Purplish xenon color, and than LPS orange color.

What color do regular HPS lamps start up with?

Mercury free HPS lamps can cycle, but rarely. Have much yellower color than standard HPS lamp.
High xenon pressure HPS lamps can cycle, but rarely. Runs up much faster than regular HPS lamp.
Unsaturated HPS lamps are the non-cycling HPS lamp. Runs up bluish mercury. have stable voltage over life.
Regular HPS lamps can cycle.
I think that European HPS lamps aren't compatible with CWA ballast for HPS lamps as well.

Al is better conductor per weight (measured as resistance of given length of wire with each of such thickness so both have the same weight; because Al has about 3.3x lower density, for the same mass it will be 3.3x thicker cross section, so even with about 1.6x higher specific resistivity it yields about 2x lower resistance of that wire), not dimension (cross section).
Because with ballast what matters is the volume, not weight, because that dictates how heavy the core would be (larger volume for the winding means taller the ballast core legs, so more steel in them, so the total weight or cost saving won't offset the larger ballast size).
But some ballasts were made using aluminum wire, mainly US HX and CWA's, the calculation probably made it seem worth.
The main problem with AL for winding I would see the inherent fragility of the Al wire, moreover when that thin, resulting into reliability problems. And these problems then are not worth the savings, even if those were real.

Just searched the message boards and there is a lot of contradicting information. I have heard of the following HPS lamp types, some of which have been claimed to have non-cycling behavior:
- Mercury Free HPS
- High xenon pressure HPS
- Unsaturated HPS
- Regular HPS

What are the characteristics of these lamps? Which ones cycle and which ones don't? How do I identify them?

All of the HPS street lights near me are mercury-blue colored when they first strike, but my Ignitron lamp is white when it strikes. So obviously there are at least two types of HPS that are distiguishable by startup behavior.

What are these lamps marketed as? I have heard of Philips Alto non-cycling HPS lamps, what category do they fall under? Never knew there were so many different types.

Are unsaturated lamps ever used outside of retrofit lamps?

Also do these lamps have anything to do with the whole HPS CWA compatibility mystery? (they say that saturated HPS retrofit lamps are incompatible with CWA MV ballasts, yet HPS CWA ballasts exist)

Thanks!

Something was rubbing against it...

What caused them?

It is true, the aluminum is more than double the conductivity of copper per conductor weight (not cross section, really weight), also way cheaper, but these aspects are not that significant on thinner wires. There the surrounding accessory (the insulation, restriction to the cable assembly materials to prevent corrosion, more care so more expense needed for termination,...) either cost the same or even is more expensive with aluminum, so if the material/weight savings are not substantial, it does not make much sense.

Regardless of the exact composition, aluminum are all more prone to oxidation and creep problems. The improved composition made them less severe, but compare to copper, they are still there. And some of the ways how to address these problems means more expensive terminal designs.
Now these problems affect mainly thinner conductors, the thicker the thing is, more resistant it becomes. So for relatively thin home installations they are way too much problem vs how much cost and weight savings it may offer vs copper, or the fixes for the aluminum problem become relatively expensive (big part of the extra termination cost to fix the aluminum problems does not depend on the size/rating of the connection, so for low current ones becomes pretty expensive). But for higher current, thicker conductors have inherently less problems to start with, plus the amount of material in question becomes so much it starts to make sense to invest into the more complex connection solutions.

And this is reflected in the standards - aluminum is allowed only 16mm^2 and above (AWG6 and thicker)

For normal home 16A circuit installation the 2.5mm^2 of copper is used (4mm^2 was used with Al),
that in the equivalent 4mm^2 Al, was and in older installations still is causing permanent headaches with connection resistance faults.

Only the main feed and distribution lines, generally significantly thicker than the 16mm^2, are still installed and used with aluminum without any problems. But the important differentiator is the conductor size.

If aluminum have more electrical conductivity than cooper, why most ballast wires are made from cooper and why most electrical cables are made from cooper?

@RRK
Good to know, I'll look out for that from now on

@Laurens
That is true I suppose, wiring cost is relatively small

@Medved
I did not consider that those problems would be worse with smaller gauges that does make sense. Interesting how you have a minimum conductor size for aluminum use there.