There are two types of lighting in cycling - lights to see the road, and lights to be seen by.
The first type are great for nighttime riding in areas of poor illumination, or where you might need to pick out potholes, road signs etc. They're not so good for being seen from the side, for example as you approach a side road or junction. Road users will rely on the light being at the right angle to see you. Not always a problem but the more we can do to help others see us, the better.
You can get around this by using lights that have a deeper illuminated surface, or a cut-away section. These present lighting to the sides giving a 180 degree illumination.