Epson's Eco mode, of course, draws less power, puts up a less bright image, saves the environment, and reduces fan and overall projector noise. One could say it not only saves energy, but also reduces noise pollution (by 8 decibels).
The same roughly 37% measured power drop would be consistent, regardless of color mode. That is, expect the same 35-40% drop in Theatre, in Presentation, etc. BTW, figure most of our readings are within +5% when we measure.
||Percentage Drop In Brightness
Here's a brief story for you. Back in the mid and late '90's the big show then (and now) for business projectors was Infocomm, but back then, most projectors had a few hundred lumens. At the Infocomm show, 50 or so projectors would be all set up on the same screens for the annual Infocomm Shoot-out. The same content was fed, in a fully darkened room, to each projector so we could compare.
As best I recall, two teams were created to go through all the projectors and measure the brightness of all of them, and ultimately those measurements were posted. Both teams used identical equipment. Typically the differences though were 3-5% - just from "how" they measured, between team 1 and 2 with one team fairly consistently producing higher measurements, But the thing was, sometimes the team that was typically reporting lower numbers might be 5% or more higher on a one or two projectors.
In other words, one team might find projector A to measure 500 lumens, while projector B measured 470, but the other team might find projector A to measure 475, but projector B to measure 510. Go figure! And with the same equipment!