Good day. As the title of the post suggests, I'm looking for the operating current of the F15T8 lamp. I have a vintage desk lamp I removed from service and realized it had an incorrectly rated ballast in it, but worked fine for at least 5 years. I did a quick test this morning and found that the current on a Kill-A-Watt is .33A. For those that don't know, the current on a series circuit is the same throughout and a line current of .33A in a simple choke ballast circuit means that the lamp current is also .33A.

DieselNut's General Electric 8G3912 specifies 300 mA.
xmaslightguy's Power Lighting 8G3912 specifies 305 mA.
Universal's 1977 ballast catalog specifies 300 mA
On Gallery of Lights, two posters each found different specs: 51 V 340 mA from Philips, 14.5 W 55 V 300 mA from IESNA.
Sylvania Lighting Australasia's Fluorescent Tubes Range book specifies 55 V 310 mA.

So your DUT's 330 mA is A-okay.

Something to like about (General Electric / Valmont / Power Lighting Products)'s ballasts is, they listed on their labels, lamps with their current ratings.  (Some later label revisions are less informative than earlier revisions.)

(Initially posted 2019-10-31.  Revised 2020-04-30 added SLA book.)

DieselNut's General Electric 8G3912 specifies 300 mA.
xmaslightguy's Power Lighting 8G3912 specifies 305 mA.
Universal's 1977 ballast catalog specifies 300 mA
On Gallery of Lights, two posters each found different specs: 51 V 340 mA from Philips, 14.5 W 55 V 300 mA from IESNA.
So your DUT's 330 mA is A-okay.

Something to like about (General Electric / Valmont / Power Lighting Products)'s ballasts is, they listed on their labels, lamps with their current ratings.  (Some later label revisions are less informative than earlier revisions.)

Well it took me long enough to get back to this thread, but thank you. I think I may have wondered about this before and remember somewhat faintly reading that a 100V/50Hz ballast was usable on a 120V/60 Hz line and I guess it was right. Also helpful for the Japanese, as only two types would be needed instead of three. Japan has three electrical standards. Eastern Japan is 100V/50 Hz, Western Japan is 100V/60 Hz and Okinawa is 120V/60Hz.

Osram specifies 330mA / 55V (with 440mA preheat current)...

So seems anything between the 300..330mA should be OK...

On the US Sylvania GTE bulletin, the F15T8 is rated for 57v 300mA operation approximately. All F15T8 tubes in the world are electrically interchangeable with each other on the exact same ballasts from what I can understand.