To be able to give you some advice about backbox glare it would be of help if you could
tell us.
1. Which machine is affected ? TSPP, SP or TZ ?
2. Do you use LEDs in your backbox or regular bulbs ?
3. Do you prefer darker rooms while playing or lighter ?
4. Is your machine (this one you're talking about) in a darkened room ?
Possible solutions without having answers on above questions:
1. Use regular light bulbs for backbox lighting instead of LEDs to reduce
lumen strength if LEDs are in use
2. If you use a machine (Stern) with a fluorescend light tube then remove it
or the starter (it's easier) to test it without a lit backbox. It makes a huge difference
in dark rooms
3. Switch off backbox lighting in general to see the difference
I know that those solutions will cause some answers like "...I love the backbox lighting and effects and I will never switch it off...", but it's worth a try or you try playing in more lightend rooms.
Glare-free, non-glare or PDI glass won't reduce backbox glare in dark rooms successfully
but it will enhance the visibility in lightend rooms and reduce the glare to the better.
bibi,
Roman