Does that light that comes on tell you the optimum to shift your manual car?

The shift light (when a car happens to be equipped with one) in 99% of cars is used as an indicator of when to upshift for maximum fuel economy. Typically under light loads the light turns on at low RPM to encourage the driver to upshift early for better economy. Very few cars past or present have an upshift light (from the factory anyway) to indicate when the engine is approaching redline, although a few do or did.