Product Photography: Measuring Light

• These notes cover the basics of light as it pertains to product photography, including how to measure and transform it.

The Amount of Light

• To accurately adjust a camera, it's essential to determine the quantity of light present.
• Viewing the camera screen or histogram isn't accurate because they show JPEG previews and transformed data, not RAW files.
• A light meter or exposure meter is needed to measure light accurately.
• There are two kinds of measurable light: incident and reflected light.
• Illumination is the amount of light an object receives (incident light).
• Luminance is the amount of light the object returns (reflected light).
• Measuring reflected light doesn't reflect the actual light from the source, but what remains after absorption by the object.
• A pile of coal will reflect less light than snow, even if the same amount of light falls on each.
• A reflection coefficient (reflectance) is needed to determine the true measurement for each object.
• It is preferable to measure incident light using an independent exposure meter/light meter.
• An independent exposure meter allows you to measure the light projected onto an object, its progressiveness, appropriate camera settings, and how much light needs to be added or removed.

The Quality of Light

• Four factors determine the quality of light: apparent size, distance, reflection, and diffusion.
• Apparent size: A larger apparent light source creates softer light, while a smaller source creates harder light.
• Distance: The closer the light source, the softer the light; the farther, the harder. However, increasing distance also reduces the apparent size.
• Reflection: Light reflected by a surface (like a white wall) expands the beam and softens the light.
• Diffusion: Diffused light (e.g., through fabric or clouds) is softer than direct light.
• Observing the penumbra, or half-light at the edge of the shadow, helps deduce the quality of the light.
• Light quality doesn't determine if a shadow is light or dark; shadow luminance depends on the surface it's projected on and the light reflected by the environment.
• Making light softer can be done by bringing it closer to the subject, using a larger shaper, or by using a diffusing fabric between the light and the object.
• Studios can change light quality by adjusting the size and distance of light sources, using softer shapers like light boxes or umbrella lights, or harder ones like zoom bowls.

Contrast

• Contrast needs to be managed to emphasize or hide textures on an object.
• Low-contrast lighting provides slight homogeneity, ideal for smooth-skinned fruit.
• High-contrast lighting creates ruptures and threshold effects, perfect for photographing oranges and pineapples.
• Bringing the light source closer increases contrast.
• Moving the light source away flattens the image.
• The sharpness of the light beam's angle on an object and the proximity of the light source make contrasts more visible.
• Distant light sources result in more evenly lit hollows and peaks.
• The color of light plays an essential role in the color rendering of a photograph
• Our brains automatically balance colors.
• The kelvin scale allows us to quantify the color of a light source.
• Lower Kelvin temperatures mean redder light
• Higher Kelvin temperatures mean bluer light.
• "White" light is calibrated at 5500K, and the "absolute" white is CIE at 6500K.
• Cameras need to know the real color of the object's illumination.
• White balance in photography and videography is actually white compensation for the color that is being emitted.
• To get an image that is faithful to how we perceive the color, the opposite adjustment must be made.
• The camera needs to be adjusted to between 1800K and 2200K to be precise.
• The white balance can be customized, thanks to calibration with a gray card.
• Precise adjustments can be made when photographing a gray card in the same lighting you will be using for the shots of an object.
• To effectively correct the white balance for the photo, follow these steps:
• Place the gray card in the same location and under the same lighting conditions as the object you want to shoot.
• Take a photograph, being careful to correctly expose the photo using a flash meter.
• Use the camera's "custom white balance" and select the gray of the photographed card as basis.

The Roles of Light

• A single light source creates visual evidence and avoids issues with overlapping shadows when following product-lighting conventions.
• The primary source, representing the sun, is referred to as the key light which has to be more powerful than all other lights..
• The secondary source represents the reflection, is opposite the primary light, is weaker and more diffuse, and is referred to as the fill light.
• The light that is placed behind the object is called the backlight.
• The light is positioned exactly opposite of the object, outlining the object's edges in silhouette, is called the rim light.
• A light source that is directed toward the plane behind the object is called the background light.
• The light source can be placed to illuminate the entire scene or give it a particular atmosphere, and this is called ambient light.
• The goal is to make it appear as if there is only one light source by adjusting the intensities and qualities of the lights, and carefully choosing their angles.
• Most product-lighting arrangements require only one active light source.

Distance

• The light source's distance affects quantity, quality, contrast, and role.
• Even if the received light quantity is the same, the result will be completely different given whether the distance is short or far.
• The light will be much softer with high contrast if the distance is close, conversely if the distance is much farther away the light will be harder with reduced contrast.
• Isaac Newton's inverse square law states that light decreases more and more slowly as one moves away from it.

Angle

• The object's visual appearance and shadows change radically based on the light source's placement.
• Shadows narrow as the light source moves overhead, disappearing completely at the nadir, and stretch disproportionately with a lateral light source.
• The shape, size, reflections, shade, and color of an object shifts depending on the angle of the light.