The basics of light logic

Light logic is exactly that. It's logically where the light is coming from. You've now got a look at the characteristics of the light. Is it a hard, piercing sunlight or is it a soft, diffused window light? And by looking at these characteristics, you can then start to understand how the shadows work within that scene. So let's look in more detail at how light falls, and to start with, we can just use this sphere and see how the light falls on that. First, we're going to look at the cast shadow that is created. The first thing to think about is light always travels in a straight line. And the shadows that are cast by the light are always in a direct response to whatever that light hits. So if we look at these two spheres, the first example the light is coming from almost directly above it. The cast shadow is very short and sphere-shaped. In the second example, the light is in a much lower position, just like the afternoon sunshine would be much lower in the sky. And because of this, the cast shadow is a lot longer. It's still got elements of that sphere shape in it, but it's just been elongated. So now it's more of an ellipse shape. The characteristics of a cast shadow are dependent on the hardness or the softness of the light source, and also how light or how dark the value is of the object that we're looking at. And when I talk about value or tone, I'm just describing how light or how dark a subject is. So white would be a light value or a light tone, and black would be a dark value or a dark tone. So, hard light would produce a cast shadow with a sharp edge. And a soft light would produce a cast shadow with a more blurry edge. So let's have a look at some basic 3D forms. And I've lit these with a light that has been slightly diffused, so you can both see sharp and soft edges. If we start with a cube, you can instantly see that there is a more angular shape to the shadow. And you notice how the shadow is sharpest nearest the form. And then the edge of the cast shadow becomes softer and softer, as it gets further away from the light source. And this softness is just like this fermato we saw on Mona Lisa's face. It's also darkest directly under the shape, where the least amount of light will be hitting. So let's have a look at this cylinder shape to go through the different things are to observe about the light logic, before I begin to draw the subject. So the first thing to work out is what is that angle of the light? So I'd always look for the brightest area first, the highlight. And on the cylinder, I can see the highlights in the top here of the cylinder. And then I'd look to see how long the cast shadow is, where the cast shadow ends. And this gives a good judge of the location and direction of the light source, if you just take a line between the end of the cast shadow, and the highlight in your image. The second thing is what is the intensity of the light source? And I determine this by looking at how sharp or how soft the edges of the cast shadow. The third thing is how flat the surface is the object is sitting on. And if you've got an uneven surface, it can alter the shape of the cast shadow quite dramatically. If you look here at the creases in the table cloth, it has thrown the shadows into these really angular shapes. So if you were trying to draw a realistic rendering of the figs, you'd make it harder for yourself if the cast shadow has got these angles in because it doesn't logically sit with the shape of the actual figs, the shape of the first form. So if you can try to match the shape of the cast shadows with the shape of the object you're looking at, it'll make it a lot more realistic drawing. So when you're first starting to understand form, it's easiest to split it into three distinct areas. The lights, the darks and the cast shadow. The first is the light side and this includes the highlight in the half tones. The highlight is the very lightest part is where the light directly hits the object. So it's the best indicator when you look at your subject to determine where and what angle the light is coming from. And highlights can make the drawings come to life. The halftone zone within the light side and they're always going to be lighter than any other value on the shadow side. They often blend into the shadow side, but this is the line that you're looking for to split between the light and the darks. And this can have many names, it can be called the bed bug line, the shadow line, the terminator, the form shadow line, just to name a few. The main thing to remember is to keep each area clearly defined. The shadow side is a secondary to look for in the form, and this includes the form shadow, the form shadow core, and reflected light. The form shadow core is the darkest part of the shadow. And the rest of the form shadow is made up of dark tones that blend away from the core shadow and turn into the reflected light. Reflected light is a light reflected onto the subject from the surface it sits on, so it's an ambient light around the object. If the object was sat on black, there wouldn't be any reflected light. But if it's sat on white, then that would be more reflected light bounced back. But reflected light is handled well. It can give your drawings that real or how did you that drawing? It can really give that sense of realism to them. So, it's worth taking your time with the reflected light, but just take it very gently. And then we have the cast shadow, and this has three main parts. The darkest part that sits directly under the object. The, also dark part, but more of a mid-tone that makes up the majority of the shadow shape. And the lightest part or the end of the cast shadow, which is that, the softest tail of the cast shadow. Keeping your light tones in the light side, and your darks in the shadows, while still maintaining this soft transition between the two is what we're trying to achieve. What often happens is that you observe the light logic to start with, and you can see the cast shadow quite obviously. But you don't go dark enough in the cast shadow and also not dark enough in the form shadow. And understanding the form shadow, and going dark enough in this, is key to giving you that sense of realism and three dimensionalism into your drawings.