I have read here and there that new appliances will, or are, being built with like a transponder ID in them that identifies what it is by a factory ID. Electric oven fires up, it sends to the smart meter, "I am an electric oven, built by XXXX, max wattage is XXX. Same for other items. I am a TV, I am a dryer, I am a dishwasher.
This really won't mean much for a decade or two until all existing appliances wear out and need to replaced. After that, every electrical item could be ID'd with start and stop times. The question is will the ballast makers be forced to also include the transponder that says, "I am a MH or HPS light"...or not install anything and the meter could see it as an "Unidentifiable device"?
Oh yes the electrical transponders for the E-grid. I forgot about those. I thought they were mainly for high wattage appliances, like the fridge, stove, tv, and maybe computer. I did see a documentary where they talked about putting them in everything, with the wistful future look in their eyes.
So maybe one day it will all have ID's, but even if they don't, the wattage use signature can still be determined. It would also be really easy for an organization like the DEA to just buy one of every ballast on the market, test them themselves, and give out, or sell the data to other law enforcement agencies.
As of right now though, they can potentially ID everything in your house with clarity. My only ways to combat this, that I've thought of so far, run your veg 24 hours, use a flip flop relay to break up the budding into 2 rooms. This leaves a constant power signature, so they can only get data when the appliances turn on. So to mask that, I just turn off my main breaker, plug in all my lights, and flip it on. I assume the resulting storm of appliances drawing power will mask any signatures.