I guess everybody noticed spot patterns on older panels. Sometimes they appear as slightly brown colored spots or brighter spots that are usually accompanied with varnish layer peeling off .
These spots will appear above backlight lamps and are the consequence of lamp heat over time. In the worst cases you can get a panel with visible panel burns and thermal damage!
When searching for panel backlight lamps replacements I was careful to pick the right ones. After all I went through to get the genuine panels I didn’t want to make additional panel burns due to incorrect bulbs! On the underside of each Sirio panel there is actually a lamp part number written MS24367-715, (5V, 0.12A, 0.60W). I think the size of lamp is 3.2 x 6.5 mm.
I also talked with Phil (Simvionics) about panel burns and learned that Boeing panels have 60mA, 0.3W bulbs, that means they are half bright and half cooler. Same 60mA bulbs can also be found on A320 FIRE and ADIRS panels which are non Sirio panels. Hmm… I have never seen these two panels with spots or panel burns!