Me too and not just for aesthetic purpose, flux can vaporise and fog the lens, with CSP LEDs (e.g. E21A) it can get onto the led via capillary action and damage it.
General electronics/smd “no-clean” is fine…there are some types that you want to avoid, though (water-based and acidic no-clean types). The no-clean part is really more about commercial high-volume soldering than it is single joints and small projects on a “larger” scale like we’re doing in flashlights. I just use good old fashioned liquid RMA from Kester and have a couple tubes of cheap and mid-quality paste for convenience at times. I’ve used the Kester no-clean liquid (can’t recall the part # now) and it was fine, seemed to be gentler and disappear faster but that may have been my technique back then. When you start doing lots of legs and closely spaced pins and such that’s when you need to be a bit more careful in product choice and application…for emitters and wires and most of the smd components we use, it’s fine to use what you have so long as it is safe for electronics (i.e. no plumbing or welding fluxes, even if cleaned afterwards). Flux is certainly your friend, though, and even the better flux-core solder wire often falls a little short in flux content…a tiny bit of flux rather than a tiny bit of new solder with flux in it will often solve little issues much more easily and not create new issues.
I clean up all flux residue whether I can see it or not. Most especially on the emitter dome/surface but I like to get rid of all of it even though leaving it there is usually fine. Even the no-clean can smoke up under heat if there is enough residue in a spot…like to prevent that if possible so lens cleaning (or reflector fouling) is avoided or minimized.
As an aside, I picked up a couple types of these “q-tips” a few years ago and love them. They’re a thin poly mesh covering on the tips, not foam or cotton, and they are so much better for a little aggressive scrubbing in flux removal…and no fuzzies left behind like with cotton q-tips, no snagging on components or solder spatter or burs. The plastic tube core can be smashed to change its shape a little if need be, and they make a few different tip shapes as well. These also don’t hold a lot of IPA/solvent like a q-tip does, which can be helpful. Gentle enough to be used on emitter domes so long as you are also gentle.
https://www.amazon.com/Cleanroom-Microfiber-Electronics-Semiconductor-Instrument/dp/B07GBGM6V2/
Bought this set soldering set https://www.amazon.com/gp/product/B003TC8EQS/
The solder paste works with the heat gun. Otherwise I’d stick to a very hot 380ish C tip and keep it coated and clean using a bar of sal almaniac. Rosin core solder and clean up any messes with a roll of copper wick. I don’t use copper to clean the iron. The bar works, can’t solder without it anymore. I think there’s other brands out there too.
Anyways gl!
Oh yeah the flux as mentioned too. Rosin flux comes in a tub works good.
Ammonium chloride products (blocks, bars, pastes) are best as a last resort for cleaning an abused tip that won’t clean up with normal flux and wiping (sponge, pad, wire pad) and refuses to tin evenly anymore. It’s quite aggressive and slightly abrasive so if used solely or regularly it can wear out tips faster. Best to let mild flux do the work with wiping and a protective coating of fresh solder for storage, and use the ammonium only when necessary (and this is cheaper, too). Fumes from the vaporized ammonium chloride are pretty nasty, too…keep them out of the sniffer and lungs if possible.
I have same tip been using forever. It’s even bent from the heat 
Yeah with you on fumes but work at a station I built, have an adjustable fan inside a dryer tube that sucks the fumes up and out the house while soldering. I really like the block because I like having a very hot tip. The thing with working on boards, especially emitters like the op, and especially if they’re mounted- the aluminum/copper frame absorbs heat. Run a hot hot iron. There’s other solder bars out there too but haven’t tried them.
I guess if you have no way to control the fumes but it works well. Also have a jewelers vise, little better for some work than helping hands.