Daylight changes constantly without us thinking about it. From the moment the sun’s warm pink rays strike the horizon until it reaches its highest point in the sky and emits a cooler light.
The amount of light received by our eyes has a direct effect on how we feel. When it’s dark, the sleep hormone melatonin is produced. When luminous intensity is at around 300 lux, production of cortisol increases, which reduces melatonin production, and we become more alert. This effect continues up to around 1,000 lux, at which point it plateaus. Therefore, purely hormonally, we are no more alert sitting on a sunny beach than we are on a park bench on a cloudy day.
The colour temperature of the light is another thing that changes throughout the day without us thinking about it. While all people react the same way to luminous intensity, we react differently to colour temperatures – it’s more a matter of preference. However, it is attested that blue light over 4,500 Kelvin has a stimulating effect. The reason for this is believed to be because our brains have evolved under a blue sky for 7 million years.