I'm joining this thread a bit late but I'm looking at LED lightbars. Apologies if someone has mentioned this already but most LED gear of any sort sold on e-bay is usually grossly exaggerated (I'm sure that's a huge surprise to no-one). This summer I had a project on and I was buying 12v 10watt LED flood lights. I tried 5 sellers, the most powerful one was 4.5 watts. Tonight I've had a quick look on e-bay and seen a seller advertising a 300w 12v CREE lightbar - but then says later that it draws 15Amps. That means it's 180 watts, and given the driver losses, probably 150 watts of light maximum. (watts = volts x amps).
And there's this one :
http://www.ebay.co.uk/itm/44-288w-C...297143?hash=item25b2b996b7:g:KSAAAOSwCQNWcHS6
Claimed 288w, 21amps @ 12v is 252w...
I'm not saying they wont be good lights, they may well be excellent but if you are disappointed, borrow a multimeter and measure the current draw....
There are a lot of over exaggerated claims on Ebay.
The classic is using the LEDs potential power rating, say your 10 Watt LED floodlight, but then the manufacturer only fitting a 3 Watt or maybe a 5 Watt driver. In this case, the lighting unit is only a 5 Watt at best. On the plus side, LED life is long, providing adequate cooling is provided.
LED lighting bars are another area of over exaggeration. Many that claim to use CREE emitters, simply don't. Using cheap, old school plastic package emitters like Epistar's. These while bright, don't offer anywhere near the claimed output.
Even CREE equipped bars often have exaggerated Lumen claims. They appear to take the maximum possible rated output of the CREE and multiply it by the number of emitters fitted. This simple won't be a realistic output. It's much safer to assume the output will be 50% less than the stated figure.
Obviously looking at the advertisement to ensure that things like the current consumption is consistent with the rated output. I also divide the rated Lumen output, by the number of LEDs. This will give an indication of exaggerated LED luminous flux. Some CREE advertised bars claim 280 Lumens per emitter, when divided down. While this is a theoretically less than potential output of newer emitters, like the CREE X-Lamp XP-G with a maximum output of 493Lm @1.5A (4.5 Watt). The output at maximum efficiency is way less at 146Lm @ 0.35A (1 Watt). The total drive current for 40 of these would also be around 14 Amps @ 3.1 Volts. Obviously we have 12 volts to play with, so actual current supply will be a lot less than 14 Amps.
I suspect that CREE advertised bars are using mid to bottom bin emitters, but claiming outputs of top bin emitters. Or they are using old emitters like the CREE X-Lamp XP-E R2. These have a 122Lm output @ 0.350A at maximum efficiency. A 20" bar fitted with 40 of these could well put out in excess of 4800 Lm. This is a more realistic figure, than the claimed 10,000+ Lm many of these bars are rated. The only slight flaw I see is drive power consumption. To achieve the Wattage claimed (120W), it would draw 10 Amps at 12 Volts. If driver is 100% efficient (unlikely). 40 XP-E R2 @ 100% Efficiency, the emitters will use 14 Amps of power at ~3.0 Volts. This is under 50 Watts, so the maths doesn't work. To get the claimed 120 Watts, they are either using distorted wattage figures. Over driving cheaper LEDs. Or they are using really inefficient power supplies to feed the emitters.
I'm planning on buying one of these budget 20" CREE bars. I plan on taking it to pieces to check it over. Then decide weather to fit it or return it. If I think it's worth fitting, I will.
