A light beam adjusting device comprising: a first adjusting unit and a second adjusting unit arranged side by side; wherein the first adjusting unit comprises: a first incident portion arranged to receive a first light beam; a first exit portion having a first light exit face; and a first light beam adjusting portion located between the first incident portion and the first exit portion and having at least one first deflecting face and at least one second deflecting face; and wherein the second adjusting unit comprises: a second incident portion arranged to receive a second light beam; a second exit portion having a second light exit face; and a second light beam adjusting portion located between the second incident portion and the second exit portion and having at least one third deflecting face and at least one fourth deflecting face, wherein the first deflecting face is arranged to deflect a part of the first light beam towards the fourth deflecting face, and the third deflecting face is arranged to deflect a part of the second light beam towards the second deflecting face, and the fourth deflecting face is arranged to deflect the part of the first light beam deflected by the first deflecting face towards the second exit portion to cause the part of the first light beam to be emitted from the second light exit face, and the second deflecting face is arranged to deflect the part of the second light beam deflected by the third deflecting face towards first exit portion to cause the part of the second light beam to be emitted from the first light exit face; characterized in that the first light beam adjusting portion comprises at least one first aperture having a first inner wall for forming the first deflecting face and a second inner wall for forming the second deflecting face; and the second light beam adjusting portion comprises at least one second aperture having a third inner wall for forming the third deflecting face and a fourth inner wall for forming the fourth deflecting face. a first adjusting unit and a second adjusting unit arranged side by side; wherein the first adjusting unit comprises: a first incident portion arranged to receive a first light beam; a first exit portion having a first light exit face; and a first light beam adjusting portion located between the first incident portion and the first exit portion and having at least one first deflecting face and at least one second deflecting face; and wherein the second adjusting unit comprises: a second incident portion arranged to receive a second light beam; a second exit portion having a second light exit face; and a second light beam adjusting portion located between the second incident portion and the second exit portion and having at least one third deflecting face and at least one fourth deflecting face, a first incident portion arranged to receive a first light beam; a first exit portion having a first light exit face; and a first light beam adjusting portion located between the first incident portion and the first exit portion and having at least one first deflecting face and at least one second deflecting face; and wherein the second adjusting unit comprises: a second incident portion arranged to receive a second light beam; a second exit portion having a second light exit face; and a second light beam adjusting portion located between the second incident portion and the second exit portion and having at least one third deflecting face and at least one fourth deflecting face, a second incident portion arranged to receive a second light beam; a second exit portion having a second light exit face; and a second light beam adjusting portion located between the second incident portion and the second exit portion and having at least one third deflecting face and at least one fourth deflecting face, wherein the first deflecting face is arranged to deflect a part of the first light beam towards the fourth deflecting face, and the third deflecting face is arranged to deflect a part of the second light beam towards the second deflecting face, and the fourth deflecting face is arranged to deflect the part of the first light beam deflected by the first deflecting face towards the second exit portion to cause the part of the first light beam to be emitted from the second light exit face, and the second deflecting face is arranged to deflect the part of the second light beam deflected by the third deflecting face towards first exit portion to cause the part of the second light beam to be emitted from the first light exit face; characterized in that the first light beam adjusting portion comprises at least one first aperture having a first inner wall for forming the first deflecting face and a second inner wall for forming the second deflecting face; and the second light beam adjusting portion comprises at least one second aperture having a third inner wall for forming the third deflecting face and a fourth inner wall for forming the fourth deflecting face.