I tried that, but the sim didn't seem to converge.

I had trouble reproducing your result. What do you mean by V(Vin) ?

 

I had trouble reproducing your result. What do you mean by V(Vin) ?

In LTspice, V(Vin) is the voltage at node labeled Vin.
Similarly V(1) is the voltage at node labeled 1.

 

Correction.
I was wondering why the series simulation values were some different than my previous sim of them separately, and I found an error in the series sim.
I was using the Vin voltage for the 25W bulb equation instead of the node 1 voltage.
The corrected sim below now agrees with my separate simulation, (but unfortunately not as close to OBW0549's measured values).

View attachment 172954

Hi,

Ok i got the same result using your models and using pure math by entering all the constants and letting the node voltage v1 be the parameter. This gave me results:
v1=86.5403411319136

as the voltage across the bottom bulb, and
vd=33.4596588680864

as the differential voltage across the top bulb, and
i=0.1771478276077

as the series current.

The equation to be solved was:
(51.264*v1^0.5054+32.04*(120-v1)^0.5054)*v1-6151.68*v1^0.5054=0


The formulas i found in the EE manual produced a voltage of:
v1=83 volts which is close to 86.5 roughly.

In LTspice, V(Vin) is the voltage at node labeled Vin.

Ok no problem, i usually use lower case 'v' but that's ok.
That makes V(Vin) or v(Vin) equal to 120 volts always for this problem anyway.

 

i usually use lower case 'v' but that's ok

And I see you also use i for I.
Spice, of course, ignores the case of a letter, which has caused much simulation results confusion for newbies who try to use M for megohm.

 

And I see you also use i for I.
Spice, of course, ignores the case of a letter, which has caused much simulation results confusion for newbies who try to use M for megohm.

Hi,

Yes i dont worry about silly things like that just like an apostrophe in words like don't because the context is almost always clear that dont means don't and that is one less character wasted in a phone text message for example.
The reason i questioned the capital "V" was because "V" was used as a variable for a particular voltage. For example:
V=12.5
v2=V(vx)

I figured it was such but just wanted to be clear. The calc's all came out right though.