I read this thread and thought I'd chime in. Although I haven't taken the time just now to look for any specific articles, I will provide with my expert opinion which has accumulated in my brain over the last near quarter century that I have been doing landscape lighting.
As is commonly known, a well designed landscape around a home does add value. Two comparably sized and equipped houses side by side, one has a nice well groomed landscape with quality landscaping, lush plantings and a thick green lawn - the other has basic builder installed foundation plants and a half green lawn, which one garners the better curb appeal and likely the better value?... Clearly the one with better landscaping. Now, take that same house with the nice landscaping and add nice lighting, the curb appeal and intrinsic value goes up some more.
Landscape lighting can also be an effective tool at selling a home, which in effect, also increases the value. About 15 years ago, I had a client who had a big fancy house and we did a lot of lighting. He built a new house and was moving but having trouble selling his house. I went and did a full lighting service, even cleaned the lanterns and put new 'candle' tubes. We took pictures of the property at night and they used a few of those pictures in their real estate advertising for the home. Home sold soon after. Did the lighting do it? Who knows.
When a homeowner sits down with an agent to create the listing for selling their home and they mention that the home features a professionally designed landscape lighting system, which will provide beauty, safety and security, my dime is on that the value of the home will be impacted. If even the perceived value, still some value increase.
I remember when we used to say that exterior improvements, ie, landscaping, had the potential to add up to double their cost to the property value. My spin on this to a potential client was that I once new a lady who spent 20 grand on window treatments but the new buyers didn't like them, so that investment didn't yield any return for the owner. In contrast, how can anyone argue with well designed and effective landscape lighting?
So to answer your original question, I'm guessing no one did a study on this to yield any concrete answers. However, this might be a good topic that the AOLP tackles. Polling real estate data and trying to see if there is a noticeable differential in selling prices of homes with or without landscape lighting. That task will not be easy however, because there would be so many variables in what kind of lighting, professional or DIY, etc. A good experiment would be to list a house with no lighting on the market. Have open houses day and night and take offers. Next, install a quality lighting system. Repeat your open houses by day and night, emphasizing the night one. Entertain offers and see if there's a higher trend for the landscape lighting house.
Logic and common sense would dictate that there is a upward value trend for homes with landscape lighting as opposed to without. When you come down to it, when we sell these systems, we use logic to dictate what to light, how to light it, and why light it, thus, using logic to suggest to our clients that their investment in landscape lighting will provide them with value added upon selling their home.
I've never had a client contact me telling of how their homes' value decreased because I put lighting in.