Please clean the filter
In case you need to replace the filters in your projectors.
Recently I had a number of 'filterless' InFocus projectors become dysfunctional all at a similar time (what is that all about - an internal obsolescence clock that tells the projector to stop working?) 3 out of 4 projectors malfunctioning at a similar time with only a fraction of bulb hours used. My alternative was a turn to some older NEC projectors as a back up. When testing these, one would turn on and then off after a couple of minutes and another displayed the "Please clean the filter" message. It appeared to be time to check the filters. When I removed the filter cartridge on one there was no filter material and on the other the filter material disintegrated (this is not unusual for filter foam). However, I needed these machines to be up and running in the next day and there was no supplier for replacement projector filter foam locally. The only supplier of NEC filters was through Amazon, and that would take over a week to ship from somewhere overseas. The cost for 'branded' NEC filter foam at the lowest price was US$13 plus postage. I needed an alternative urgently. What I found was a local electronics supplier of a 'plastic fan guard kit' for less than half the price, that had a larger sheet of exactly the same filter foam loosely enclosed between two halves of the plastic guard.
Now the old NEC projectors are running smoothly again, and I have excess filter foam for a couple of other projectors.