Taken in the received sense, hexagram 30 describes clarity, visibility and intelligence, and insists that all three are contingent.
That contingency is the reading's whole point. Fire is real while it has fuel. A person's brilliance, position or reputation is likewise sustained by something outside itself, and the hexagram's counsel is to attend to what is doing the sustaining rather than to the flame. Wilhelm's judgement advises care of the cow, an image usually read as the patient maintenance of what feeds the light.
In practice the figure reads for visibility and for attachment at once. It turns up for situations in which the querent is being seen, publicity, recognition, exposure, and the useful question it puts is what that visibility is resting on.
The second half of the reading is less comfortable. The third line has the sun setting, with an old person either singing or lamenting, and the alternatives are not consoling: without accepting the turn, one laments. The fourth line flares and is discarded. Fire in this hexagram is not a steady lamp; it is something that burns through its material and stops.
Both Wilhelm and Legge preserve that arc. Where they differ is in how much philosophical weight they put on it, and Wilhelm, reading through the later commentators, gets considerably more doctrine out of the figure than the line texts alone would yield. That is not a criticism of him so much as a description of what his translation is: a rendering of the I Ching as the later Chinese tradition understood it, which is a legitimate and valuable thing to have produced.