Based on a discussion some weeks ago about the difference between photographing sunrise and sunset, I have been recording the color temperature changes... and learning to enjoy waking up early... today was a unique day in the on going test... there were clear skies at 4:51 AM and 18:20 PM... let's take a look.
To be correct color temperature measurements are in Kelvin and like other aspects of photography the logic is reversed... larger Kelvin values are cool and low Kelvin values are warm...
Color temperatures over 5000 K are blue-white and referred to as "cool colors"
Color temperatures (2700–3000 K) are yellow-white and called "warm colors"
Vertical daylight and electronic flash are considered to be 5500 K
The testing is still in process, but here are the results from today...
In general, during sunrise the color temperature gets progressively warmer while at sunset the color temperature gets progressively cooler... and typically the change is more pronounced at sunset... it's a little counter intuitive as we normally have red & orange sunsets... that quickly turn bluish as the sun dips below the horizon.
Here are the actual measurements from today (29-April-2017)...
The "mired" is a unit of measure along the Blue & Amber axis and indicates how strong a warming or cooling filter needs to be to keep the same or a reference white balance... (1,000,000/Kelvin=Mired). In the case of sunrise we would need a progressively darker blue filter while at sunset a progressively warmer filter would be required. If shooting daylight film the reference is 5500 K or 182 Mired.
CC (Color Correction) is a measurement along the Magenta & Green axis. Sunrise is fairly stable while we see a variation at sunset.
The test is on going... and so far I have managed to struggle to the balcony at 4:45 AM...
Casey