Not sure exactly how much time you have to spend, Carol.
I'd say the Belle Isle visit would be an easy one from almost anywhere in the Greater Detroit Area. Again, check the map I linked above. There are several lighthouses long the shore that you could view.
The trip to Port Huron from downtown Detroit via I-94 would take about 50-60 minutes one way. Then the travel time from Port Huron to Pointe Aux Barques at the tip of the "Thumb" would be about 4 hours round trip. Add on time for each stop. It could be a very nice one day trip.
Use the Internet Index of Lighthouse Links - Michigan page and research the opening times for these lighthouses:
Lightship Huron - should be open some hours every day. Very interesting to tour the whole ship
Ft. Gratiot - Generally only open on special days, But Bob Hanford, the 'keeper' might open it up and give you a tour with advance arrangements. email me and I'll give you his phone number.
Port Sanilac - private residence, no tours, but easily photographed.
Drive up the shore farther to Harbor Beach. No access, photograph from the pier at the harbor. But on your way into Harbour Beach, watch for the tiny town of "White Rock". Someone has built their 'dream lighthouse' on the West side of the highway. Again, private, but you can get photos of it from the road.
Next stop Pointe Aux Barques. As Dave said, it's in a park and is open for touring. From there, continue on around the Thumb at least to Harbour City - a restored village to which the Pointe Aux Barques Lifesaving Station was moved. 'Museum' has hours.
If you want to contine around the Thumb a bit more, you'll come to Port Austin. This has an off-shore lighthouse that you'll need a telephoto lens for -- or you might be able to hire a small boat for a trip out the lighthouse, depending on the weather.
You'll backtrack along the Lakeshore to Port Huron and pick up I-94 to Detroit for the return.
There are county roads that would avoid the more crowed shore highway. Check a Michigan Map.
Here's a report on my trip 'around the Thumb'
[This message has been edited by JChidester (edited 07-19-2001).]