So right now I've got a 35W SOX lamp hooked up to a Fulham Workhorse WH2-120-C with both red wires tied.
It works well and this has been confirmed by others.

Now I want to run an 18W lamp instead cause the 35 is too bright. For some reason I'm reading that others have used the exact same WH2 ballast with both wires tied for 18W as well. Can someone explain to me if this is actually OK and not over driving the lamp? Wouldn't it make more sense to use one red wire for the 18W (technically 17.5W, but whatever)?

You can find the relevant posts about this here: https://www.lighting-gallery.net/gallery/displayimage.php?album=2302&pos=22&pid=62729

Thanks.

Both are 0.36A lamps, so need a 0.35A current feed. The 18W has just the half arc voltage vs the 36W model.

So when the ballast delivers the 0.35A (or something very close to that) for both arc voltages, it will operate both of these lamps pretty well.
Because the 0.35A is about the matching current for many fluorescents which also vary with their arc voltages across all those types, it is no wonder someone (e.g. Fulham) designed a ballast operating just that way, so inherently able to feed the SOX as well.

Hey Medved, why is it I see different specifications for lamp current? It seems to vary between datasheets. For example:

https://www.assets.lighting.philips.com/is/content/PhilipsLighting/comf1458-pss-en_ca

In that datasheet it puts 18w sox at 0.33A and 36w sox at 0.53A. I'm trying to understand what's going on?

Strange, I just quick-search a SOX36 and there I read 0.35A.
Definitely the current is what matters.
I'm NOT familiar the ballast type what you are using. Some have multiply lamp output channels connected in parallel to the single common inverter stage.
There you may connect these channels parallel, so you get sum of the currents.


[edit:] There was a big error in my text, the "not" somehow disappeared (now in capitals), completely turning the meaning upside down, I'm sorry for confusion before this correction...

Both are 0.36A lamps, so need a 0.35A current feed. The 18W has just the half arc voltage vs the 36W model.

So when the ballast delivers the 0.35A (or something very close to that) for both arc voltages, it will operate both of these lamps pretty well.
Because the 0.35A is about the matching current for many fluorescents which also vary with their arc voltages across all those types, it is no wonder someone (e.g. Fulham) designed a ballast operating just that way, so inherently able to feed the SOX as well.

Thanks for the info. So it looks like they would both work fine.

Side question: Is it normal for a new low pressure sodium to have black ends near the electrodes?
I ordered two of them new and one of them is very black at the base. When I turned it on, it's basically completely opaque. The other one was just slightly black and the blackness went away after I ran it for a few hours.

Did I get ripped off and was sent old bulbs?

There are many types of fluorescent ballasts that can ignite SOX lamps, but do they operate them within specs of that particular lamp? Yes and no.

https://www.lighting-gallery.net/gallery/displayimage.php?pos=-143774
https://www.lighting-gallery.net/gallery/displayimage.php?pos=-116715

It appears that operating them just a few percent over specification will not harm them although I suspect their life gets shortened. You can however operate them by 30% less current and the lamps appear normal  but definitely have less output, and may last as long as their rated life. This is where the WH2 comes in when hooked up to an 18w Sox or Sox-E. I would not attempt a WH2 on a 35w SOX, it's woefully inadequate.

These are the required currents for these lamps:
The 18W SOx is @ 0.35A
The SOX 35W & 55w lamps @ 0.6A.
The SOX 90W, 135W & 180W are @ 0.9A

Sox-E are different. Direct from the Philips catalog:
SOX-E 18, 0.36A @ 52 lamp volts
SOX-E 26, 0.45A @ 72 lamp volts
SOX-E 36, 0.36A @ 114 lamp volts
SOX-E 66, 0.63A @ 110 lamp volts
SOX-E 91, 0.63A @ 166 lamp volts
And SOX-E 131, 0.62A @ 238 lamp volts

Black ends are normal for LPS lamps. They disappear after many hours of operation.

Thanks for the info. So it looks like they would both work fine.

Side question: Is it normal for a new low pressure sodium to have black ends near the electrodes?
I ordered two of them new and one of them is very black at the base. When I turned it on, it's basically completely opaque. The other one was just slightly black and the blackness went away after I ran it for a few hours.

Did I get ripped off and was sent old bulbs?

As far as I have noticed around here, normally they end up black after cathode activation (= one of the latest step in the manufacture process). After burn in (few 10's hours, with burning for few hours uninterrupted for each power on), it should disappear (or get significantly reduced).
An old (used) bulb should have many other signs of long time use: Corrosion around the socket (exposure to humidity), dust heat-stuck on the glass,...

Lightsplus do you think that chart has a mistake on the sox-e 26? Since all the small diameter lamps are listed at 0.36A except that one, and 0.36 x 72v = 26w.

The 26watt SOX-E has virtually the same size as the 35watt, so I couldn't even imagine it being closer to any 18w. It in fact, it's a direct descendant of the 35 watt.

There have been many threads and galleries posted on the 26 watt.
https://www.lighting-gallery.net/gallery/displayimage.php?pos=-190901
https://www.lighting-gallery.net/gallery/displayimage.php?pos=-177925

Thanks lightsplus. So what's the deal with sox-e 36w only being 0.36a then? I thought the e 26w and e 36w should have similar currents like how the regular sox 35 and 55 are both 0.6a?

Two side notes:

I have been running it for probably like 10 hours now and it's still black. The end also occasionally sputters too. Like you know how an old fluorescent light will flicker around the tips when it's wearing out. If I do a hot restrike, then it goes away though. Otherwise it seems new though. No dust or corrosion, so maybe it's just slightly defective.

I put it in my bedroom and there's something I realized. The light emitted by low pressure sodium should likely help before sleep. Research has found that blue/white light keeps you awake. Some people even sell orange glasses for this purpose to wear before bed. I wonder if the low pressure will accomplish this. In addition, we are programmed to associate orange light with nighttime campfires cause that was something we did for a long time in the past.

The SOX-E 36w lamp is the "economy" version of the 55w SOX.

Run your (35W SOX ??) lamp with a WH3, minimum! Or use a WH5 with 2 red wires together (out of 4). This last method still may underdrive the 35w lamp by just a tad.

Yes, there's little blue light; all of the light from SOX is in the photopic visual zone.