An LED unit includes an LED having a first optical axis and a transparent envelope receiving the LED therein. The envelope is a cylinder inclined towards a lateral side. The envelope includes two concave surfaces respectively defined at a top and a bottom thereof, and a convex surface formed on the top thereof. The two concave surfaces have the same second optical axis and the convex surface has a third optical axis. The second and third optical axes are parallel to each other and angled with the first optical axis. The second and third optical axes are inclined towards the same lateral side as that the envelope is inclined toward. The two concave surfaces and the convex surface are all aspheric.
