The safest way is to test
Testing red light is easy and always reccomended where you buy a new lamp.
I test it with 2 or 3 strips of paper with a coin over them. I put the first at 50 cms of the lamp, the other at 1 meter and the other at 2 meters and expose to red light for 10 minutes.
If, after developing, coin is noticeable in the first one but no in the second, lamp safe from 1 meter of the source light; if neither of the test stips are fogged, lamp is VERY safe. If 2 or 3 test strips are fogged, you have to be very careful using the lamp with that paper.