Thorfire PF01S is a single-AAA size pen light. Thorfire asked me to review the newest revision and they sent me a sample without cost for that purpose. I received a small, tan colored cardboard box with some minimal product labeling on the outside. Inside the box I found a PF01S pen light, a small English-only user manual containing a feature list, instructions for usage and maintenance, and warranty, a pair of replacement o-rings in a small Zip-loc style bag, and a packing invoice. The light was itself wrapped in a sleeve of bubble-wrap and there was a piece of soft foam in the bottom of the box. The light has a clip already installed, clipped around the battery tube. There is no lanyard included with the light.
Thorfire’s website still shows the older PF01 penlight, with no mention of the PF01S. I find this strange, considering that the PF01S has already been out for a while now. You can find the PF01S in various places around the internet. Amazon has a listing for the PF01S with text outlining some of the upgrades, for example. Anyway, of the PF01, Thorfire says that it is “Small but bright.” (and the newer PF01S is brighter) and “Simple but functional.” Hopefully, after reading this review, you’ll be able to decide for yourself whether these claims are confirmed or denied.
The first impression I got when I opened the box is that this is a nice looking little light, though not my usual style preference. I generally don’t carry pen lights. I have a tiny DQG Hobi on my keychain, and I also EDC a Olight S1A Baton. For a AAA size light, the PF01S is a bit large at 95mm long and 15mm wide (not counting the clip). It was actually shortened from the PF01’s length of 105mm. But there are plenty of AAA lights out there that are at least a bit smaller, and in some cases, very much smaller. Even so, it’s not the end of the world. The PF01S still fits nicely in my hand and is barely a bit longer than the width of my palm. So, for real flashlight use, it doesn’t feel huge. It’s actually a nice size.
The PF01S includes a boost driver so that it can run on a single AAA cell. The driver includes three modes. It moves through the modes in the order LO-MED-HI. The older PF01 included also a strobe mode, which Thorfire thankfully removed from the PF01S. Since the tail switch is a forward clicky, the modes are changed while the light is off by bumping the switch. I’m so accustomed to reverse clicky switches that it has taken me some time to adjust to the timing involved. The first bump only shows you what mode you’re already in. The light does have last mode memory, so it will come on in whatever mode you had it in last time you turned it off. The first bump needs to be quickly followed by the second, and possibly third, etc. switch bumps until the desired mode is selected. The light will flash at the level of each mode as you press the switch. When you get to the desired light level, the switch can be fully pressed to turn the light solidly on. Honestly, I think forward clickies are great for signaling using single mode lights. For any light that has more than one mode, give me a reverse clicky or a side e-switch. 
Beam profile is something that is very unimportant to me. I said this in my review of the Olight S1A a while back. But, again, I realize that people will want to know this information, so I’ll do my best to describe it. The Olight S1A uses a TIR, so the beam is a bit wide compared to reflector lights. However, usually we’d expect bigger reflectors to make tighter spots and smaller reflectors to make wider, more diffuse spots. The PF01S reflector is narrower than the TIR in my S1A by about 50% or so. But, in just about five feet from the top of my desk to the ceiling in my office, the hot spot of the S1A is about double that of the PF01S. Without trying to actually measure, it looks like the hot spot of the PF01S at that short distance is about 10 to 12 inches wide. The edge of the beam and the corona seem smooth to my eyes. I can’t detect any strange artifacts in the beam, probably due to the light OP finish on the reflector. I’d say the beam is fairly tight considering the small reflector diameter. It should be useful for most general purpose flashlight needs.
The PF01S doesn’t claim Li-Ion compatibility. For myself, I wouldn’t have even tried it. But, since I know a lot of people are going to want to know, I did put a 10440 in it to see what would happen. The low mode is still very low. It must be fairly well regulated. I didn’t notice a change in the brightness from a NiMH AAA cell to the Li-Ion 10440 cell. I don’t have an accurate way to test brightness levels, so I’m mostly guessing. I used my phone with a luxmeter app to get a closer guess, but I didn’t do it the least bit scientifically, so don’t hold me to anything. The mid mode was significantly brighter with my 10440 versus the NiMH cell. My phone app suggests about a 60 or 70 percent gain. The high mode showed the biggest change with almost three times the lux measured by my phone. All measurements were taken at a short distance (about a foot from the light to the phone’s sensor). By eye, shining at a distant wall, it looked like at least double the light output to me on high mode.
The flashlight didn’t get significantly warm, even on the highest mode, while using the NiMH cell. But, when I switched to the 10440, it didn’t take long to feel warm on high. I could tell it was warming up at around 10 seconds. By 20 seconds it felt warm at the head. I shut the light off at 45 seconds because it isn’t rated for lithium use and I was worried the driver might fry. It didn’t want to do that yet, for a few reasons. One reason is that I just don’t want to fry a driver right now. It’s not my idea of fun. Second is that the head seems to be glued. I tried to take it apart and scarred the anodize on the battery tube with my cheap vise, even though I padded it to try to protect the light from scratching. If I can’t get it open, I can’t replace a bad driver. Third reason is that I don’t actually have a driver lying around to replace it with right now.
I’ve mentioned that the light is a bit large for being AAA format light. The tail-cap looks particularly big to me for the size of the light. Additionally, the button protrudes past the end of the tail-cap by several millimeters. Since the button cover is rubber and not flat on the end, there is no tail-standing capability with this light. The protruding button should make it easy to turn the light on/off with gloves, however, so there’s that. The head is one piece without a separate bezel. But the business end is crenelated, which should make a few people happy, since it will be possible to see if the light is on while head-standing. The knurling, if you can call it that, is really just for decoration. Since it doesn’t improve grip, I’d have preferred the tube to be left smooth, as I like that look better.
I’ve already compared the beam profile to my Olight S1A, but let me see if there can be other comparisons drawn, in order to give a better idea of this light’s capabilities. Sticking with the Olight, we could talk about the PF01S “low” mode, which is actually more of a moonlight mode, since it is visibly dimmer than the moonlight mode of my S1A, even with a 10440 in the PF01S. The clip is a simpler design, but, I think, better than Olight’s clip. It takes a bit of effort to clip it onto belts or thicker pockets, but it at least holds onto the light, which the Olight clips have failed to do at times. There’s a band, or groove, on each end of the battery tube for the clip, so it can be used in either forward or backward orientation. On the downside, the cheap anodize on the PF01S means that moving the clip around or trying to remove it will scratch the light. :rage:
Compared to other AAA size lights I’ve used, the PF01S is larger, as I’ve mentioned, but a bit more capable, having three modes, including a low-low, and a plenty bright high, especially with 10440 cells. And compared to others, it has a tighter beam profile as well. As such, I’d recommend this as a smaller, easier to carry flashlight than a single AA or 3X AAA light, or a slightly larger, yet more capable flashlight, better suited to general purpose use than some other single AAA lights I’ve seen.
I’ll try to get some pictures up later. Honestly, it’s not that special to look at (just my opinion) and there are already pictures of it on the internet. If I could get the head off, I might have something interesting to take a picture of. As usual, let me know if I’ve made any errors or left anything out.
Thanks for reading!