Are OEM hi/lo driving beam patterns spot or flood?

They seem to a have a definitive cut-off at the top, but spill on the sides like a flood...

 

Flood and spot don't really apply to headlamp beam patterns. Not really useful to try and define lo/hi as either.

 

The short answer to your question is that OEM headlight beam patterns are regulated by the federal government. Said another way, whatever headlights OEM manufacturers (and aftermarket lighting suppliers) build must comply with specific federal standards. "Spot" and "flood" are not approved beam patterns for headlights. (Auxiliary lights are a whole different ball game.) In fact, what constitutes a spot or flood - as well as a number of other beam patterns - is not very well defined and vary considerably from manufacturer to manufacturer.

 

I've posted this before, over in the SAEJ581 driving light thread. This is an example of the various "test points" that are used to check the compliance of a manufacturers headlights. The basic idea is that there really is no such thing as a lowbeam "beam pattern," rather, there is a range of intensities between a minimum and maximum at various points in front of the lamp that a lamp must illuminate (or not). This is why there is such a broad range of performance between absolutely atrocious (meeting the legal minimums across the board) and high performance (not necessarily maxing all points).

A sharp cutoff across the horizontal spread of the top edge of the light is not necessarily indicative of a "good" low beam, either. This is something that is often touted as some sign of good/effective design, but in reality having such a harsh transition between light and dark can actually he a net negative for both the driver and oncoming/surrounding traffic. It may appear the driver is flashing his highbeams with each and every bump in the road, and it reduces the d4ivers ability to see past the reach of the lowbeams. It is also not proof of good glare control. In Crashnburn80's 3rd gen headlight test thread, he has some tests of a 5th gen 4runner LED projector lowbeam which has a small, but noticeable "deadspot/drop" in the beam pattern below the cutoff. This is an example of glare control for oncoming drivers, despite the fact the lamp has adequate light above the horizontal cutoff. It is intended to reduce the intensity of light reflected up off a wet road aurface into oncoming drivers windshields. You won't see things like that in a lot of aftermarket headlamps/retrofit attempts (but I'm getting off topic)

Sorry, I know my first response was a bit lacking in detail.