Why is T8 more efficient than T12

[gar]

171223-1414 EST

Theoretically why is a T8 more efficient than a T12.

Most discussions do not go to the fundamentals. If you do some sifting of the information at
http://www.lrc.rpi.edu/programs/NLPIP/lightinganswers/pdf/view/LAT8.pdf
you can get at some of the basics. But it is still not real clear how much is a result of the diameter change vs other changes.

.

 

[junkhound]

My take is that the lower diameter is mostly to limit current for lower wattage. Output in lumens similar to T121 due to improved phosphors.

Back when I started out (52 years ago!) I read the entire IES lighting handbook as one of my first jobs was aircraft emergency escape lights.
There were 3 or 4 pages devoted to why T12 was the most efficient fluorescent with the then available phosphors, had to do with UV and all that,

I should get a current copy from company library and read up on T8. Probably a lot of tech explanations there.