Despite many of today's photographers never having used one, and most likely feeling they've no need for one with all the technology packed in to modern cameras, there are still plenty of reasons to look at investing in a handheld light meter. So what do they do? Well whilst the advances within the cameras themselves continue to develop in leaps and bounds, the basic premise of the light meter's workings stay essentially the same - to measure the light in a scene to guide you when setting the camera for the image you want. Generally, you pick the ISO you're shooting at, and depending on the individual meter, it will show you the corresponding shutter speeds across the range of aperture settings, that will result in a balanced exposure.
There are 2 kinds of light meter; Reflective and Incedental. Reflective meters are the type that you usually find in your camera, light from the scene is reflected into the meter and exposure values calculated from that - whereas Incedental meters are the type you would see the photographer holding near the model measuring the light directly from within the scene. Incedental meters will give a nice accurate reading as you can take precise readings from a number of areas within the frame, but there are inherent problems in using one in the field. As you want to get as close to your subject as possible with an incedental meter, for landscape and wildlife photographers the problems are obvious.
So why would you want one? Let's face it, you probably don't need one, your new camera lets you point it at any given scene and in full auto mode it takes a perfectly usable image. When shooting manual the in-camera meter readings are fast and reliable - you can even change between spot metering and full frame average metering depending on the situation, so you've got along just fine without one so far. Assuming then that your interest is piqued and you either want to revisit the old days, or just look into your first purchase, what should you look for in a handheld light meter? Whether to choose Reflective or Incedental will be completely down to personal choice but plenty of the modern digital light meters perform both functions such as the Sekonic L-308S Flashmate light meter at around £139 (pictured above).
If you decide to go for something a little older, you can find good examples for between £10 & £20 on ebay. My own light meter of choice is also a Sekonic - a model that stopped production around 1978, but needs no batteries, has no on/off switch and is incredibly easy to use (see picture below).
So don't be afraid of digging around car boot sales, as the old models perform the task in a beautifully simple fashion and whilst buying a light meter may not turn you into a pro overnight, hopefully this serves as a very brief introduction to a piece of equipment that previously have seen a bit daunting. Besides... as a photographer, you're always looking at scenes in your everyday life and thinking, "that's a 125th of a second at f/2.8 if I push it up to ISO800" and being able to refer to that little light meter you've taken to carrying around with you will let you know if you're right... or is that just me?