After selling your streetlamps to cities far and wide, you have decided that your lamps won't be supported anymore, and their critical control software won't even be updated for security issues.

Instead of leaving them unsafe to use, you need to make it so the buyer can continue to use them safely, even though the light output may be reduced or they might not be as cutting-edge (eye-friendly wavelength, for example) as your new offerings.

Everyone is free to update to the new lamps if they want to, but there should be no artificial reason to force them to do so.