here's the quote from the Portra/Supra tech pub:

Using a safelight will affect your results. If absolutely
necessary, you can use a safelight equipped with a KODAK
13 Safelight Filter (amber) with a 7 1/2-watt bulb. Keep the
safelight at least 1.2 metres (4 feet) from the paper. Keep
safelight exposure as short as possible. Run tests to
determine that safelight use gives acceptable results for
your application