Indiana Construction Zone Speeding Ticket

[Flyerno12]

My question involves a traffic ticket from the state of: Indiana

Situation: Driving on I-65North on a Wednesday afternoon with a clear sunny day. Along the highway I see "Construction Zone" signs that also have a single light on top of them. I checked to see if the light was flashing or if there was any sign that said "Reduced speed when lights flashing", but there were neither. Furthermore, I did not see any construction workers present. Traffic was moving along around 70MPH as well. A cop was making a U-turn on the highway median as I passed and then pulled me over. He explained that I was speeding in a construction zone and I explained that I did not think the reduced speed was valid since the light was not flashing.

Net, he gives me a ticket for 72 in a 45 zone and I asked him if we stationary when he took my reading and he said yes (he wasn't), but then also proceeded to say that it does not matter if he is stationary or not. I am looking at a $450 dollar fine for this honest mis-interpretation of signage and am wondering how/if I can fight this.
I am open to going to court and possibly securing an attorney to help clear it up.

[flyingron]

If there are CONSTRUCTION ZONE signs, the zone is in effect. It doesn't need a flashing light. The light is purely to call your attention to the sign, not an indication whether the zone is active.
Being mistaken about what a sign means is not a defense.