A medical instrument, comprising: a housing; and an end effector assembly (100, 200, 300) operably connected to the housing, the end effector assembly including: first and second jaw members (110,120, 210, 220, 310, 320) each having a proximal end (110a, 120a, 310a, 320a), a distal end (110b, 120b, 310b, 320b) and a tissue contacting surface (112,122, 212, 222, 312, 322), at least one of the first and second jaw members movable between a first, spaced-apart position and a second proximate position, wherein in the second position, the jaw members cooperate to define a cavity configured to receive tissue between the jaw members; and at least one light-emitting element (132, 232, 332) coupled to the first jaw member, the at least one light-emitting element adapted to deliver light energy to tissue grasped between the first and second jaw members to treat the tissue, characterized in that: a first longitudinally extending groove (130, 230, 330) is defined in the first jaw member and a second longitudinally extending groove (140, 240, 340) is defined in the second jaw member, wherein the first longitudinally extending groove is located opposite the second longitudinally extending groove when the jaw members are in the second position; the at least one light-emitting element (132, 232, 332) is disposed in the first longitudinally extending groove; and the second longitudinally extending groove has a reflective surface, whereby light emitted from the light-emitting element may pass through the tissue grasped between the first and second jaw members and be reflected back through the tissue. a housing; and an end effector assembly (100, 200, 300) operably connected to the housing, the end effector assembly including: first and second jaw members (110,120, 210, 220, 310, 320) each having a proximal end (110a, 120a, 310a, 320a), a distal end (110b, 120b, 310b, 320b) and a tissue contacting surface (112,122, 212, 222, 312, 322), at least one of the first and second jaw members movable between a first, spaced-apart position and a second proximate position, wherein in the second position, the jaw members cooperate to define a cavity configured to receive tissue between the jaw members; and at least one light-emitting element (132, 232, 332) coupled to the first jaw member, the at least one light-emitting element adapted to deliver light energy to tissue grasped between the first and second jaw members to treat the tissue, first and second jaw members (110,120, 210, 220, 310, 320) each having a proximal end (110a, 120a, 310a, 320a), a distal end (110b, 120b, 310b, 320b) and a tissue contacting surface (112,122, 212, 222, 312, 322), at least one of the first and second jaw members movable between a first, spaced-apart position and a second proximate position, wherein in the second position, the jaw members cooperate to define a cavity configured to receive tissue between the jaw members; and at least one light-emitting element (132, 232, 332) coupled to the first jaw member, the at least one light-emitting element adapted to deliver light energy to tissue grasped between the first and second jaw members to treat the tissue, characterized in that: a first longitudinally extending groove (130, 230, 330) is defined in the first jaw member and a second longitudinally extending groove (140, 240, 340) is defined in the second jaw member, wherein the first longitudinally extending groove is located opposite the second longitudinally extending groove when the jaw members are in the second position; the at least one light-emitting element (132, 232, 332) is disposed in the first longitudinally extending groove; and the second longitudinally extending groove has a reflective surface, whereby light emitted from the light-emitting element may pass through the tissue grasped between the first and second jaw members and be reflected back through the tissue. a first longitudinally extending groove (130, 230, 330) is defined in the first jaw member and a second longitudinally extending groove (140, 240, 340) is defined in the second jaw member, wherein the first longitudinally extending groove is located opposite the second longitudinally extending groove when the jaw members are in the second position; the at least one light-emitting element (132, 232, 332) is disposed in the first longitudinally extending groove; and the second longitudinally extending groove has a reflective surface, whereby light emitted from the light-emitting element may pass through the tissue grasped between the first and second jaw members and be reflected back through the tissue.