Lights on the front of the helmet are necessary only if the following two conditions are met:
1.You want to go riding in very low light conditions.
2.You do not have a light mounted on the bike to see where you are going.
Most cyclists will use an extra detachable light on the handlebars to light their way because these are usually brighter and long-lasting. The LED lights on the rear of the helmet are enough to keep you visible to others.