I haven't seen the mogul three way incandescent bulbs in stores for around a couple years here. The medium three ways I still see in incadescent and LED. I think some grocery stores still stock them in incandescent too.

I suppose smaller hardware stores and lighting specialist retailers would still have the mogul three way bulbs though. It's a shame there's no drop in option for mogul three way aside from the original 100-200-300w lamp too, you can even use a medium adapter without losing the three way option.

I have noticed lately, especially that the 3 way mogul bulbs are not as easy to find as they once were. Lowes used to sell the Sylvania brand and then GE but a year or two ago, they stopped selling them and they ended up at Habitat. (Since sold out, so I guess somebody has a use for them). I do still see them available at Ace Hardware stores, but the big box stores have stopped selling them it seems for the most part.

Not only that, but even medium base 3 way is getting less common too. Lowes has them but I did not see them at Home Depot or Walmart anymore.

It's not getting to where though 3 way lamps are sold yet the bulbs for them are getting difficult to find in the same store.
LED versions are available I guess but also not easy to find, and in many cases the bulb would cost more than the lamp.

The first purple-shifted LEDs I've seen were retrofit kits that I don't know the manufacture of, in some park lights that were formerly HID. They actually did well when they were all working (not sure exactly when they were installed) but last year, it seems like they all got worse with some completely out, one flashing, and a few turning dim and purple and of course, all of them were replaced shortly after with new LED retrofit lamps.

The early CFL's were expensive to make and not that mass produced, not justifying the wider color tone offerings. So only the warm white (2700 or 3000K), the daylight 5000/5500K and for the east markets (where the very high CCT was or maybe even still is seen as a kind of noble luxury) the really cold 6500..7000K. That means 3 color tones, quite enough for (at that time) non mainstream product...

Haven't seen any go purple, but I have seen plenty turn that yellow-green color.

If you want to take pictures of HID lamps during operation, then I strongly advise you to buy a neutral density filter to protect your camera sensor and to slow the shutter time down so you don't get those ugly bright-and-dark stripes in the output pictures. As far as cameras are concerned, those in current cell phones are now good enough for most photography. Just make sure your front lens is clean and that you use the "pro" mode in your app where you can control key parameters such as ISO setting, shutter time, white balance and exposure compensation... everything you need to get the results you want.

Also, you'll have to learn how to use your camera properly, because auto modes are more likely than not to screw with the rendering (like mercury lamps turning green). So, spend time learning about photography if you don't know anything about it already (yes, there's work involved), there's plenty of great resources available online for beginners.

I’ve never taken a picture of a high pressure arc, but have viewed them through two pairs of sunglasses!, with today’s iPhone cameras that are pretty good, I suppose you could try it that way, but have the camera behind the sunglasses?
Saying that I think I do have a photo of a 400 watt mercury arc taken behind a dark screen?

I've done that, but the glasses colour the resulting image too much, not sure of the best method TBH 

Great job compiling all those videos into one place. I honestly think staring out the car window watching the SOX lights on the Gardiner was one of the things that got me into lighting. I remember being annoyed when the section from Humber to Dufferin got replaced with HPS back in '97. The CBC segment and the Global Night Ride/Night Walk segments are the main ones online but there's a few cameos in some music videos shot during that era.

https://www.youtube.com/watch?v=anfjynZ-lPc
(Mostly around the Inglis sign, with a couple shots of the Bloor HPS M-400As)

https://www.youtube.com/watch?v=V7_fdU7kUBI
Daytime shot of DVP SOX

Speaking of daytime shots there's a few of those floating around on YouTube.

https://www.youtube.com/watch?v=kEKY1-CGa_U
https://www.youtube.com/watch?v=xkwLKcUfpmc
1988 - Heading into Toronto from the west. This was the exact view I saw (starting at :50) when I was a kid heading into Toronto.

https://www.youtube.com/watch?v=Yc1xA27kxTg
1990 - showing the original on ramp from Leslie (For those not familiar with the Gardiner, the stub from DVP to Leslie was part of a cancelled portion intended to connect to the 401, hence the unfinished appearance)

https://www.youtube.com/watch?v=LLXqdhNuNv0
1994

https://www.youtube.com/watch?v=2PrlN50VSns
2000 - Leslie ramp just prior to demolition

https://www.youtube.com/watch?v=oRDn0NAMH6M
https://www.youtube.com/watch?v=yf4b4X4VeP0
2001 - showing the demolition of the original Leslie stub

https://www.youtube.com/watch?v=iAsgEq1tzYI
2001 - showing the new ramp at Carlaw post stub demolition. "New" ramp removed in summer 2021.

In terms of stills, there's a few on the Toronto City Archives, I posted one here a while back.

Even the "pre SOX" era on the Gardiner was pretty neat too. The ramps all had continuous fluorescent lighting in the railings but they were all removed over the years. Interestingly a small section of the luminaires are still there but no longer work. 

It depends on what camera you have. If you have a camera that allows for manual exposure and external lens filters (DSLR and some compact point and shoots) you can look into changing the exposure settings to get a clear picture of a arc. Depending on the arc, ND (Neutral Density) filters would also help.

For cameras such as cell phone cameras, you could try turning down the exposure value but I find that doesn't yield as good results as with using filters or using a small aperture.

The easiest way to learn is to just grab your camera, light a lamp, and play around with the settings and take note of which ones yield good results.

Never seen any LED street lighting fixtures do it here yet, but I’ve seen Lena Lightings ‘Codar’ battens colour shift to a purple colour within two years of installation!
I’m also starting to see Ansell Tornado Pros now starting to turn a blue colour!