[Trisquel-users] Re : how do you read your books: pdf or html?

[lcerf]

I do not think it makes any difference: in both cases, the CPU probably runs  
at the lowest available frequency ('cpufreq-info' in a terminal can tell you  
the current frequencies).  The same holds for the GPU (if you have a separate  
video card).  You can reduce the brightness of the screen to save energy.   
And do not believe that a black background wastes less energy than a white  
background: it was the case with CRT screens but it is not true for LCD  
screens (it usually is the opposite!):  
https://www.scientificamerican.com/article/fact-or-fiction-black-is/