Blue light stimulates intrinsically photosensitive retinal ganglion cells, which influence sleep. Visually identical white lights can have different spectra and

Blue light stimulates intrinsically photosensitive retinal ganglion cells, which influence sleep. Visually identical white lights can have different spectra and different effect on these cells. Eg. "warm white" made from RGB with the blue channel turned down, eg. as with f.lux, will probably stimulate those cells more than sharply long-pass filtered (eg. with a dichroic filter) broad spectrum light of the same color temperature. These cells are also responsible for light aversion, at least in animal models, eg: https://www.ncbi.nlm.nih.gov/pubmed/23078956 https://www.ncbi.nlm.nih.gov/pubmed/23078956 , so it could theoretically make a difference to eye strain, especially at high brightness levels. However, if you read the e-ink under fluorescent or LED based lighting it's probably going to have a similar peaked spectrum to the LCD screen and there will be no difference if the brightness and color temperature is the same.