About LEDs:
The PLCC-2 size corresponds to the 3528 (3.5mm by 2.8mm), so search by either / both when finding LEDs.
The red LEDs are likely flowing about 8 mA over it, this means with a 470 ohm resistor, a white LED (what I will be using) will flow about 3.5 mA. This is important to calculate the brightness.
So searching for LEDs is fun,a s the LED size is not necessarily the same as the case size. Even if it's designed for the same solderpads as the rest of the PLCC-2 chips, a lot of LEDs overhanga bit.
Still, given a circular hole over the solder pad area, I think I'm going to go with this OSRAM LED (only partially because of their awesome datasheet)
http://www.mouser.com/ProductDetail/OSRAM-Opto-Semiconductors/LW-T6SG-V2BA-JKPL-ZI/?qs=sGAEpiMZZMvyj6n1w4pZD4dKFgDKInlf77CN6aUClfM%3dLooking at said datasheet, the Vf / If curve balances against the supply voltage / resistance characteristics at about 2.8Vf / 5mA If. Looking at
the datasheet this means it'll output about 0.3 the rated Lm, as it's designed for 20mA of current.
Now what about brightness? Since semiconductor doping is still less precise a process than we would hope, they have to test the output for colour and brightness. This is called "binning" the LED, and they sort them by some characteristics into groups or bins. The linked product spans a few brightness bins and colour bins.
LW T6SG-V2BA-JKPL-ZI
Product line: LW T6SG
Brightness bin range: V2 to BA (brighter LEDs)
Colour range: JK to PL (a bit cooler colour temp)
package type: ZI (I think this is PLCC-2 instead of TOPLED, but I'm still not sure).
This corresponds to a brightness of 900-1800 mcd or 3030-6060 mlm (3-6 lm). Operating it at 0.25 power results in .9 - 1.8 lm
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bright enough for me.
Here's the radiation characteristic graph (I like the half polar half rectilinear form of it also)