Okay, so penlights (pen lights?) are not the sexiest topic within medicine. However, I struggled with them a lot as a medical student. As in, I never seemed to have one when I needed one. And, when I did have one, more than once it had died when I finally tried to save the day on rounds.
I originally used this style: decent light source, reusable, available from my school bookstore. The problem is they’re activated like a pen and are easy to turn on accidentally, so they die constantly. They eat up batteries. And then I lost one. And another.
I then used these cheap disposable penlights. They’re great for several reasons: super cheap (as a cheap $1 each on Amazon) and you can only shine on purpose, so they won’t die accidentally. The problem is that they do die randomly. And the lightsource can be so weak that it won’t work in bright room. The pupil gauge is nice though.
Entering intern year I was in need of a new pen light, as my wife and I had somehow lost all of ours in the move. I looked around and splurged (relatively) on the Streamlight Stylus, which I love. It’s around $10-15 depending on the day, but it’s super bright, lasts forever (like 60 hours on one set of batteries), and is as slim as a narrow pen, so it fits easily in the pen divider of a white coat with room for another pen, so I actually use it all the time. It’s reusable, as it takes 3 AAAA batteries. That’s right. AAAA. Where do you find AAAA batteries you ask (should you rack up 60 hours of pupil gazing)? Inside of the 9V batteries you used to stick your tongue on (and online, of course). Downsides? Extremely bright, so be careful of how you use it. Also, its long length may cause it to stick out of your white coat depending on the size of the pockets.
If you want the Rolls Royce, the Foursevens Preon 2 has multiple light modes (dim for carefree direct pupil, bright for room flooding) and is generally well loved as the most versatile LED penlight around (downsides: bit wider; click button means you can leave it on by accident and waste the battery). In between is the new NexTorch Dr. K3, which costs around 24 but gives you an awesome medical grade light with Goldilocks brightness and excellent build quality.