As the title suggests, when were the Lifeguard electrodes removed from Philips lamps?

I would say sometime between 1994 and 1998.

I have a Philips bulb from 1992 with large electrodes and one from 1995 with small electrodes.

I am pretty sure it is 1995 then, because I have a Philips 175W MV bulb on my eBay watch list from 1994 with modern Philips packaging and design, yet it still has the huge Lifeguard electrodes.

The “Lifeguard” electrodes were in fact never stopped - only the brand name was phased out.   Lifeguard refers to the type of emitter coating on the electrodes.  That was first introduced from Europe to America by GE in 1958 with its Bonus Line brand, followed by Sylvania’s Banner brand in 1960 and finally Westinghouse’s Lifeguard brand in 1961.

This style of emitter coating was maintained almost without change right up to the present day.  It became so ubiquitous that once all manufacturers had it there was no need for a separate brand name to indicate its presence.  As far as I know, Westinghouse dropped the name in 1989.

In the years following the takeover by Philips, several improvements were made to the dimensions of the Westinghouse electrode coils designs but always maintaining the same basic “Lifeguard” design.  One problem with some of Westinghouse’s electrodes was that they were simply too big.  Aside from wasting costs, they conducted too much heat away and notably lowered lamp efficacy and lumens.  Some also took too long to transfer from the initial glow discharge to the arc, after switching on.  That caused accelerated degradation and lumen depreciation during life.  A long overdue improvement was triggered by the lumen and life race of the 1990s, when all manufacturers became much more competitive and could no longer afford to keep outdated inefficient designs in production.  Customers were beginning to realise that Westinghouse’s mercury lamps were actually pretty poor by comparison to foreign competition and even other USA manufacturers. Their lumen output was worse and they blackened faster.  The electrode improvements introduced by Philips helped raise both the initial as well as through-life performance to much more competitive levels.

This emitter turns the arctube white, so why the arctube turns black then?

@James Ah, I see. But I thought that the bigger electrodes made the bulbs last longer? Isn't that right?

Lasts longer at the expense of lumen efficacy I think.

@dor123 - I think you are right. That's why they are the everlasting bulb, but not necessarily the brightest throughout life...

There is an optimum electrode dimension and geometry for each lamp wattage / current rating.  If the electrode is too small its life will be reduced due to higher temperature operation - but also if it is too big, life will be reduced due to delayed GTA (glow-to-arc) transition time and increased sputtering damage.  Westinghouse's old designs were apparently quite severely oversized and date back to a time when these finer details were not known.  Other manufacturers upgraded their electrodes quite early, but Westinghouse was kind of left behind from about the 1970s onwards.  Some of its lamps may indeed have lasted quite long, but since a lamp typically consumes about a hundred times more cost of electricity than its own initial purchase price, consumers quickly began to realise that it was costing them a lot to buy those inferior old lamps that consumed a lot of power for a rather low light output.

@dor123 the emitter coating indeed has a whitish colour, but tungsten is also lost from the electrodes and that is black.  The net result is that the arc tube appears to become black as it ages.

Would that mean that the big electrodes would only increase life when the bulb is run continuously with zero shutoff? But when run D2D, it would result in lower life, yes?

That’s a good point!  I don’t know for sure, but I suspect your theory is probably correct.

Just two questions, James. I've always noticed how small the auxiliary electrode is in mercury vapor lamps. Would making it bigger, meaning thicker, increase the number of times you could start the lamp, or would it just sputter away and decrease the number of starts you could do? Second, why is the section on electrodes for MV lamps crossed out on your website and not found on the server?