It is not about the voltage rating, but how fast the lamps heat up

The 3.5V lamps you used have lower thermal mass (possibly due to thinner filament), so they heat faster than the other lamps in the string

As the lamps heat up their resistance rises, and so does the share of the voltage they take from the series circuit. They heat up more, the resistance rises more, and so on. Suddenly they get a voltage which is not 3.5V but several times higher, before the other lamps warmed up at all

It will likely be ok if you use identical new lamps for all of the lamps in the string at once, as long as there is no variation between the individual lamps that will cause the same effect or non-uniform filament inside the lamps themselves

@Maxim, sorry to sound greedy or anything like that, but do you have any low wattage HPS fixtures? Preferably less than 100W watts.

I have found myself in a confusing situation regarding old (pre-1997) 35-bulb mini light sets. I recently took home a 35-bulb set of a friend’s (probably from the 1980s or early 1990s) to replace some burnt out and faded bulbs on it. This morning I started to replace some bulbs on it. I tried using modern 3.5V 0.42W bulbs to replace the originals. I quickly found out that this is not the right type of bulb, as they run extremely bright in the set. I tried 2.5V 0.425W bulbs instead (I know some older sets advertised being compatible with “2.5-3.5V” bulbs) and they seemed to work better, but run a bit dim. I ran into a similar situation with a set of my own as well (from 1996). In this instance, the 3.5V 0.42W bulbs blow out immediately when inserted, and the 2.5V 0.425W ones seem to work fine. 3.5V is technically the right voltage for a 35-light set, and all of my modern thick-wire (post-1996) sets work fine with the 3.5V 0.42W bulbs. I am almost wondering if the 3.5V bulbs used in the old sets are of a higher or lower wattage than the modern ones. There is an energy-saving 2.5V bulb (0.25W) that is commonly used on sets longer than 150 lights, but I have never heard of anything similar for 3.5V. Maybe it’s just so old that it’s lost to time? Or is it possible that the 2.5V bulbs are really the right type for these older 35-bulb sets? Even if they aren’t, is it safe to use them in these sets or will they cause the other bulbs to run at a higher voltage?

I've only seen 90W and 120W.

Might have to buy myself one, would you happen to have a list of wattages of the ATBMs used?

I'm back home for Christmas break as I type this.

The ATBMs in Phoenix are awesome. Nice color (3,000K), very good light spread, and not too much glare as long as you don't look directly at one lol. The ATBSs on the side streets are actually 2,700K. I'm extremely impressed with their reliability, too. They've been installed since 2019, and I can only count a handful of failures, which is impressive considering that they have to endure 100°+ summers and haboobs.

What's a swimming schedule?

Very interesting, I'm assuming you're in Phoenix?

I know Tuscan has a swimming schedule on their ATBMs.

Speaking of, I'm assuming you'll be around thousands of ATBMs, how are they?

Geez, it's pretty late in Az isn't it!

The RoadFocus Pluses are a bit glary from the side, but not so much from the underside. Light output and light spread is pretty much average with most other similar LED luminaires.

The Archeon Contemporaries are pretty much same as the RoadFocus Plus in terms of glare, but light spread is a little better.

The Condors are extremely glary, but that's pretty much a given considering that it's a high-mast luminaire with COB optics. The ones that I've seen only have four diodes, so I don't think they provide enough light. Light spread is very good, however.

The WallConnects are a bit less glary than the outgoing Wallpack IV, which is nice. Light output and light spread are about the same.

I've seen some 3 pannel RoadFocus Pluses on streetview. How do all of the LED luminaires that you mentioned perform (glare, light output, light spread etc...)

As far as HID luminaires are concerned, no. I have seen quite a few interesting LED fixtures, though. ADOT is now using the Lumec RoadFocus Plus, Streetworks Archeon Contemporary, and CHM Lighting Condor as well as the new Holophane WallConnect™.