Anti blue light screen protector for 21" computer monitors (453 x 282 mm) This product filters out 99% of harmful UV & blue light emissions between 300 and 400nm. This screen protector has a crystal clear picture and does not reduce the HD quality of the device. It is a Class 1 Medical Device by the MHRA to improve sleep, minimise eye strain and eye fatigue, reduce headaches and protect your eyes.