the COB ( whatever that means
COB means Chip On Board, which is a manufacturing process used for a type of LED emitter. The COB produces a high dispersion light output, which isn't focused. Their use in LED bar is questionable IMO, as the light doesn't go were its needed, but those plucky Chinese like to put them in newer LED bars for some reason.
I've some older LED bars, and there's not a COB in sight.
The actual emitters used in bars has changed over the years too, most now use what the Chinese call 'beads' which are just generic 3 Watt LEDs, the main thing is they're cheap. They're not particularly good at being focused, so tend to throw light forward in a rather uncontrolled manner.
Another common emitter used in Chinese bars is the COB, which although brighter than the bead LEDs, it's even less focused, so although more light is produced, where the light goes is rather random.
Both these bar light sources are still miles brighter than conventional headlamps, but they're not optimal for longer range lighting, close up they're fine.
My light bars use CREE XB-D emitters, which have the advantage of being smaller and brighter than the current normal bar emitters.
My light bar is only 24" long, containing 42 X 3 W CREE XB-D emitters, but it'll cast usable light for over ½ a mile, which is pretty impressive for it's size and power.
The bead or COB emitters don't do this, giving lots of light within the first 100 yards or so of the bar.
But if budget is limited, you can only use what you can get.
Here's a quick example of the emitters used in budget light bars.
This is the CREE X Lamp XB-D. It's small at 2.45 mm X 2.45mm, rated at 3 Watts and is able to produce 107 lumens per Watt. Being small, it works pretty well with a reflector, as it has a tight focal point.
This is a typical Chinese LED bead. These are rated at 1 or 3 Watts (LED bars use normally use the 3W type), produce around 45 lumens per Watt, but being larger (about 5mm), don't work so well as the XB-D with a reflector, as the focal point is larger.
This is COB bead. They come in a variety of powers, from ½ a Watt up to 10s of Watts, however the higher the wattage, the larger they get. A budget light bar will use a 3 Watt COB, typically being 5mm X 5mm when using a reflector, or 6 mm X 4mm without a reflector.
These COBs produce about 40 lumens per Watt, but aren't really suitable for use with a reflector, as they have no true focal point. Instead they just throw light forward, in a rather uncontrolled manner.
