“Flicker is a discomforting artefact of poor lighting and consists of a rapid variation in the intensity of light, which occurs in a cyclical manner.
Some frequency ranges are more noticeable to people than others, and there is a certain frequency above which the eye cannot detect the changes in the light level. This is referred to as the flicker fusion threshold or persistence limit. However, this limit is different for different people and noticeability of flicker relates also to the amount of variation of the limit, known as the flicker index.
How noticeable the flicker will be also depends on the part of your eye that is viewing the light. Seeing the light out of the corner of your eye will give a different flicker perceptibility to the centre of your visual field. If your eye is moving – or adapting to the amount of background light – this will also have an effect.”