Rather than satisfying every part of the crowd's question, Jesus tells them that the light will be with them only a little longer: 'Walk while ye have the light, lest darkness come upon you.'
The image combines everyday travel experience with John's larger theology of Jesus as Light.
Before artificial street lighting, daylight strongly governed safe travel and ordinary work. A traveler overtaken by darkness faced greater difficulty knowing the path and avoiding hazards. Biblical literature had long used light and darkness for revelation, righteousness, danger, and judgment. John has already identified Jesus as the Light of the World and described the conflict between light and darkness from the prologue onward.
The everyday image gives urgency to the theological claim. Opportunity to respond to Jesus is not presented as indefinitely postponable.
The crowd is asking for conceptual clarification, but Jesus presses for trust: while the Light is among them, they are to believe in the Light and become 'children of light.'