If you look closely, you'll see it's actually in the shape of a reflector - usually a cone. Also not shown is that some higher-power leds use a blob of silicone

If you look closely, you'll see it's actually in the shape of a reflector - usually a cone. Also not shown is that some higher-power leds use a blob of silicone around the chip to protect the bond wire during thermal expansion -- the cone helps hold the silicone while curing.