From the BORED SHEEPLESS IN THE GREAT WHITE NORTH Dept...![](https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/?action=dlattach;attach=947702;image)
So, after another round of trawling the sea of shit known as the intardnet 'til my eyes water trying to research how to get started in MAME, I gave up and decided to play a little with something that requires little to no mental wattage. Initial testing just plugging in for a few seconds indicate that while it is quite bright, it certainly doesn't feel "20W of LED" bright. Powered up with no heat-sink, I find I can hold the module with my fingers directly under the 25mm² LED array for ~20 seconds before it gets uncomfortably hot; based on previous experiments with DC-powered LED modules this suggest 10-12W real LED power.
The numbers support a 20W rating; if you do the math it calculates out to 21.40W at 121.6VAC applied. Of course, the Devil is in the details; that assumes an ideal Power Factor of 1.0 for the LED driver. After scrutinizing the Amazon listing and several others like it, of course I found no mention of the PF of this module; so I did a little research on AliEx. Turns out these are, as I suspected, a commodity LED lighting module available all over AliEx in 54x54mm (hence the F5454 designation), 60x60mm and 60x40mm footprints in outputs from 10-100W, for $2-10 per module:
https://www.aliexpress.com/wholesale?catId=0&initiative_id=SB_20200311103841&SearchText=220v+COBBut after looking at dozens of listings, I still found no mention of the PF of these COB LEDs.
![Banging Head |O](https://www.eevblog.com/forum/Smileys/default/bangheadonwall.gif.pagespeed.ce.8iLbFYV4Bc.gif)
After poking around the module with my meter, I was not able to accurately measure the voltage drop across the COB LED array, though I did manage to break a tip on my cheap Chinese probes; after that, I decided to take what I know about most COB LEDs and extrapolate.
VF is usually ~3.2 for White LEDs; a few tenths above or below. Each LED chip in the COB is usually 3 elements in parallel with a drive of ~20mA each. There are 8x9 chips on this COB LED; so now we can do some theoretical maths: 8 x 9 = 72 chips. 0.06A x 3.2V = 0.192W/chip. 0.192 x 72 = 13.824W total. Hmmm...
My experience with LED lighting shows there is a huge variation in the Power Factor of the different LED drivers available; from an optimal PF of ~0.95 to as low as 0.65 for some really wasteful designs. Usually, higher PF comes at a cost... more dollars for better design & quality parts, so expecting high PF from a module available for US$2-3 a copy shipped is probably not reasonable.
So... a random finger in the air calculation for our module of 121.6VAC x 0.176A x 0.7 PF = 14.98 LED watts. Not that far off my 13.8 watts Wild-Ass Guess, and very typical of the kind of "optimistic ratings" we all know are common with such commodity electronic modules.
![](https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/?action=dlattach;attach=947698;image)
But the takeaway for me is much simpler: While this module is probably not a good choice for the desk lamp it was bought for, it may well be perfect for a Luxo KFM series 6" swingarm magnifier I picked up recently for next to nothing... I need to do some trial with the module to see if I like it better than the old-school T9 Circline bulb the Luxo carries.
![Tweak :-/O](https://www.eevblog.com/forum/Smileys/default/smiliey_cal.gif.pagespeed.ce.yYMcAvxBJk.gif)
Then comes the really fun part... finding a way to mount the swingarm on my desk/workbench, which has already proven very uncooperative in previous attempts.
![Angry >:(](https://www.eevblog.com/forum/Smileys/default/xangry.gif.pagespeed.ic.0w4zhwjvDw.png)
mnem
![Scared :scared:](https://www.eevblog.com/forum/Smileys/default/scared.gif.pagespeed.ce.oZptHNcbsD.gif)