I would think more
IR light in the 850nm range would still help.
No, brightness is not the issue. It's lack of contrast. Below are a couple of the new plates, daytime and nighttime, from the same camera. At 850nm, the blue background and the white lettering have nearly the same reflectivity. You can see the plate just fine, but it's a white rectangle, with the characters unreadable by the LPR software 98% of the time.
I've talked to some people and I think I know what's going on. I was told that the new TN plates are specified for reflectivity at 740nm, which is the IR standard used in high-end LPR cameras for many years. The problem is that the pigments chosen for the new plates were not also tested at 850nm.
Supposedly the 740nm standard has been in place for years. The difference is that previous plates were also reflective at 850nm, but not by design, only serendipity. Unfortunately that's no longer true.
Any LPR camera that relies on 850nm IR illumination will be blind at night to a lot of TN and MS plates before the year is out. I've been told that Flock Safety is among those who are working to fix this issue with their own products. I suspect they'll be retrofitting a lot of cameras in the next few months.
And of course this also knocks out those of us who are using Dahua -Z12E varifocal cameras for DIY LPR. So I need to do some tests and see if 740nm illuminators will solve the problem.
