Hair and rim light

Learning goal

You will be able to adjust light coming from behind the subject so that it separates the hair and shoulders from the background but doesn't spill onto the face. You will explain why hair and skin shine only at a particular angle through the equality of the light's angles of arrival and reflection, that is, the angle of reflection; and you will build a hair light coming from above with a boom arm and a rim light coming from the side and behind, separately. You will adjust the rim width by how far to the side or behind the light is placed, and the brightness of the line by its power, and notice and prevent the cheek spill that appears when the light slides too far to the side. You will compare how straight, wavy, curly and white hair and a bald head respond differently to the same light, and check the trace the rim light leaves on the cheek and the jawline on different skin tones.

The question

The band's bassist liked their frame on the album's inside cover, but wants a separate portrait for themselves: only them, a dark gray background, and a light glowing around their tightly curled hair. In the earlier shoot, when the back light's power went too high, that light turned into a bright white crown around their head and spilled from their ear down to their cheek. This time you try moving the back light slowly. When you put the light right behind their head, a thin, warm line appears at the edge of their hair; when you slide it a little to the side, the line thickens and comes down onto their cheek; when you raise it a little, every curl on top of their hair shines like a small point of light.

Why is the hair shining? Why does the same light become a thin ring once and a brightness spilling onto the face another time when it moves just a few centimeters?

Context

In the multi-light pattern you got to know the back light's job: pulling the subject away from the surface behind it. The back light is perhaps the least forgiving light in the studio: a shift of a few centimeters, a difference of one stop in power, can turn an elegant line into a bright patch spreading over the face. On top of that, the hair's texture and color greatly change how the light will respond to it.

This lesson takes up the back light in two separate forms: the hair light coming down from above onto the top of the hair, and the rim light drawing around the subject from the side and behind. The two do the same job in different places; the adjustment of both depends on understanding at what angle the light hits the hair and the skin.

Simple explanation

Why does hair shine only at one angle?

A shiny surface reflects light like a mirror: at whatever angle light arrives at the surface, it returns at that angle but in the opposite direction. The angle of reflection is the angle at which the light's arrival at the surface and its return to the lens satisfy this equality; a bright patch appears on the surface only when this condition is met. That is why the shine on an oily forehead, a polished table, a wet road or a strand of hair appears only in a particular arrangement of light, surface and camera.

Strands of hair are millions of small, shiny cylinders. When light comes to the hair from behind and grazing it, some of the strands on the edge facing the camera catch the angle of reflection and send light straight to the lens; a bright line or a halo appears at the edge of the hair. When light comes from the front, this angle most often isn't met, because the reflection goes away from the camera; the hair looks matte and flat in the same light. This is why light coming from behind makes hair shine so much.

How are hair light and rim light told apart?

A hair light is light that comes down from above and a little behind the subject onto the top of the hair, lighting the top of the head and the upper edge of the shoulders. It is usually built with a boom arm. A boom arm is a horizontal arm attached to a light stand that extends the light above the subject's head; while the light's stand stays out of the frame, the light itself comes right above the head. A hair light prevents especially the head of a dark-haired person from merging with a dark background, and shows the hair's texture.

A rim light, on the other hand, as you met in earlier lessons, is light coming from behind and the side that produces the bright line appearing on the subject's edge and separating it from the background. It is usually placed on one or both sides of the subject, a little behind, and at head height or a little above. Rim width is how wide this bright line is, and it depends largely on the light's angle. As the light comes closer to directly behind the subject, the line thins and stays only on the outermost edge of the hair and shoulder; as the light slides toward the side, the line thickens and moves toward the face.

Cheek spill is the brightness that spreads onto the edge of the face, the cheek, the ear and the jawline when the rim light slides too far to the side. A little spill can make the face's shape stand out; too much, on the other hand, overlaps with the key light, blows out the edge of the face and makes it obvious that there are two separate light sources on the face. Moving the light a little further back, turning its power down, or putting a flag in front of it controls the spill.

What do power, source and hair texture change?

The back light's power decides the line's brightness. The rim light is most often set at the key light's level, even a little above it; but how much power is needed depends on how much light the hair and clothing reflect. Too much power turns the ring into a bright white crown and the hair's texture is lost. Watching the overexposure warning in the test frame shows the areas that spill and blow out.

The size of the source decides the line's character. A small flash with a grid attached in front draws a thin, sharp, narrow line, and also prevents light from spilling onto the lens or the background. A long, narrow strip box, on the other hand, gives a wider, softer edge stretching from top to bottom.

Hair texture responds differently to light. Straight, shiny hair reflects light almost like a mirror and forms a continuous, bright strip at its edge; even very little power can be enough. In wavy hair the shine gathers on the crests of the waves. Tightly curled hair, on the other hand, scatters light in every direction; instead of a single bright strip, a small point of light forms on every curl, and a soft halo appears around the head. This hair texture often asks for extra power or requires enlarging the source, because the part of the light returning to the lens is smaller. White or gray hair reflects light easily and blows out quickly; you need to turn the power down. On a bald head, a bright patch can form on the scalp; moving the light a little further back or using a soft source softens it.

The rim light also leaves a trace on skin. On dark skin, rim light spilling onto the cheek or jawline forms a bright line depending on the angle of reflection; this line can make the face's shape stand out elegantly or look like an oily shine. Moving the light a little back or turning its power down thins it. On light skin, on the other hand, spilling light easily blows the ear and the edge of the cheek out to white; besides, light passing from behind through thin tissues like the ear and the wing of the nose can make these areas glow a reddish color. In both cases you need to check the edge of the face and the hair's texture up close.

Visual evidence

In the studio you seat the bassist one and a half meters in front of the gray background. The key light is a softbox in front, on the left; behind, on the right side, a small flash with a grid attached in front. While the light is near right behind their head, there is a thin, warm ring on the right edge of their curly hair; every curl shines like a small point of light, and their dark hair and dark jacket break away from the gray paper. When you slide the light half a step to the side, the line thickens and comes down onto their right cheek; on their dark skin a bright strip appears along the jawline. You take the light back and leave the line only on the hair and the edge of their shoulder.

Then, with a boom arm, you extend a second gridded flash above their head, a little behind. The curls on top of their hair light up slightly, and the upper line of the head separates from the background. You turn the hair light's power down by one stop; the top no longer shines, it only shows its texture. The two back lights together separate the bassist's head and shoulder from the dark background with a soft, thin line, while the face stays in the shape of the key light.

Common mistakes

Summary

Hair and skin shine at the angle of reflection, where the angles of the light's arrival and return are equal; when light comes from behind and grazing, the strands at the edge of the hair send light to the lens and the hair is ringed with a bright halo. The hair light comes down from above onto the top of the hair with a boom arm, the rim light draws around the subject from the side and behind; as the light comes closer to behind, the rim width thins, and as it slides to the side, it thickens and leads to cheek spill. The power decides the line's brightness and the size of the source its character; straight, curly and white hair and a bald head need different settings, and the spilling light is checked up close as a line on the jawline on dark skin and a blown-out edge on light skin.

Mini assignment

In this assignment you will move the back light in steps of a few centimeters and follow the result frame by frame.

1. Seat a person in front of a dark background; shoot four frames sliding the back light in four steps, starting from right behind their head and moving toward the side, and note how the rim width changes.
2. Find the frame where cheek spill starts, then prevent the spill by taking the light back a little or putting a piece of card in front of it.
3. Build a hair light from above the head with a source tied to a light stand or a long pole, and try its power at three different levels.
4. If possible, shoot two people with different hair textures with the same back light and compare how the shine looks on each.

Check yourself

• Can you explain with the angle of reflection why hair looks matte in light from the front and shiny in light from behind?
• Were you able to adjust the rim width on purpose with the light's angle?
• Did you enlarge on the screen the trace the spilling rim light leaves on the cheek and jawline, and look at how it changes with skin color?

Glossary

Mini quiz

1. Why does hair look brighter in light from behind than in light from the front?

• A) In light grazing from behind, some of the strands catch the angle of reflection and send light to the lens
• B) Light from behind is a warmer color
• C) The back light is always stronger
• D) Hair swallows light from the front

2. When you slide the rim light from directly behind the subject toward the side, how does the edge line change?

• A) It thins
• B) Its color changes
• C) It thickens and moves toward the face
• D) It doesn't change

3. What is the way to prevent the back light from forming a bright white crown around the head of a white-haired person?

• A) Move the light even further to the side
• B) Open the aperture
• C) Use a larger source and raise the power
• D) Turn the back light's power down

4. In a portrait of a dark-skinned person, the rim light leaves an oily-looking bright strip along the jawline. Which is the most fitting correction?

• A) Turn off the key light
• B) Move the rim light a little further back or turn its power down
• C) Slide the rim light even further to the side
• D) Light the background

Answers

1. A — Shine is seen only when the light's angles of arrival and return are equal; light grazing from behind meets this condition at the edge of the hair.
2. C — As the light slides to the side, it grazes a larger part of the face; the line thickens and spills onto the cheek.
3. D — White hair reflects light easily; turning the power down brings the texture back.
4. B — Light moved back thins the line, and reduced power lowers the strip's brightness.

Summary card

• Shine appears where the angles of arrival and return are equal; the back light achieves this at the edge of the hair.
• The hair light comes from above with a boom arm, the rim light from the side and behind.
• As the light comes closer to behind the line thins, as it slides to the side it thickens and spills onto the cheek.
• Power and the size of the source decide the line's brightness and character.
• Adjust by hair texture; check spilling light on the cheek and chin on every skin.

Bridge to the next lesson

In the bassist's portrait the back lights separated their hair from the background, but the gray background itself stayed the same gray. The band's guitarist wanted the same background for their own portrait, but this time with a tone as dark as charcoal behind them; the keyboardist, on the other hand, was imagining an almost white, bright background. Without buying new paper, can you do both with the same gray background? How does the color of a backdrop change? The next lesson tells how to change the background's tone by controlling its light separately from the key light.