How do you figure out the length of a cast shadow?

It seems like a simple question. So why did I get totally lost during our Members’ live critique session last Saturday (a monthly webinar for the Master Oil Painting Membership)?

My Lapse in Memory


I learned and practiced perspective terms and concepts over and over during art school. Why did all that knowledge abandon me 30 years later? After all, I’ve been painting from life and using perspective constantly.

As it turns out, that’s exactly why I got lost.

When we paint from life everything is in front of us. We don’t need to know mathematical formulas or remember exact terms and concepts. We just need to see values, colors, edges, lines, and form and arrange them in a beautiful way.

Painting Art Shadow Length

Pure Gold 24×30 – oil painting by Bill Inman

Lucky for all of us, understanding just the basics of how light and shadow, perspective and 3-dimensional shapes work is enough to help us create beautiful and believable paintings.

When we paint from life on a regular basis we get a strong sense of how things work together. That allows us to move things around and compose our paintings while keeping a wonderful feeling of reality.

Is that a good reason to ignore learning about perspective or refreshing my memory?

Nope, it sure isn’t.

Fortunately, I have a great book on perspective that brought it all back (well, maybe not all, but enough). If you have a chance to grab a copy of Basic Perspective for Artists I’d recommend it. It was written in 1995 by Keith West and describes all the concepts the average plein air or realist painter would need.

I should tell you though, it’s not a nail-biter, keep-you-on-the-edge-of-your-seat kind of book. I think my head bobbed from dozing off at least a half-dozen times. Then again, I’m kind of a “ooh, pretty picture” type of reader (which might explain my lapse of perspective concepts memory).

Painting Art Shadow Length

Basic Perspective for Artists – art book by Keith West

After refreshing my memory I learned that the part of the equation I was missing during the webinar mishap was the ‘Shadow Vanishing Point’.

Shadow Vanishing Point

The painting you saw me in the process of critiquing in the earlier video was submitted by Kathy Rivera (, a Master Oil Painting student. Her work is beautifully done, and because of a question asked by another member during the webinar, it offered a very lively discussion about perspective and shadow length.

Painting Art Shadow Length

Winter Barn by Kathy Rivera (Master Oil Painting student)

Kathy was kind enough to let us use her painting to continue our shadow length conversation here.

Let’s start with some basic definitions and descriptions of Vanishing Point elements.

Basic Definitions and Descriptions

Painting Art Shadow Length

Notice the line placed on the thickest part of one of the tree trunks (the bright turquoise vertical line). I did a part of the tree rather than the whole length because the top part is so thin its shadow would generally fade away quickly in real life situations.

I drew a dotted line straight down from the light source. Where it intersects the horizon line is where you’ll find the Shadow Vanishing Point (bright turquoise dot).

The horizon line I placed with dotted lines is approximately where I thought it might be (horizon lines can be a bit subjective since they’re basically where the sky and land meet).

We’ll dive deeper into this in a minute, but to find the length of a shadow you can draw a line from the light source past the top of the object, and then another line from the Vanishing Point past the bottom of the object. Where those two lines intercect is the approximate shadow length, at least most of the time. We’ll talk about an exception to that rule when we get to Low Light sources towards the end of the blog.

How NOT to Calculate Vanishing Point

Painting Art Shadow Length

Since the mistake I made is pretty common among artists, I thought it worthwhile to show ‘what not to do’.

During the critique webinar, I confused myself because I tried to create the shadows by drawing a line at the top and bottom of the tree directly to the light source. This caused the shadow to shoot off in a wonky direction with the wrong length. I knew it wasn’t right, but couldn’t immediately figure out what I had done wrong…

“What was that confounded perspective formula we used in art school again?”

The experience was both embarrassing & awesome!

Embarrassing because I probably confused everyone at the webinar, but awesome because it showed that professional artists don’t typically rely on formulas for their artwork. We don’t need to remember a bunch of formulas or concepts to paint successfully from life.

It also created another excellent teaching opportunity, which is something I’m always excited about.

Why Understanding Vanishing Point Matters

I thought to myself, “If I had been out on location or painting from imagination I would have instinctively made the shadow what I felt was a good length. It would have looked natural. Problem solved.”

But why does that feel so instinctual to me?

It seems so easy to say we can simply move things around and change the size of this or that when we feel like it. In reality, it can become frustratingly complicated and soul-stretching to create a painting that reaches the hearts and inspires the thoughts of others.

When I paint on location I’m often in learning mode. How is the light affecting the colors and shadows when the sky is roiling with storm clouds? What does the edge of a reflected light look like on a grey rock compared to an orange one?

That’s why understanding the nature of perspective and ‘shadow vanishing point’ is not only useful but crucial. I may have forgotten the term during the webinar, but all of my early training was still informing my decisions.  Painting out in the field with a knowledge of perspective caused me to observe nature with greater clarity and nuance.

It’s why when working on a painting with buildings and strong shadows in my studio, or from imagination, I’m able to instinctively compose paintings with believable realism. That was the situation with Breakfast is Ready.

Breakfast is Ready 24×36 – oil painting by Bill Inman

This house was taken from a neighborhood in Hays, Kansas where I completed my MFA, but almost everything else in the painting was from my imagination.

The reason I was able to pluck this home from a city street and believably place it in an imaginative setting was my understanding of perspective.

Calculating Vanishing Point (the right way)

Now that we know how not to calculate vanishing point, and we’ve discussed the importance of understanding the concept, let’s dive into the correct way of figuring out shadow length.

We’ll do that by analyzing 3 different images depicting a High, Mid and Low height for the light source.

High Light Source

Painting Art Shadow Length

When the light source is high like the mid-day sun the shadows tend to be very short. The strongest part of the shadow will be closest to the trunk, and the shadow’s edges will grow progressively softer as it moves away from the tree.

The examples I use show approximate length and direction, but I didn’t illustrate how quickly the shadow would likely fade. Here’s a painting of mine from a few years ago that shows quickly softening shadow edges resulting from a high light source.

The Dance 30x24 by Bill Inman (2003)

The Dance 30×24 by Bill Inman (2003)

That softening of the shadow’s edges occurs no matter how long the shadow. However, the transitions when the shadow is shorter show up much more quickly.

Mid Light Source

Painting Art Shadow Length

As the light source moves lower the shadows naturally grow longer and often travel right out of the painting. Since the viewer will seldom see the light source in the painting they won’t know precisely where it’s at. That is why we can play with the shadows, as long as we keep them consistent.

Longer shadows can be a lot of fun to work with. Notice that as the shadow travels across the road it doesn’t move in a rigid straight line. The shadow glides across the snow bank, slides down the raised edge, travels across the road and then shifts up again as it hits the other bank of snow.

That gives us wonderful opportunities to increase variety and make our paintings more engaging.

Low Light Source

Painting Art Shadow Length

Notice in this last example that the top line moves straight across the painting. That line will never touch the ground. Does that mean the shadow will go on forever?

No, of course not.

Remember earlier when we mentioned that the top branches were so thin that they would fade away quickly? That’s what will happen with our shadow in a lower light source situation. Even though the light waves will travel seemingly without end, the particles of dust and moisture in the air will filter and block those light waves until they eventually lose strength.

That’s part of why the shadows’ edges grow increasingly fuzzy as they move further away from the object.

Concluding Thoughts

The shadow vanishing point works indoors and out, but it’s important to understand that shadows from artificial light behave differently with natural light sources. It’s much more complicated with artificial light because the vanishing point isn’t on a horizon line.

There are also more steps involved when the object is a geometric shape, like a box or cylinder. Maybe I’ll cover more about that in a future post. Let me know in the comments if that’s something you would find useful so I know whether researching and writing that blog would be worthwhile.

And remember, just as with any other art principle, understanding shadow vanishing point will only make you a stronger artist if you don’t allow formulas to rule your painting.

The wonderful thing about art is that we don’t have to make the shadows precisely as long or short as they might be in real life. If the painting’s design will be stronger with shorter shadows, then we use shorter shadows. If longer shadows add greater drama, then do that.

Observe and use what nature teaches you. If we are consistent throughout our paintings, especially with our light source, we can get away with a lot of improvising as artists.

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