From the BORED SHEEPLESS IN THE GREAT WHITE NORTH Dept...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.
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.
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.
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.
mnem