After having come across by accident some information about COB LED's it seems that a COB (chip on board) LED would make a good flashlight for some kind of purpose since it can be obtained in a rather small diameter and it can put out about 100-130lm/w. There are other multiple advantages as well. This page has a comparison of a Ceramic COB LED vs an Aluminum COB LED vs a typical high power single LED.
Just to quote something from the page above "COB LEDs have great advantage of thermal resistance, larger cooling area, better lighting effect and high light efficacy."
Since I am an BLF Illumination Engineer-in-training (and at the very start of my training yet!) can one or more of our "Elite BLF Scientists" or anyone else chime in as to if the idea of a COB LED Flashlight would be plausible and practical? Come on - do not be shy.
The main website for the COB LED's from the above links have much more information.
I think we already use a kind of COB but better. Isn’t what we call the emitter, a chip? And the instead of a circuit board, we attach it to a star?
Comparing the thermal properties of multiple low powered LEDs on a large ceramic board to a single high powered LED on a small copper star isn’t fair. Multiple LEDs on copper will run cooler than on ceramic and a single LED on ceramic will run hotter than on copper. The only disadvantage with copper is that you have to run wires to each LED.
To make sure we’re all on the same page: COB is not a brand name, it’s just a descriptive acronym.
COB LEDs are cheap. They don’t do anything better than traditional “Power LED” devices other than cost. They also typically offer an increased light emitting surface area per cost, which is different - not better or worse. In the case of flashlights, an increased light emitting surface area is not something we want. Since everything else about COB LEDs is the same or worse than Power LEDs, we stick with Power LEDs.
Many COB LEDs use a ceramic substrate rather than circuit board. And those that do are just multiple LED versions quite similar to the power LEDs we use. In fact Cree's CXA (Edit: and even the MT-G2) is considered a COB led. The big difference is in how much light is produced per watt, that's where Cree shines.
Typically the COB LEDs are meant for broad coverage - plenty of spill. Think light bulb. Because of the emitting area size they are nearly impossible to focus into a tight beam for typical flashlight use. On the other hand if a wide flood is what you want then these are an option.
For efficiency and flood, multiple low power LEDs are better but it shouldn’t be compared to a single LED on a star commonly used for it’s compactness. COB doesn’t need copper if the power to each LED is low and they’re well-spaced but a single high powered LED does. COB serves one purpose and a copper star, another.
Sure, the MT-G2 and XHP50/XHP70 are arrays… but AFAIK the COB term has traditionally been applied to the scenario where we plunk down a bunch of chips and then pour phosphor over top of them. (Or use other money-saving tricks. In other words I’ve always seen the term COB used in the ‘cheap’ context. Never to a power LED whether it’s got 1 chip or >1 chip.)
If I sit down somewhere and say “bring me your finest COB LED” I don’t think a waiter is going to show up with an MT-G2, MK-R, or XHP70.
This is not a picture of a COB LED. That’s just a bunch of mid-power LEDs soldered onto aluminum MCPCB. Not what the link in the OP is talking about and not what COB means in any sense.
I have been eying the Philips 'crispy white' COB led, it is round, just 10mm diameter, the high CRI version has extremely good colour reproduction, is apparently very uniform in brightness over the entire surface, and in combination with an aspheric lens would make a great big-spot flashlight. But the 34V spoils it all :-(
I know it’s not referring to a cob of corn. I may be wrong but that’s what I bought many years ago sold as an early COB. …or maybe I’m just not remembering correctly.
You are not remembering correctly or you were hoodwinked. COB does mean something, and mid-power LED packages soldered onto an MCPCB is not it. Generally speaking that’s precisely what the cheapest COB units are intended to replace! What you pictured is much more similar to the 3rd diagram than the 1st or 2nd.
