I happened on to two of the last few remaining penlights from the BLF 348 special build from Singfire. For those who don't know, they are simple single AAA/10400 penlights with a Nichia NVSW219BT emitter. For a $10 light, they are really fantastic! They have the characteristic Nichia 219 color rendition, with a very diffuse hot spot that just kind of spreads all over the beam. I tried using a 10440, but it got very hot very fast, and isn't really recommended since the stainless steel doesn't conduct head away very fast. But even with a single AAA it does a great job. I wanted to get a couple more but they are now out of stock, with no idea if there will be another build or not.