After knowing that ring lights are very popular in filming and photography, seeing descriptions for circline fluorescent lamps being translated as “ring lights”; I am beginning to wonder if high CRI circline fluorescent lamps can function just like normal “ring lights” used in filming and photography.

So far, I have found this example of a circline fluorescent lamp being used as a “ring light”:

https://youtu.be/hnsmHkX5bbI?si=x5D_-qPAj9PREs4v

Why not? But not all phosphors are good for color capture. With digital sensor, color shifts can be generally cancelled, but there are still some small problems with metamerism and color saturation for critical shooting. High CRI probably will work mostly OK.




 

I was concerned that halophosphate circline lamps would make photos ugly.

Not partuculary ugly, but reds/blues may come out undersaturated.

Yes, they work fine. I made one for my mom and used an FC8T9/CW lamp as one. I just put it in a small adjustable desk lamp, and faced it backwards so that the gear wasn't showing and it looked more attractive.

Wouldn't use any form of fluorescents for photography ever.
I remember back in the days of CFLs that it was very hard to get a neutral tone to the pictures i took. Even in 82 CRI lamps, the green mercury emission line is noticeable in pictures. You can edit it out partially, but it is always better to take quality pictures than to have to edit everything afterwards.
Furthermore, you can run into significant rolling shutter effects due to the flicker inherent in AC driven fluorescents. You're much better off with some LED ring light, that matches the color temperature of your main lights.

But with a real camera (not mobile crap) one can always set a shutter time of 1/50+ s and longer, avoiding flicker and banding completely.
I agree that 2700-3000K rare earth may be not a good choice for a shooting lamp, paradoxically good ol' halo will be better.

I use a 22w to light up a work area for my makeshift macroscope for soldering jobs.
The 2700k ones aren't good, but I found the 4100k ones work decently.
If you need 60fps, then you'll need a good electronic ballast. Otherwise for filmic 24fps or TV 30fps, a magnetic will be fine.

Digital isn't a problem, the camera usually corrects fine. But if shooting 35mm film, it's difficult to avoid the green with most daylight balanced films.

Additionally, I am also pretty sure that lamps driven on electronic ballasts would also have a reduced flicker effect.

Depends on the ballast quality. Some electronic ballasts flicker rather wildly. Cheap ones may save on input smoothing capacitors, and even ones better made may still have have a few percents of flicker remaining, showing up on crappy cameras.

Not just on crappy cameras. Flicker is a matter of light variations that happen during a shutter speed that is considerably longer than one flicker period. If you have a shutter speed of 1/50s and a 50hz mains, it will flicker 100 times per second and you'll have one or two dark bands in the image. Cameras cannot compensate for this.

When making videos, things get even more complicated with not just shutter speed, but also frame rate becoming a factor. In general if you use a 50hz frame rate you're not gonna have that much trouble.

That goes right to the crappy cameras, sorry. Cameras that implement a cheap rolling shutter scan, where different parts of the frame are integrated/sampled at different times.

A proper camera, still or video, has so called global shutter, meaning light all over the frame is integrated for the time set as "shutter time", then integration is stopped and values from the pixels are transferred to A/D converter. That way even we have a shutter set at 1/100 or 1/120 in 60Hz world, we won't have banding most of the time, if the lamp does not rectify significantly.

My brain was stuck with phones for a bit, forgetting about standard stills cameras.
Still, it's a deficiency in the lighting. Camera lighting should not flicker. Many people do not even have a separate camera anymore.
In about half the pictures in the gallery here you can see the rolling shutter bands, if people take photos of lit fluorescents. All of those people would have a chance of encountering the same issue with circline ring lights.

LEDs can run on perfectly smoothed DC, while you can't realistically do that with fluorescents because you need a big resistive ballast and a way to ignite the tube, as well as a safe guaranteed break before make switch to swap polarity each time you fire it up.

HF drivers can help, but you only know if a HF driver is properly smoothed when you try it. The philips warm start driver in my 2x 20w fixture isn't, for instance. My 2x 36w osram - is.

If you want a good ring light, get some 2700+4000k (so you can adjust them to your main lighting) 96 CRI led strips or "neon" strips. That way you're guaranteed that your lamp will work with all phones and other cameras, not with only a subset of them.
One meter of the good stuff costs about 10 euro, and some basic LM317 linear drivers another 10 euro or so.

All that said, you can use low CRI lamps for artistic effect. Under warm white halophosphate light, you can get a desaturated, almost sepia effect that takes quite some effort to match with post processing. Any picture i take of my greyish brown cat come out looking absolutely spectacular under such light, as if she's living in an old book that has been untouched in a library for decades.   
But you need to do that stuff intentionally, as you don't want to have to fool around in post processing to make a vivid portrait-style picture from something that lacks color.
And while a fluorescent ring light will not completely not work as a ring light, it would not be as objectively good, or as universal in use, as one made with LEDs. By all means do it for fun, but do expect annoyances that may or may not pop up depending on your exact use case.
But if you do, go all the way. Use some overdriven halogens as ballast, rectify it, and as background lights, and device a nice polarity switching circuit with a latching relay that flips each time you start it up or something. Do put in a proper fast fuse, DC can easily draw arcs in a EOL halogen lamp!

Additionally, I also found another example of a circline fluorescent lamp being used as a “ring light” as well.

see here:

https://youtu.be/f2wgnVDAse0?si=Us9jH9pKDT2ULsGm

You know, if it's one thing, this thread did make me want to cross off another thing from my bucket list: manual preheat a circline.
FC8T9, some Satco tube. Wiring job, not recommended. Advance lc-14-20, despite the factor it drove it brighter than I expected.
Need one 4pin connector, eventually... But will strap to some cameras when the wiring's good to give it a try with a wider range of cameras.

https://1drv.ms/v/c/cfbafe3c4408f0ac/EQ0ln9z4SytJke4M4-qEESABoDnBVoEdNeg3GhdM-pN-yw?e=WhoOgw