Please understand that the answer to your question is going to be subjective at best, because everyone up here has his or her personal favorites when it comes to lighthouses... That said, my own personal favorites, both of which are easily accessible from your route, would be:
#1 Portland Head Light Lighthouse at Fort Williams Park in Cape Elizabeth, just outside Portland. Classic structure, great setting, super photo ops. Commissioned by George Washington, it's the oldest continuously operating lighthouse on America's Atlantic coast. The lighthouse itself is not open to visitors (nor are the vast majority of lighthouses in Maine), but there is a nice, informative lighthouse museum at the base of the light (follow the path to the left around the keeper's house). It's open daily until the Friday after Columbus Day, and then open weekends until just before Christmas.
#2 The Nubble Light in Cape Neddick. You can't get to the lighthouse itself because it's on a island with no public access, but there's a nice local park/parking area that provides some great opportunities for photos....
Both of the above have websites which can be Googled for more info, driving directions etc.
If I were to list a couple of others for consideration, I guess they would be the Rockland Breakwater lighthouse at the end of Rockland's breakwater -- just off Rt 1, you get to it by hiking/climbing over the large rock boulders that make up the breakwater. In addition to the lighthouse, being at the end of the breakwater gives you a great chance for photos of ships or boats entering or leaving Rockland Harbor -- including the vessels of the Maine State Ferry Service..... and West Quoddy Head lighthouse in Lubec, marking the easternmost point in the Continental United States.... often photographed because of its red-and-white-stripes paint design....
Thank you for the information I will check out the websites,doubt it will be on the weekend we get there to check out the musuem but seeing the lighthouse will have to do.
Understand your disappointment over not seeing the museum, but haven't found anyone yet who didn't think the lighthouse alone wasn't well worth the trip...
Along with West Quoddy in Lubec, I would say make the trip to Campabello Island and hit East Quoddy Lighthouse as well.
You have to go through Lubec and enter into Canada to see it, but I feel it's a most amazing site. Tip - head out in low tide so you can walk to it, if you go at high tide you can only see it from the shore (and you might get stuck if you try to walk to it as the tide comes in).
The East Quoddy light sounds interesting !!
We are going into New Brunswick anyway so will look into visiting that lighthouse as it sounds unique to be able to walk out to the island.
thanks for your suggestion.