In pitch black they're very visible unless you're going immediately from bright sunlight. With 5-10 mins of adjusting it's really something.

The photos on the site are definitely long exposure, but I'm pretty pleasantly surprised in person.

I live in the hills of the Bay Area and the light pollution is too great outside for them to be obviously bright unless it’s been a really nice weather day (the parts that are growing are the parts that glow which is fascinating!). Outside, you can tell they look different than other plants if you are told they are different and you really take the time to look. Inside with all the lights off, they definitely make you say WOW!. They’re similar to the old “Indiglo” watch faces of the 90’s. You will not be able to see them glowing even in dim room lighting, the lights must be off.

All that being said, I am still quite happy with them! They take effort to be observed, but that effort is rewarding since it is such a unique experience. It’s really neat to see a stem glowing one night, which indicates that the next night there will be a new bright flower bud. Also I get a huge kick out of doing everything I can to propagate them, since it is stupidly illegal to do so.

Edit: for something comparable that you are familiar with, I would say it would take 6-8 plants at the size they arrive at to make the equivalent amount of light as a single small tea candle.