It's not just psychological. According to some measurements the cold light from screens, neon lights, white LEDs etc. causes an increased heart rate, making it

It's not just psychological. According to some measurements the cold light from screens, neon lights, white LEDs etc. causes an increased heart rate, making it more difficult to fall asleep. The Voyage is supposed to have a warmer backlight mode, but I only have experience with the Paperwhite(I only read during the day anyways).