The luminance of the sun at noon is 1.6 × 10⁹ cd/m². The luminance of a clear blue sky is around 5000 cd/m² (compared with 300 for a TV display and 150–250 cd/m² for a computer screen). The other sources of natural blue light are the moon and flames.

Currently, there is no evidence that screen use and LEDs in normal use are deleterious¹ to the human retina².