I still want to get a SOX streetlight (Palomar by Spaulding) but due to the lack of ability of lamps, I unfortunately would have a hard time getting a SOX lamp that cost less than my fixture.
As such I plan on replacing the magnetic SOX ballast with an electronic programmed start fluorescent ballast, and the BY22D lampholder with a 2G11 one, and instead of using a SOX lamp, I would use a PL-L lamp.
Does anybody know what size of PL-L lamp would be appropriate for a 90w SOX streetlight and how I should go about doing this?

A 55W or a 40W PL-L lamp would be a pretty good fit for a SOX 90 sixed fixture. As far as converting it, it's fairly simple. Just find some screw holes in the fixture that match the holes in the ballast (or make your own), the same goes for the lamp holder. Fit them in and connect them. Be mindful that some ballasts can't have long wires running to the lamp, but it should say on them if that is the case. You will still need a lamp support for the PL lamp, the SOX one may work if the lamp rests down on it, or you may need to fabricate a new one. Here is one I did, converting a 35W SOX lantern to 24W PL-L. It's not the neatest job ever, but it looks decent.

It is good to know that you can also run the 36W, 24W, and 18W PL-L CFL lamps using magnetic preheat ballasts.


Here is what to do in a North American electrical system if you want to run PL-L lamps on magnetic preheat circuits:

For the 36W PL-L lamps, you can use a single lamp F40T12 preheat fluorescent tube HX autotransformer ballast in conjunction with a FS4 starter.

For the 24W PL-L lamps, you can use a 2 pin 26W PL-C HX autotransformer preheat CFL ballast in conjunction with a FS4 starter.

For the 18W PL-L lamps, you can use a F20T12 preheat fluorescent tube series choke ballast in conjunction with a FS2 starter.