Light cone emiits smoke blast.It was emitting a cone shaped light that stopped in distance. The lit craft then emitted a smoke like substance that expanded out from the cone shaped light in a perfect circle. the cloud continued to grow in size until touching the ground and reaching hundreds of feet in the sky. we thought it was a nuclear blast but heard no sound. and the cloud was nowhere near bright enough. we reported it to our command but they said it was an illumination round. I have been a mortar man for 10 years and I know what illumination looks like and that was not even bright enough for that. It was pitch black outside and the sky was perfectly clear except for this object. after the smoke cloud dissipated about 5 min later the object was gone and the light cone had shifted into a cloud as well and dissipated about 3 min after the large one.