Lesson 4 of 4
Light through the day
Move the sun by hour, season and latitude. See which side of the car is lit, where its shadow falls, and how long it is.
The sun has two coordinates: how high it is and which way it bears. Height decides how long the shadows are and whether the bodywork or the wheel arches get the light. Bearing decides which side of the car is lit and whether you are shooting into it.
Both follow from the hour, the date and your latitude, so all three are controls here. The plan is drawn in the car's own frame with the nose pointing up, which means rotating the car turns the sun around it — exactly what happens when you move the car rather than the camera.
The plan is drawn in the car's own frame with its nose pointing up, so rotating the car turns the sun around it. A face is yellow when the sun reaches it and the camera can see it, blue when the camera can see it but the sun cannot, and grey when it is turned away from the lens.
- The sun is below the horizon at this hour, so there is no direct light and no shadow. Whatever shapes the subject now comes from the sky, from streetlights, or from you.
- Sun height
- -0.7°
- Sun bearing
- 299°
- Shadow length
- no shadow
- Shadow / height
- —
The hour control is local solar time: 12:00 is the moment the sun crosses the meridian, which a clock reports as anything from about 11:45 to 12:15 depending on the date, and an hour later again under daylight saving.
Presets
Why midday is hard
Shadow length is the subject's height divided by the tangent of the sun's elevation. At 30 degrees a car casts a shadow nearly twice its own height, which is a long dark shape you can compose with. At 75 degrees the shadow is barely a quarter of its height and sits underneath the car, and the light arrives closer to vertical than horizontal — so it lands on the roof and the hood, and drops into the wheel arches, the mirrors and the door handles as hard black. That is what the warning under the hour slider is reporting. It is measured, not asserted: the threshold is a shadow shorter than 0.6 times the height of what casts it.
Golden hour, defined
Golden hour is conventionally the period when the sun is between four degrees below the horizon and six degrees above it. How long that lasts is not a constant: near the equator the sun crosses those ten degrees in about forty minutes, and at 55 degrees north in midsummer it takes hours. Drag the latitude slider at a fixed hour and watch the phase chip change without the clock moving.
Which side is lit is your decision
A face is drawn yellow when the sun reaches it and the camera can see it, blue when the camera can see it but the sun cannot, and grey when it is turned away from the lens entirely. The back-lit warning fires when the sun is within 45 degrees of the direction the lens is pointing, which means the surfaces you are photographing are in their own shadow. Sometimes that is what you want. It is never something to discover afterwards.
How accurate this is
The solar position is a low-precision approximation: a sinusoidal declination, fifteen degrees of rotation per hour, and the standard spherical solution for height and bearing. It ignores the equation of time, longitude, refraction and orbital eccentricity, so it takes local solar time rather than clock time and is good to about a degree of height and a few degrees of bearing. That is far more precision than anyone needs standing next to a car, and nowhere near enough for anything that needs a real ephemeris.