This reflector is approx 8cm high and 5cm wide. He is very well made. On the back initially, the lid has to be removed, then 2 AAA batteries (not included) insert. So you can then 30h enjoy the light. The LED light is very bright and it seems far, very far. There are 2 buttons and LED LD. LD is for 2 spotlights down. With LED, you can choose from 3 different modes. Of course, a permanent lighting is. With the light you will certainly never be overlooked. The luminaire can easily be mounted to the bike (bracket included). Thanks to the guide rail on the back only the lamp must be done when changing batteries. Holder can remain on the bike. Light you can never have too much on the bike. Since these Patuoxun waterproof bike light is a good choice.