Every light source produces a spectrum - even a laser, albeit only small one. Have a look at this link: http://www.soundandvision.com/content/led-vs-cfl-bulbs-

Every light source produces a spectrum - even a laser, albeit only small one. Have a look at this link: http://www.soundandvision.com/content/led-vs-cfl-bulbs-color-temp-light-spectrum-and-more http://www.soundandvision.com/content/led-vs-cfl-bulbs-color... As you can see a lot of LEDs have quite a lot of blue. Which is exactly what is responsible for synchronizing your own "clock": http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2831986/ http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2831986/ > Not only does light reset the human circadian rhythm, but the same blue > light that has the strongest impact on dinoflagellates has equal power > to reset our own clocks — although most visible wavelengths can reset > the clock, the blues do the job with the greatest efficiency. Which is the whole reason f.lux became so popular.