ILFORD '901' filter

Not seen one of these before - https://www.ebay.co.uk/itm/Ilford-D...677952?hash=item3da1360880:g:82YAAOSwwnpekypv - presumably only safe with graded papers?

That looks a lot like the kodak safelights I used long ago. They were the ones with small cup-shaped filters and you could change between the yellow-green and the dark green. They worked well and yes it was with graded papers only. The polycontrast filters of the day were deep amber and gave very little illumination.

Apparently only for contact speed papers etc.