A mesh, frame or electrode array can collect droplets even with its power disconnected. Comparing an operating device only with empty space combines passive interception with everything electricity adds. That may describe total device performance, but it does not isolate the added value of switching the apparatus on.
In Weatherhill’s proposed protocol, C is the passive collector condition and D is the powered condition. The hardware, optical paths, inlet challenge and specified bulk flow are matched. The primary question is whether D reduces optical attenuation beyond the reduction already produced by C.
Normalize before comparing
Let R = βout / βin describe transmission of the incoming extinction burden through the apparatus. A useful relative effect is 1 − RD / RC. If the passive condition has RC = 0.80 and the powered condition has RD = 0.60, electrical operation produces a 25% reduction relative to the normalized passive output. These are illustrative numbers, not Weatherhill results.
Normalization does not remove every confounder. Upstream and downstream signals must refer to the same transported fog, with the appropriate transit lag. Changes in humidity, temperature, droplet population or flow can otherwise resemble treatment effects. Published FM-100 instrument evaluations also show why particle sampling and sizing require their own qualification.
Randomized order and adequate washout reduce the chance that drying, wetting or natural drift determines which condition wins. Repeated readings within one run improve the description of that run; they do not substitute for independent experimental days. Discovery measurements choose a setting. A separate, frozen confirmation phase tests it without continuing to optimize against the same observations.
Keep the interpretation attached to the comparison
Damak and Varanasi demonstrated electrical enhancement of fog collection. That establishes a relevant physical mechanism, but the proposed D/C test asks its own optical question. Even a successful D/C result would measure the combined consequences of powering the apparatus, including any local airflow changes. It would not automatically separate electrophoretic capture from mixing, evaporation or other mechanisms.
A credible pass would support an optical benefit for the selected apparatus, fog state and flow range. It would justify the next experiment. It would not, by itself, establish outdoor clearing, a useful service area, reliable operation or acceptable energy cost.