Several options exist for making sure you’re visible in the dark. Foremost among them: clothing with Illuminite, a reflective fabric that has millions of mirror-like particles embedded between its threads. When struck by a light sourcea car headlight, for instancethe wearer appears to light up. It’s very effective; I use an Illuminite jacket for some nighttime bicycle riding. A very useful accessory for a runner might be the Microweave Vest ($60), a piece that can be worn over other clothing in a wide range of temperature conditions. Illuminite can also be found in insulating layers, if you want to wear something like a long-sleeve turtleneck as your main piece, with perhaps a non-reflective vest over that.
An inexpensive option is to buy a straightforward reflective vest and put that over your regular running jacket, shirt, or whatever. The Nathan Reflective Vest ($20) is that very animalit’s extremely light, fits over just about anything, and has vertical and horizontal reflective stripes for ample illumination. Works very well.
The third choice is to use one of the above AND add a blinking light. Roadrunner Sports, among other places, sells armbands for $17 that have LED lights attached. That makes you actively visible from a great distance, regardless of whether or not a car’s headlights are aimed at you.
And of course, it always makes the most sense to simply assume nobody sees you, and act accordingly. Run against trafficnot with itbe cautious, and obey all crosswalk laws. That’ll keep you running in safety.