Light painting and light trails

Learning goal

In a dark scene, while a long exposure is open, you will be able to deliberately use the trail a moving light leaves to draw lines and lettering in the air, and light an object piece by piece with a flashlight. You will explain why a light trail is recorded as a line and why the person holding the light doesn't show in the frame, the invisible painter, through movement and darkness. You will show that the trail's brightness depends on the light's power, its speed, its distance from the camera, the aperture and the ISO, while the shutter speed decides only the ambient light and the time set aside for painting. You will light an object evenly with several painting passes, solve the mirror writing problem that appears when writing facing the camera, and keep safety in mind while shooting traffic trails. While painting a face with a flashlight, you will check how the light's hardness and color are recorded on different skin tones.

The question

The shoot at the bridge stretches into the evening. When it gets dark, your friend from the club, while the camera is in a thirty-second exposure, steps in front of the bridge and draws a circle in the air with a small flashlight they take out of their pocket. On the screen, a bright, flawless ring of light hangs in front of the bridge, the stream and the navy sky. Your friend, who drew the ring, doesn't show at all; it is as if the light turned by itself.

In the next frame your friend writes the first letter of their name with the flashlight. The letter comes out backward on the screen, as if reflected in a mirror. In the last attempt they slowly paint the bridge's stone arch with the flashlight; the arch appears out of the darkness like a patchwork quilt, bright in places and faint in others. How do you write in the air with light? Why doesn't the hand holding the light show, and why does the writing come out backward?

Context

You saw how moving subjects leave a trail or disappear in a long exposure, and in night photography how car headlights turn into light trails on roads. Light painting combines these two ideas: what moves is no longer a subject moving on its own, but a light you hold in your hand and direct deliberately. A flashlight, a phone screen or a small LED stick becomes a brush within a long exposure.

This technique looks playful, and it is; but behind it is a fine balance you know from the flash and ambient light lesson (Lesson 19.4). Two separate lights are recorded in the frame: the continuous light of the sky and the town, and the trail of the flashlight in your hand. A photographer who knows how to manage these two separately can balance both a dark scene and the light drawn into it however they want.

Simple explanation

How does a light trail form, and why is the painter invisible?

In a long exposure, each point of the sensor gathers the light that falls on it during the exposure. When a flashlight's light moves in a dark scene, each point the light passes is lit for a short time and recorded; as the light travels, these points line up side by side and a line forms. Light writing is deliberately turning these lines in the air into letters and shapes. Light painting, on the other hand, is moving the flashlight's light over an object to light it piece by piece.

The invisible painter is the person holding the light not showing in the photo. If the person themselves isn't receiving light, they contribute almost no light to the frame; on top of that, because they keep changing place, their body never stays at any point long enough to register, just like the crowd that disappears in a long exposure. That is why wearing dark clothes, not pointing the flashlight at your own face or body, and not standing in one place for long make the painter invisible. When writing with the flashlight pointed toward the camera the trail shows, but the person still stays in the dark.

What decides the light's brightness?

The brightness of a light trail or a painted area depends on the flashlight's power, its distance from the camera or the object, how fast it is moved, the aperture and the ISO. Moving the flashlight slowly lets the light stay longer at each point and makes the trail brighter and thicker; moving it fast thins and fades the trail. A narrower aperture or a lower ISO fades the trail; the setting in the opposite direction brightens it.

The shutter speed, on the other hand, doesn't change the trail's brightness. The trail is recorded only at the moments the flashlight passes; whether the exposure lasts thirty seconds or two minutes, a line drawn at the same speed stays at the same brightness. The shutter speed decides two things: how bright the continuous ambient light, such as the sky and the town, will be, and how much time you have to paint. This is exactly the distinction from the flash and ambient light lesson: the shutter speed manages the ambient light, the aperture and ISO both, and the flashlight's power and speed only the trail. First you set the shutter speed by the ambient light, then adjust the trail's brightness with the flashlight's speed and the aperture.

How is an object painted evenly?

A painting pass is the flashlight's light passing once over one part of an object. To light an object evenly, each part needs to get the same number of passes at the same speed. Holding the light a little too long at one point leaves a bright spot there, and skipping a point leaves a dark gap there. This was why the bridge's arch looked like a patchwork quilt. Moving the flashlight back and forth with smooth, continuous movements, like a painter's brush, and overlapping the passes a little, gives even lighting.

The angle of the light matters too. Holding the flashlight's light from beside the camera, from the front, lights the object flat and without shadows; holding it from the side brings out its texture and shape. Many photographers hold the light while painting not from beside the camera but from beside the object, and so get an object lit from the side, with depth, inside the darkness. A colored gel or a colored flashlight allows painting different parts in different colors.

Why does the writing come out backward?

Mirror writing is writing that someone facing the camera writes in the air normally, from their own point of view, appearing backward in the camera. While you face the camera, your right is on the camera's left; a word you write from left to right advances from right to left when seen from the camera, and the letters come out backward, as in a mirror. There are two solutions: turning your back to the camera and writing in the direction the camera sees, or deliberately writing the letters backward while facing the camera. Flipping the photo horizontally in editing also fixes the writing, but it also flips everything in the scene; if there is a sign or a recognizable building in the background, this means changing the scene.

Light trails in traffic form with the same logic, but they need safety. When shooting at a roadside, on a bridge or on an overpass, you need to stand in a solid spot out of the traffic, place the tripod so it doesn't block the walkway, and get permission if needed.

Painting a face with a flashlight means lighting it with a single small, hard source. When the flashlight is held close to the face and from the front, the shadows are hard and the highlights sharp; holding the flashlight from the side and moving it continuously makes a small source behave like a large one and softens the light. Many flashlights' light is a warm or cool color, and this shift stands out most on skin; setting the white balance to the flashlight's light brings back the skin's own tone. Dark skin reflects the same light less, so it may need more passes or slower movement; light skin, on the other hand, can blow out in a few passes. Because the painted person needs to stay still throughout the exposure, leaning against something helps.

Visual evidence

At the bridge you have set the camera to ISO 100, f/8 and thirty seconds; at this setting the navy sky and the bridge's streetlamps look balanced. Your friend puts on a black coat, holds the flashlight toward the camera and slowly draws a circle; the ring comes out bright and thick, and they don't show. This time they write their letter with their back to the camera; the letter is the right way round on the screen.

Then they move on to painting the arch. They hold the flashlight not from beside the camera but from the left side of the arch, and pass over each row of stones twice at an even speed, like a painter. The stones' texture appears in the light coming from the side, and the patchwork quilt disappears. Finally, they lightly paint the face of another friend from the club, who is leaning on the bridge's railing, moving the flashlight continuously from the side. Their dark skin has leaned toward orange in the flashlight's warm light; when you set the white balance to the flashlight's light, their skin returns to its own brown, and a soft transition of light remains on their cheek.

Common mistakes

Summary

In a long exposure a moving light leaves a line, because it lights each point it passes for a short time; light writing turns these lines into letters, and light painting turns them into lighting an object piece by piece, while the painter is invisible because they stay in the dark and keep moving. The trail's brightness depends on the flashlight's power, speed and distance, the aperture and the ISO; the shutter speed decides only the ambient light and the time set aside for painting. An object is lit with painting passes of equal number and equal speed, writing done facing the camera turning into mirror writing is prevented by turning your back or writing backward; safety is kept in mind with traffic trails, and on faces painted with a flashlight the light is held from the side and kept moving, and the white balance is set to the flashlight's light.

Mini assignment

In this assignment you will work in a dark place with a camera on a tripod and a small flashlight or a phone screen.

1. In a thirty-second exposure, draw two circles by moving the flashlight once fast and once slowly; compare the brightness of the trails.
2. Draw the same circle with thirty-second and one-minute exposures; see that the trail doesn't change but the surroundings brighten.
3. Write the first letter of your name first facing the camera and writing normally, then with your back to the camera; compare the two results.
4. Paint a small object or a friend's face by moving the flashlight from the side continuously; set the white balance to the flashlight's light, then zoom into the face and look at the skin's tone.

Check yourself

• Can you explain which settings you need to change to brighten a light trail, and why the shutter speed doesn't help?
• Were you able to paint an object evenly without leaving a patchy look?
• On the face you painted with a flashlight, did you check how the skin's color and the light's hardness were recorded?

Glossary

Mini quiz

1. What can be done to make the trail a flashlight leaves in a long exposure brighter?

• A) Lengthening the shutter speed
• B) Moving the flashlight more slowly
• C) Closing down the aperture
• D) Lowering the ISO

2. Why doesn't the person holding the light show in the frame in a long exposure?

• A) Because the flashlight blinds them
• B) The camera erases people
• C) Because the shutter speed is too short
• D) Because they stay in the dark and don't stay at any point long enough

3. When someone facing the camera writes their name normally in the air, why does the writing come out backward?

• A) Because the person's right falls on the camera's left, the writing looks as in a mirror when seen from the camera
• B) Because the flashlight bends the light
• C) The camera flips the image
• D) Because the aperture is wrong

4. A dark-skinned person's face painted with a flashlight has leaned toward orange and come out with hard shadows. Which is the most fitting fix?

• A) Doubling the exposure time
• B) Holding the flashlight beside the camera and still
• C) Holding the flashlight from the side and moving it continuously, and setting the white balance to the flashlight's light
• D) Setting the ISO to its highest

Answers

1. B — Slow movement lets the light stay longer at each point; the trail gets brighter and thicker.
2. D — Someone who stays in the dark and keeps changing place doesn't contribute enough light to the frame.
3. A — When facing the camera, right and left swap; writing done normally looks like a mirror image in the camera.
4. C — Moving side light softens the small source; white balance neutralizes the flashlight's color.

Summary card

• A moving light leaves a trail; a painter who stays dark and moving is invisible.
• The trail is decided by the flashlight's power, speed and distance, the aperture and the ISO; the shutter speed decides the ambient light.
• Paint the object from the side, with passes of equal number and equal speed.
• Writing facing the camera comes out backward; turn your back or write backward.
• Paint a face with side, moving light, set the white balance to the flashlight, check the skin by enlarging it.

Bridge to the next lesson

In the last frame at the bridge the sky was still a little bright, while under the bridge it was completely dark. The next morning, when you shot the same bridge at sunrise, you ran into the opposite problem: when the sky was correctly exposed, the bridge's arch and the stream dropped to black, and when the arch was correctly exposed, the sky blew out to pure white. The camera couldn't carry all the tones of this scene in a single frame. How do both the sky and the shadows keep their detail? The next lesson tells about the HDR technique, which gets a wide tonal range by combining frames shot at different exposures.