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Edit for clarity- The bulbs are not flickering or flashing. They periodically (> 10 minute intervals) turn off and then on in unison.
I have a chandelier with 5 bulbs. I recently replaced all 5 60w incandescent bulbs with 40w equivalent Philips LEDs. The chandelier is on a dimmer. The bulbs work fine but after about 10 or 15 minutes, all 5 bulbs blink once at the same time. Then there will be another long pause and it will happen again. Rinse. Repeat.
I thought it might be the dimmer which is about 25 years old so I replaced it with a new Leviton slider dimmer(LED compatible). The same thing just happened again. The only common element to the five bulbs is the dimmer switch, right? There are no electronics in the chandelier.
What else could cause them all to act in unison?