Flooding Tower

[Tr4sHCr4fT]

Guys,

it's summer, we are doing BBQ each weekend, and like to stay there even when its dark. so we need a kind of "lantern". my plan is a 24Ah pb battery, and a 2m or 3m teleskope pole, mounting 4 floodlights.

i myself own a P7, R2 and other nice torches, but none of them is a real wide flooder. What would you recommend for the situation? like said the lamp will be in 2-3m height and shall flood a good spot under

i need advice in choosing 1. the emitter and 2. lens and reflector :?

 

[Ken_McE]

If it was me, I'd glue a high power LED to a heat sink, put a diffuser in front of it so as to not blind myself, and hang it off the pole. No lenses, no reflectors, maximum dispersion. Put a couple lights up there, each independently adjustable. As for which emitter, cool white usually gives the most lumens/watt. What voltage will your battery be?

 

[Tr4sHCr4fT]

so just slash 4 of this http://cgi.ebay.de/High-Brightness-...987?pt=LH_DefaultDomain_0&hash=item35b11c080b on it?

(looks like DX #5876 on heatsink for me)

 

[ljw2k]

http://www.lck-led.com/p701/Aluminum-10W-LED-Flood-Light---AC85-256V,-8-900LM/product_info.html might be your answer

 

[onetrickpony]

I think you're going to be happy if you put a little time into selecting the right emitters for the job. If you're using a flashlight and the color is a bit off (blue, green, purple, yellow whatever) you won't mind it, or maybe even notice it most of the time.

Take one of your flashlights, turn off the lights in a room, aim it at the ceiling and turn it on. Ask yourself if you want to hang out with people in that light. Everyone will look pretty much like zombies, in other words, their skin will look very unattractive.

Spend the couple extra bucks to get warmer leds, especially those with high CRI's (color rendition index). I think anything around 80+ will be plenty good enough for your purposes, but someone with more experience with that specific characteristic may be more helpful.

I think the XM-L is the perfect light source for your needs, but you'll want to get one below the 5000k mark for color temperature. The lower the better, really, 3000k would look almost like the light from a fire.

Keep in mind that the lower the color temperature of an led, the lower it's lumen output will be, but I think in this situation that's irrelevant, you can just add another led or two with a slightly bigger heatsink. You're not constrained by size like you are in a torch.

Don't drive anything at its maximum rating. You will find that the leds will change color and have reduced output unless they are very well heatsinked, and they are far less efficient at the highest of drive currents.

 

[Tr4sHCr4fT]

Ok, found the XM-L in a 3000K Version with Star for 8€ a shot, or 6 as bare pcb.
Do you know cheaper sources which are delivering to Germany?
Also, how about the Cree-MT-G-EasyWhite? (http://bit.ly/lXhuen)

 

[Epsilon]

Www.led-tech.de has xm-l in stock in different color temperatures :).

 

[onetrickpony]

Not to further add to the work here, but you could also try out Bridgelux es series leds. Tons of light, and not much money, plus they come in 3000k. Just another option to consider.

I believe you said you're going with a 12 SLA battery. The Bridgelux's run at a much higher Vf, so if you want to use just one, that will be a good option, very little in the way of efficiency losses due to resistors or driver circuitry.

That being said, if you use multiple XM-L's, you can hook them up in series to get the Vf you need and run them direct drive off the battery.

Aka, XM-L's have a maximum Vf of 3.5 volts. Sooo, 3.5 times 3 equals 10.5. That's close, but you're using a 12v power source, so each led will be getting 4 volts. You'd have to test this with your setup exactly as you'll have it on the beach though, because the resistance of the wires and connections may drop this down to an acceptable level. You'd have an emitter lumen output of something like 3000 lumens, which is great, but they're going to be running pretty hot, so heatsinking will be a must.

Let's add another led to get a Vf of 14 total. Each led will be getting 12/4 = 3 volts. According to the XM-L data sheet, that works out to about 1.1 amps per led. The sheet also provides a luminus flux / forward current graph, and if we look at 1100 ma we can see that it's about 135% of the brightness at test current (700ma for XM-L).

So, 1.35 * 220 (that's a T3 bin warm white) = 297 lumens per die. 297 * 4 = 1188 lumens. That may be enough, may not, but the leds will run very cool and you won't be pulling much current so you'll have a much longer run time.

Now that we've done the math, maybe a resistor or driver and 3 XM-L's is the best route, they will be very happy right up to 3 amps, above that they don't put out much more light unless they're really well cooled. Either that or direct drive a Bridgelux and maybe save some money.

 

[Tr4sHCr4fT]

Now that we've done the math, maybe a resistor or driver and 3 XM-L's is the best route, they will be very happy right up to 3 amps, above that they don't put out much more light unless they're really well cooled. Either that or direct drive a Bridgelux and maybe save some money.

Is't it so, that the XM-L are loosing efficieny the more current they get?
So having 4 emitters at lower output uses the battery better then having one at max...

 

[onetrickpony]

Is't it so, that the XM-L are loosing efficieny the more current they get?
So having 4 emitters at lower output uses the battery better then having one at max...

Yep, all led's are most efficient at lower drive currents, the higher you go, the more energy gets turned into heat. You can see this in a visual sense from the data sheet, on the luminus flux / forward current graph the line curves down as current increases, it it was the same efficiency at all currents the line would be straight.

Yes to your second question as well, and you'll see a huge increase in runtime from this setup, mostly because you'll be using about a third of the current. Let's say your battery has a rating of 20 ah, and you're using 1.1 amps. That's just about 5 hours before the battery is at half charge. BUT, this brings up the Vf / forward current factor again. Let's take a look at this one more time.

When your battery is at full charge, it's not 12 volts, it could be as high as 12.6 or so.

12.6 / 4 = 3.15 volts, so each led will be pulling more like 1.7 amps when you first fire it up. Here's the good and the bad about direct drive from a battery, as the voltage drops so does the light output. But, it's almost impossible to completely run the battery flat dead, because the leds will continue to use less and less energy as the battery loses charge, sort of a built in protection.

Now, at 1.7 amps, each led will be putting out 212.5% of luminus flux at test. 2.125 * 220 = 467.5 lumens per emitter.

467.5 * 4 = 1870 lumens at startup on a full battery. If you know what the ah rating of the battery is, you can make a pretty good guess at what the runtime will be. Say you have a 30ah battery, 30 / 1.7 = 17.64 hours. It'll actually run longer than that, because the current draw will decrease as the battery loses charge. You'd have to use it to know how long it'll go and still put out usable light, but I'm thinking plenty long enough for your needs.

 

[datiLED]

I have another take for you:

Use four SOB 1000 driver boards, each driving an XM-L LED with a wide angle (flood) optic. You will need to use a massive heatsink for each LED in order to allow it to run at 1A for an extended period of time. The bigger the heatsink, the better. In fact, they can't be too large.

 

[Tr4sHCr4fT]

Ok, how about drivers? the bad is i did'nt found really usefull 12V drivers on DX. there are some with 700mA, modable to 1A.
but one with high-mid-low mode and up to 3A for 9-14V would be the holy grail, err?

 

[onetrickpony]

Ok, how about drivers? the bad is i did'nt found really usefull 12V drivers on DX. there are some with 700mA, modable to 1A.
but one with high-mid-low mode and up to 3A for 9-14V would be the holy grail, err?

Welcome to the extremely painful and frustrating world of led lighting, it gets better, don't worry.

I think you may want to go with the least complicated of your options for now, you can always upgrade it later. There's nothing quite like seeing a project come to fruition.

Not to mention that you can be using it while you think of how to make it better. I've been up for like 25 1/2 hours straight, so I literally can't think of a driver off the top of my head, but I know there is a thread here somewhere about how to use a fairly common amc7135 driver for just about anything. Hold on, I just saw it here somewhere.

 

[onetrickpony]

Here it is: http://www.candlepowerforums.com/vb/showthread.php?201392-Poorman-Mutli-Lux-setup-method

P7's run at about the same current as XM-L's, in fact a little lower which is good. Scroll down until you find something appropriate.

EDIT: Ok, after looking at the page, you may need some help to get your 12v power source to work with something like these designs, but like I said, my brain is fried.

 

[Tr4sHCr4fT]

Nicy nicy. i think i would try the quad-LED direct drive from 12V method first.

How big do you think a heatsink must be per LED at reasonable current (1.7A max like above calculated) ?
And can i make it smaller when i use a efficient economic 12V fan mounted on each sink?
(Remeber it must be light enoug to hang stable on a 3m stative which himsel muss me light and transportable)

 

[Tr4sHCr4fT]

Gnah, the XM-L 6000k has 4V max Vf, so its ok and in Spec with direct driving a quad setup (SLA max 14,7V)
But the 3000k has 6,4V max Vf according leds.de
Can i direct drive two of them by using 3 big silizium diodes for dropping the voltage down?

 

[doctaq]

you could also look into a boost driver that will allow you to run a higher voltage in series, that would allow you to run some of the higher voltage bridgelux, even with the weird vf like 25v or such.
mouser sells some as well as ledsupply i think

 

[yazovyet]

"But the 3000k has 6,4V max Vf according leds.de"
this is contrary to every other Vf i have seen for cree xm-l s. i am going to go out on a limb and say that leds.de screwed up when they put that up. my guess would be that their error was in assuming that you could get a T6, 280 lm at 0.7A that gave you 3000k. you may also notice that it claimes the 3000k T6 maxes out at 2A instead of 3A, anohter reason i think they have an error on their site.

the cree data sheet (that is old and doesn't even have the U2 on it) says that 3000k is in the T2 or T3 range, and thus should put out less lumens (like, 200 to 220 at 0.7 A).

cree data sheet:
http://www.cree.com/products/pdf/XLampXM-L.pdf

leds.de site for the cree in question
http://www.leds.de/en/High-Power-LEDs/Cree-High-Power-LEDs/Cree-XM-L-T6-warmwhite-910-lumen.html