What does this equation mean?

That is a clean, falsifiable test in principle. In practice, computing L for the Photonic Fabric Module runs into a wall immediately, and the wall is worth describing precisely rather than waved past. B$W_{\text{opt}}$ is at least partially available — the module’s 7.2-terabit-per-second optical connectivity figure and the appliance’s 32-terabyte pooled capacity are both disclosed, even if the realized random-access figure specifically (as opposed to the module’s headline peak) is not. $P_{\text{opt}}$ is not available at all. Not in the chiplet-marketplace technical summary, not in Celestial AI’s own Hot Chips 2025 presentation, not anywhere on the corporate site that now forwards to Marvell’s. No wattage figure, no picojoule-per-bit figure, no energy-per-bit number of any kind appears anywhere in this fabric’s public technical record for either the switch ASIC, the optical links, or the module as a whole. That is not a gap this search failed to close through insufficient effort; it is an absence confirmed by checking the vendor’s own conference disclosure, its own product-summary coverage, and its acquirer’s public materials, and finding the same silence in all three.