Light projection assembly for opacity monitors

An opacity monitor, comprising:

• a retroreflector assembly;
• and
• a transceiver assembly configured to project an output light beam to the retroreflector assembly, wherein the retroreflector assembly is configured to reflect the projected output light beam back to the transceiver assembly as a return light beam when the transceiver assembly and the retroreflector assembly are optically aligned along a central axis, the transceiver assembly comprising:
• a sensor configured to detect an intensity of the reflected return light beam;
• and
• a light projection assembly, comprising:
• an integrating sphere defining an input aperture, an output aperture, and a spherical-shaped internal chamber;
• an LED source located external to the spherical-shaped internal chamber at the input aperture, wherein the LED source is configured to emit light through the input aperture into the spherical-shaped internal chamber;
• a light baffle surrounding a portion of the output aperture, wherein the light baffle extends into the spherical-shaped internal chamber to prevent light emitted by the LED source from exiting directly through the output aperture;
• and
• a condenser lens located external to the spherical-shaped internal chamber at the output aperture, wherein the condenser lens is configured to collect light reflected within the spherical-shaped internal chamber that exits through the output aperture;
• wherein the transceiver assembly is configured to use the collected light to produce the projected output light beam, and
• wherein opacity values measured by the opacity monitor vary by no greater than ±0.5% opacity when the transceiver assembly or the retroreflector assembly is angularly misaligned by up to ±0.25 degrees from the central axis at a distance of 3 meters between the transceiver assembly and the retroreflector assembly.