The system in our shule is that whenever their is a chosson in shule there is a special light that is turned on so people know not to say tachanun. Now, today a chosson walked in and the light was on during shmoneh esrei, and towards the end of chazoras hashatz the light was off. (Assuming that everything is accurate and the chosson did in fact leave at that time).
Do we recite tachanun or not? Are their different opinions?
If the chosson left the shul during chazoras hashatz, it is controversial if they should say tachanun or not. There are those that say that that is what the chosson should do, while others say that the tzibbur will not have to say tachanun in any case.
Trumas Hadeshen Psakim 80, Eshel Avrohom (Butsatch) 131-4, Lekat Hakenach 131-31*. See Shlomo Tefilah 11-6,7 that R’ S. Z. used to tell the chazan when he was a sandak, so that the shul shouldn’t say tachanun, even though he could have walked out then.