E-readers with a blue light filter are more comfortable for your eyes. The color of the light changes as it gets darker. The e-reader filters blue light, so it emits a warmer light in the evening. This light has less effect on your sleep than an e-reader with backlight, because blue light makes sure you stay focused and alert. This way, you can also read in rooms with low light. With a filter, you can easily read your favorite book in bed, just before you go to sleep.