Light Up The Night: While it is certainly very important to see where you are going when riding a bicycle at night, it’s even more vital to make sure other people, particularly motorists, can see you. Many bikes come with reflectors on the pedals and the wheels, and often the front and rear as well. But reflectors only work when car headlights reflect directly off of them (that’s why they are called reflectors), so on a dark street a bike with only reflectors is pretty much invisible. To make yourself more visible in all light conditions, it’s a good idea (and the law in Massachusetts) to add a white headlight to your bike, and a rear red light is far better than the tiny reflectors on most bikes. It doesn’t matter whether the lights blink or not, so get whatever style you like. If you don’t have pedal reflectors, the law also requires reflective ankle straps. And the law also requires that you be visible from the side, so if you don’t have wheel reflectors, wear a reflective vest or jacket, stick some reflectors on your messenger bag or pack, wrap yourself in holiday lights, or whatever else makes you visible.
Sound like a lot of stuff? Go minimalist with front and rear lights and something reflective (or least light-colored) on you. Just avoid the bike-ninja-dark-clothing-no-lights look!
- Bicyclists riding at night must have a white front light, and a red rear light or reflector
During the period from one-half hour after sunset to one-half hour before sunrise, the operator shall display to the front of his bicycle a lamp emitting a white light visible from a distance of at least five hundred feet, and to the rear of said bicycle either a lamp emitting a red light, or a red reflector visible for not less than six hundred feet when directly in front of lawful lower beams of headlamps on a motor vehicle. A generator powered lamp which emits light only when the bicycle is moving shall meet the requirements of this clause. MGL chapter 85, section 11B(8) http://www.mass.gov/legis/laws/mgl/85-11b.htm
- Bicyclists riding at night must also have pedal reflectors or reflective ankle straps, and reflectors or reflective material visible from the sides
During the period from one-half hour after sunset to one-half hour before sunrise, the operator shall display on each pedal of his bicycle a reflector, or around each of his ankles reflective material visible from the front and rear for a distance of six hundred feet, and reflectors or reflective material, either on said bicycle or on the person of the operator, visible on each side for a distance of six hundred feet, when directly in front of lawful lower beams of headlamps of a motor vehicle. MGL chapter 85, section 11B(9) http://www.mass.gov/legis/laws/mgl/85-11b.htm
- Bicyclists riding at night can add as many lights or reflectors as they want
This clause shall not prohibit a bicycle or its operator to be equipped with lights or reflectors in addition to those required by clauses (8) and (9). MGL chapter 85, section 11B(9) http://www.mass.gov/legis/laws/mgl/85-11b.htm

I’ve gotten into the habit of using both my headlight & rear light in blink mode during the day – you’re much more visible to motorists (especially in bad weather). It’s not just a matter of being seen – you have to be noticed.
Lights should be required 1/2 hour before sunset rather than 1/2 hour after sunset. It is scary how many cyclist ride without lights, reflective clothing, or a helmet. How come helmets are not reflective?