: don't give up. we are like indiana jones, also investigating ;) open it and see how it works.
still i don't think that the little passively cooled mass is enough to dissipate 60w of heat from the led's base.
on the other hand: maybe just trim it to how much light you need and want and be happy as is - maybe the wiser way to do it *ggg* (would have saved me a lot of money)
 
izeman said:
hmmm. when i bought a light i also asked me the question: how many leds? will a 2, or 3 led model give more light than a 1 led one? of course yes, you would say. but i'm not sure. this 6 led model surely does not give as much light as i theoretically could.
i would say: don't give up. we are like indiana jones, also investigating ;) open it and see how it works.
still i don't think that the little passively cooled mass is enough to dissipate 60w of heat from the led's base.
on the other hand: maybe just trim it to how much light you need and want and be happy as is - maybe the wiser way to do it *ggg* (would have saved me a lot of money)
Click to expand...

I've summoned the power of Indiana Jones and was able to unscrew the lens. It took an unexpected level of torque, but once it budged it was relatively easy. Here are the pictures of the opened light. The circuit board is clearly glued and I'm not yet motivated to disassemble it further since it's a great functioning light. There is a wound toroid inside, but not much else visible. I am certainly happy with the light as is. It would be nice to find out how much the input power the light can handle, but it more than meets my needs so far. My experimentation has been for the benefit of the forum.

lH7eK6f.jpg

wZ2LQuh.jpg

wiZ3MMb.jpg

5f054kg.jpg

QfV1GYj.jpg
 
My Magicshine MJ 880 draws 25W on high at 8V and it is regarded as a 2000 lumen light (advertised as 2200 lumens) so I'd say the 1800 lumen estimate is about right. Runs well off Lyen's DC-DC converter as long as you heatsink it! The light which has good heatsinking still gets too hot if you're not moving when on max.
 
@kifukarider:

Does the LED "carrier" face have complete contact to the enclosure?

Is there a big PCB for all LEDs or are there 6 single PCBs?
 
izeman said:
kifukarider said:
I experimented with the benchtop DC power supply some more and found that amperage stayed stable near 2.1 amps even when the volts where raised significantly (my PS can go up to 3A). I got up to 17 volts before chickening out. The light did get brighter as the volts went up. I don't think it was twice as bright at 17 volts as it was at 8 volts. I have nothing to accurately measure the light output though.
Click to expand...
that's how leds work. leds need a CC (constant current) power supply/driver. if you use a simple power supply to feed a led directly it will break, because it takes more amps than it can handle. i don't know how those leds are connected internally, but 3.5v and 3a (equals 10w with loss) is a good value to get maximum output for a single led. so 17v seems reasonable if the leds are in series. another "problem" i found in these leds is, that the power cables are way to thin to carry the power needed. for a single led this may be sufficient, but for 6leds ....
Click to expand...
I'm still fuzzy about voltage for these LED lights. Can some one please explain to me?

LEDs have a forward voltage range, xx to yy. Below xx, the LED does not light up. Above yy, the LED dies. That's how I understand it.
Question: So how can the above 8V to 17V scenario work on the same light?
 
I've got one of these and was curious about the light output as well. 1800 lm sounds reasonable. Pretty good for $50 on Ebay and the 3 modes are very convenient, though the strobing mode is way too bright to be used at night.

You need a decent dc-dc converter though, it killed the 3A/15w "QSKJ" one (the black one that EM3EV sells) pretty quickly, but I have a "90w rated" (still 3A) Blue QSKJ one with a larger case and that one seems fine, although it still gets very hot.
 
For what it's worth, the 1,200 - 1,500 lumen CREE lamps that were running >=$60 each six months ago are running about $15-$20 on Amazon right now.

Combine one of these with a cheap, clear-back towing reflector (<$2), and you'll have a rear light brighter than just about anything else on the market.
 
The magicshine rear would take some beating for brightness. And it's designed as a rear light so light spread should be better than a modified front light. I'm not so keen on the weird switch but love the brightness- one guy walked about 50 yards to see what was making so much light.

From my experience the lights with multiple leds don't have as good or well controlled light pattern as a single led light negating some of the advantage of a multiple led light. There are a number of lights now with 2, 3, and 5 full sized reflector light built into one unit- bigger but the beam has to be better than the one from smaller reflectors.

 
So glad I've found this post! I was wondering if I could run these headlights from a 12V DC-DC without long term issues.


BTW you can get a single led headlight for less than 10$ :D

http://www.ebay.com/itm/Hot-hysg-Sale-CREE-XM-L-T6-LED-Bicycle-bike-HeadLight-Lamp-Bicycle-Light-/281111714469?pt=LH_DefaultDomain_0&hash=item4173905aa5

I guess 12V would be too much for the 4V version.
 
hungarianguy said:
BTW you can get a single led headlight for less than 10$ :D

http://www.ebay.com/itm/Hot-hysg-Sale-CREE-XM-L-T6-LED-Bicycle-bike-HeadLight-Lamp-Bicycle-Light-/281111714469?pt=LH_DefaultDomain_0&hash=item4173905aa5
Click to expand...

Unless I'm reading it wrong, you get the light and the charger for $10, but no battery? Would make sense to buy like that if you're running off a DC-DC converter from the main battery, but otherwise, you'll still need to power it.
 
spisska said:
hungarianguy said:
BTW you can get a single led headlight for less than 10$ :D

http://www.ebay.com/itm/Hot-hysg-Sale-CREE-XM-L-T6-LED-Bicycle-bike-HeadLight-Lamp-Bicycle-Light-/281111714469?pt=LH_DefaultDomain_0&hash=item4173905aa5
Click to expand...

Unless I'm reading it wrong, you get the light and the charger for $10, but no battery? Would make sense to buy like that if you're running off a DC-DC converter from the main battery, but otherwise, you'll still need to power it.
Click to expand...

This is called buying choice. Someone would complain if you can't buy without a battery, you post because you can.

Customers buy what they need, support the suppliers who let people buy only what they need.

It would make sense for me- my light was stolen but the battery is still there.
 
You must log in or register to reply here.
Back
Top