FWIW, every Starfleet ship in TNG glows to an equal, physicality-obscuring degree when she enters warp.
Perhaps the glow of warp entry is the sign of straining engines, and there is a special degree of strain involved in the rapid accelerations to warp seen in TNG (much more rapid than any of the TOS movement), but not in the gentler accelerations that follow the initial jump from STL to FTL.
Only uncrewed equipment and madmen would engage in constant strain, of course. This would explain not only the onscreen glow of photon torpedoes (a tradeoff between safety and speed, going fully in favor of the latter), but also the onscreen mysteries of tiny or ancient probes that seem to outperform the best starships of the corresponding era (things like Friendship 1 must be glowing like mad to cross quadrants, but this
always happens offscreen)!