human retinal light cells melatonin circadian rhythms

Light-sensing eye cells help set body timing

Some cells in the human eye respond across a range of light levels. They help regulate melatonin and keep the body’s daily rhythms in step, linking the eye’s response to light with more than sight.

Ancient Egyptian writing helped shape later alphabets

Egyptian hieroglyphs influenced Proto-Sinaitic writing, which developed into the Phoenician alphabet. Phoenician led to Greek, while related writing traditions led to Aramaic. Greek later gave rise to Latin and Cyrillic, and writing based on Aramaic developed into forms including Syriac and Arabic.

The eye adapts across a huge range of brightness

100-trillion-fold

By adapting to changing light, the human eye can work across brightness levels spanning roughly 100 trillion times from dim to bright. At any one moment, however, the range it can handle is much smaller.

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human retinal light cells melatonin circadian rhythms

Light-sensing eye cells help set body timing

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