ECO or PWR Mode??

Calling any Prius brainiac that cares to chime in...
I have a simple question and a suspicion and wondered if anyone would care to elaborate their thoughts. Here goes:

When one presses the PWR button on the console, the PWR light comes on and the vehicle drives with great vim, vigor, and gusto. Similarly, when one presses the ECO button, the ECO light comes on and the vehicle drives a bit more subdued, for the purposes of increasing mpg and reducing ones carbon foot print. Way cool.

But, on a couple occasions, and I cannot tell you how it got into this mode, but I've noticed while driving along for a while, that all the operating mode lights are off (PWR, ECO, and of course, EV). The vehicle drives fine, perhaps with a bit of gusto and I've noticed my instantaneous mpg is lower that it would be in ECO mode, so it is obvious to me it is not operating in ECO mode. For the sake of the argument, I shall call this in-between mode, my "Ether" mode. But my question to anyone who would care to chime in is, in this condition, is the vehicle operating in PWR mode or somewhere between PWR and ECO? The only way for me to answer my own question definitively is to drive a specific route at a specific time of day (or at a specific outdoor temperature) in each of the 3 modes and note the mpg. Then doe this again in this 'Ether' mode and see where it ends up. But, for the sake of brevity, I wondered if anyone would care to guess or explain.

Thanks!

 

Thanks all.

I couldn't find my answer in the manual... but now it all makes sense.