A document validator comprising a light pipe assembly comprising: a first light input port at a first end of the light pipe assembly ; a light emitting surface that extends substantially from the first end to a second end of the light pipe assembly ; a plurality of surface features (402, 404a-404c, 704a-704g) in the light emitting surface , wherein each surface feature (402, 404a-404c, 704a-704g) defines a first internally reflective boundary (650a-c, 654a-c) at a far end of the surface feature (402, 404a-404c, 704a-704g) relative to the first light input port , wherein light that enters the first input port is directed to the first internally reflective boundaries (650a-c, 654a-c); one or more reflective surfaces arranged to reflect light from the first internally reflective boundaries (650a-c, 654a-c) through the light emitting surface , wherein the first internally reflective boundaries (650a-c, 654a-c) vary in size across the light emitting surface ; and a second light input port at the second end of the light pipe assembly, wherein each surface feature (402, 404a-404c, 704a-704g) in the light emitting surface defines a second internally reflective boundary (650a-c, 654a-c) at a far end of the surface feature (402, 404a-404c, 704a-704g) relative to the second light input port , wherein light that enters the second light input port is directed to the second internally reflective boundaries (650a-c, 654a-c), wherein the one or more reflective surfaces reflect light from the second internally reflective boundaries (650a-c, 654a-c) through the light emitting surface , and wherein the second internally reflective boundaries (650a-c, 654a-c) vary in size across the light emitting surface . a first light input port at a first end of the light pipe assembly ; a light emitting surface that extends substantially from the first end to a second end of the light pipe assembly ; a plurality of surface features (402, 404a-404c, 704a-704g) in the light emitting surface , wherein each surface feature (402, 404a-404c, 704a-704g) defines a first internally reflective boundary (650a-c, 654a-c) at a far end of the surface feature (402, 404a-404c, 704a-704g) relative to the first light input port , wherein light that enters the first input port is directed to the first internally reflective boundaries (650a-c, 654a-c); one or more reflective surfaces arranged to reflect light from the first internally reflective boundaries (650a-c, 654a-c) through the light emitting surface , wherein the first internally reflective boundaries (650a-c, 654a-c) vary in size across the light emitting surface ; and a second light input port at the second end of the light pipe assembly, wherein each surface feature (402, 404a-404c, 704a-704g) in the light emitting surface defines a second internally reflective boundary (650a-c, 654a-c) at a far end of the surface feature (402, 404a-404c, 704a-704g) relative to the second light input port , wherein light that enters the second light input port is directed to the second internally reflective boundaries (650a-c, 654a-c), wherein the one or more reflective surfaces reflect light from the second internally reflective boundaries (650a-c, 654a-c) through the light emitting surface , and wherein the second internally reflective boundaries (650a-c, 654a-c) vary in size across the light emitting surface . <EOS>