Studies show that cyclists are chronically bad at estimating how visible they are on the road. This study, called “Cyclist Visibility at Night: Perceptions of Visibility Do Not Necessarily Match Reality” demonstrates that cyclists routinely overestimate their visibility by dozens of meters(!). The only consolation for our perceptions is that they tend to get better the more we ride, so more experienced cyclists are more accurate about their estimates of how well cars can see them. Bottom line: even if you think that car in the distance can see you, it probably can't. Keep that in mind when you're on the road.
Fluorescent or Hi-Visibility (hi-viz) colors can show off your flair and make you more visible during the day, but they aren’t going to suffice at night. The same study referenced above found that a cyclist in a fluorescent vest was only identified 15% of the time at night, while a cyclist in black was recognized only 2% of the time. While these colors might be bright enough to help motorists notice you during the daytime, people just don’t see color well at night. While that neon yellow vest might be better than wearing a dark color, it’s hardly a robust solution. In fact, the researchers even argued that wearing such colors has the potential to do more than good as “[C]yclists wearing fluorescent clothing may be at particular risk if they incorrectly believe themselves to be conspicuous to drivers at night.” So while fluorescent colors will help you be seen during the day time, they're a partial solution (at best) during night rides.
Dusk, or twilight, the time between about half an hour before sundown, and half an hour after sundown, is one of the most dangerous times to be on a bike because it’s the time of day during which our eyes are trying to switch between cones (which focus on color and are better suited for daytime) to rods (which focus on movement and are better suited for nighttime). This process, called adaptation, happens inside your eyes any time the light level changes. Around sundown, our ability to perceive color is compromised, but our eyes haven't fully adjusted to the low light conditions, making visibility bad. Unfortunately many urban cyclists and drivers experience a kind of perpetual twilight thanks to streetlights, headlights, and other lighting, so drivers may have difficulty seeing both color and movement. TL/DR: be even more cautious during the twilight hours, as they're the most dangerous time of day for cycling (and that's not even including the whole werewolf-vampire fiasco).
There’s a reason that the law in many states and countries require lights: it’s because they increase visibility dramatically. When you use a bike light it makes you easier to see for not just cars, but also for pedestrians and other cyclists. Reflectors depend on the headlights of cars to work, so if a car's headlights are malfunctioning, your reflector won't help a driver see you. There are several other reasons a reflector might not do its job, but the bottom line is that a light will always provide illumination, so it will be easier for all other road users to see you, and that's the best way for everyone on the road to stay safe.