What makes sunlight so special?

In our previous article, we explored the key properties of light that are essential for us as photographers. Now it’s time for the more exciting part — let’s put all this knowledge together and apply it in practice.

Our main goal is not only to understand light but also to learn to recreate all possible natural-looking lighting scenarios in our photo studio. As a first step, we will start by analyzing the origin of all the light we observe in nature: the sun. Of course, what we often deal with isn’t necessarily direct sunlight—it can be diffused by clouds or reflected by various surfaces before it reaches our subject. These are all topics for later. For now, we are going to start where it all begins, with the main source itself: direct sunlight.

The sun is a massive object, but because it’s so far from Earth, it acts more like a small light source relative to the subjects we photograph. This causes high-contrast shadows with sharp edges and specular highlights. This is a common way photographers explain and replicate sunlight. But let’s dive a little deeper. If we explore its properties further, we’ll discover a crucial effect of this immense distance: it causes the sun’s rays to travel in nearly parallel lines by the time they reach us. This makes sunlight a very “collimated” light source.

“Collimation” is a term more common in physics than in photography. It describes the process of making the individual rays of a light source more parallel to each other. In photography, you’ll more often hear the term “focusing.” While these two terms are often used to describe the same property in photography, “focusing” has a very different meaning in physics. We’ve discussed these nuances in our article about collimating and focusing light. There, we explain our reasons for choosing to differentiate between these two terms and to use each in its original, physical meaning.

There are three clear signs of a collimated light source that you can easily observe for yourself:

1. Sharp, Consistent Shadows 
   If you hold your hand in the direct sun, the shadow it casts will have hard edges and stay nearly the same size as your hand. Try moving your hand closer to and farther away from a wall; you’ll notice the shadow’s size doesn’t change much.
   
   A quick note: For the sake of this demonstration, I’m simplifying things slightly. Strictly speaking, sunlight is not perfectly collimated. The sun has an angular size of about 0.5°, and this small but measurable divergence is what creates penumbras—the soft edges of shadows.
   
   Comparison: Photographers often see a small light source as a perfect way to simulate the sun. However, a point source creates the opposite effect—the shadows become significantly larger and softer as the subject moves away from the surface the shadow is cast upon. This is one of the reasons you can’t precisely simulate sunlight with just a small light; you start losing important nuances.
2. Parallel shadows
   On a sunny day, look at the shadows cast by different objects like trees, buildings, and people. You’ll see that they all point in the same direction, running parallel to each other.
   
   Comparison: This is another detail that can’t be replicated by using just a small light source in the studio. A divergent light source causes all shadows to fall at different angles, radiating from the light’s position. You can test this yourself by lighting a cup with your smartphone’s flashlight. Notice how the shadow’s angle changes as you move the phone.
3. Consistent intensity
   There is no noticeable light falloff with sunlight. An object 10 meters farther away from you is lit with the same intensity by the sun as an object right beside you.
   
   Comparison: You’ve probably already heard of the Inverse Square Law. It describes how light from a point source gets much weaker as you move farther away; doubling the distance makes the light only a quarter as bright. An important detail that isn’t always mentioned is that this law applies specifically to point light sources, where light radiates outward in all directions. It does not account for collimated light sources like the sun.

Many photographers consider a small point light source to be the best tool for simulating sunlight. While this might be sufficient in some cases, it can lead to unconvincing and unnatural results in more demanding scenarios. By not following the physical properties of sunlight, you lose the small nuances that are a decisive factor in making artificial lighting believable. I also believe every photographer can benefit from being aware of the limitations that different methods introduce.

In this series, our goal is to achieve the desired result in all its richness by paying attention to the small details that set the original apart from its artificial counterparts. For now, it’s enough to remember that to convincingly replicate sunlight, we need an artificial light that fulfils all three of these characteristics.

So far, we’ve discussed the directional properties of sunlight. Now, let’s discuss another key property: color temperature. The color of sunlight changes throughout the day and with the weather. Around midday, sunlight has a neutral-white color temperature of around 5500–6000 K (Kelvin). However, many photographers love shooting during the “golden hours”—early morning and late evening—when the color temperature is much warmer, dropping to around 2000–4500 K. In comparison, most flashes output light around a 5500 K to 5600 K color temperature. This means we often need to consciously alter their color temperature to match the look we want. We’ll explore techniques for this in upcoming articles.

In upcoming articles, we’ll explore techniques for adjusting the color temperature of our artificial lights.

Without discussing any specific light modifiers yet, we can already draw some important conclusions. To simulate the direct sun, an ideal artificial light source must:

• Produce a highly directional, collimated beam of light.
• Illuminate a very wide area. This is a key challenge: a typical small, collimated light source creates only a narrow beam, while the sun illuminates entire landscapes with its collimated light.
• Have an adjustable color temperature to mimic different times of day.

Achieving all of these is not an easy task, but understanding these principles is a valuable first step.

It’s also worth noting that these principles apply when recreating moonlight. Moonlight is just reflected sunlight, so the only differences are its much lower intensity and cooler color temperature.

In our future articles, we’ll explore different light modifiers and find the best tools for simulating the diverse lighting conditions we see in nature.