Most folks don't note it as being dark. When you figure that clear double pane glass has a VT of around 80-82%, a VT of 66% isn't that much of an offset for all the benefit and energy savings.

Agree with WOW.

It seems like a big difference based on numbers... almost 20% less light. Seems like it would be darker. I may just go with it though since it seems most people advise it isn’t a big deal. I am planning white windows with window grids on a White House. Should I worry about the windows giving off a green or blue tint?

Low-e does have a bit of a greenish or silverish tint to it depending on the formulation.

I would recommend that you get a sample of the glass if you are at all concerned about it.

Absolutely get a sample and see for yourself. If you are at all particular about having a bright interior, you will notice a HUGE difference in light transmittance between regular glass and the low e. My low e glass darkens the room considerably (and as stated above they have a very greenish tint). I was shocked and pretty bummed when they were first installed, but my main living area faces south and also has windows on the east and west side of the rooms as well (so LOTS of sunshine streams in all day) so it’s not that big a deal. But for me, if my main living area faced north, it would be a defined issue and I would get glass that has the highest allowable VT possible. I have heard many say it’s no big deal and they don’t notice it. But for others it’s a huge issue because they are much more sensitive to a lack of light.

There have been several posts on this forum from people with windows with LoE366 instead of LoE272 reporting a tint on the windows and dark interiors. But from what you wrote, it doesn't sound like you have much choice in this.

If it were me, $200 would be a small amount compared to the tens of thousands that a house's windows cost. I would try to get the LoE272 on your north-facing windows at the least. A time delay of a couple weeks to make the windows order doesn't seem like much if you will be living in this house for years.

Do not think that Marvin's Lo366 glass is any different from Andersen's or Pella's or other large manufacturers'. All the large windows manufacturers get their glass from Cardinal Glass Industries. What differs among the windows manufacturers is how the windows are constructed and materials used other than the glass portion. But the glass will be the same among the manufacturers.