What Is Reflectance? Meaning, Formula, Specular vs. Diffuse, and How It Is Measured

At Musou Black we judge how black a material is by its reflectance, and we measure it every day. In this article we explain what reflectance means, how it is measured, and what to watch for when you compare reflectance figures from different sources.

What is reflectance?

Reflectance is the ratio of the light reflected by a surface to the light that hits it (the incident light). It is usually given as a percentage.

Light that hits an object is split three ways: some is reflected, some is absorbed by the material, and some is transmitted through it. By conservation of energy:

For an opaque material, which lets no light through, transmittance is zero, so measuring reflectance also tells you the absorptance:

All our black materials are opaque, so we evaluate them this way: low reflectance = high absorption = black. For thin films and other materials that transmit light, you also need to measure transmittance to work out absorptance.

For example, Musou Black Fabric KIWAMI reflects about 0.1% of visible light. If 1,000 photons hit it, only about one comes back, and the other 999 are absorbed.

Light, color and black

Light is a type of electromagnetic wave. The part our eyes can see, visible light, covers wavelengths of roughly 380 to 750 nm. Different wavelengths look like different colors: around 400 nm looks violet, 450 nm blue, 550 nm green, 580 nm yellow, 600 nm orange and 700 nm red.

So what is black? Black is what we see when an object reflects almost none of the visible wavelengths. A perfectly black object would reflect 0% at every wavelength. No real material does that, but the closer a material gets to zero, the blacker it looks.

Types of reflection: specular, diffuse and total

“Total reflection” here means the sum of specular and diffuse reflection. It is not the same as total internal reflection, the effect used in optical fibers.

When we look at things, we mostly see diffuse reflection. A matte black object looks black from every angle because it has very little diffuse reflection. A glossy black object, on the other hand, shows a bright reflection of the light when you look from the specular direction.

Reflectance changes with wavelength (spectral reflectance)

Reflectance is often given as a single number, but in reality it is different at each wavelength. Reflectance plotted against wavelength is called spectral reflectance. An object's color comes from the shape of this curve: a red object reflects red wavelengths (600 to 700 nm) and absorbs the rest, a white object reflects all of them, and a black object reflects none of them well.

The chart below shows the spectral reflectance of our black materials across the visible range.

Even materials with the same average reflectance can look different, and suit different uses, depending on the shape of their curves. And “black at every wavelength” only applies to the light we can see: a material that looks black can still reflect invisible near-infrared light strongly. Black anodizing, for example, reflects about 5% of visible light but over 60% at 850 nm. See Which Materials Reflect Infrared? for details.

How reflectance is measured (integrating sphere)

Specular reflection returns in one direction, but diffuse reflection scatters everywhere. To catch all of it, we use an integrating sphere: a hollow sphere coated inside with a highly reflective white material. Light reflected by the sample bounces around inside the sphere until it is evenly spread, and a detector measures it. Comparing that with the reading from a white reference standard of known reflectance gives the sample's reflectance.

The measurement steps

1. Measure with no light to set the detector's zero (dark reading).
2. Measure a white reference standard to set the baseline.
3. Measure the sample while scanning through the wavelengths.
4. Correct for the reflectance of the white standard itself to get reflectance in %.

Scanning the wavelengths with a spectrophotometer gives a spectral reflectance curve like the chart above.

Why an 8° angle of incidence?

The angle of incidence is how far the light is tilted from the line perpendicular to the sample. If the light came straight down (0°), the specular reflection would go straight back out of the opening it came in through. Tilting it slightly, usually to 8°, keeps the specular reflection inside the sphere, so the total reflectance can be measured.

SCI and SCE on colorimeters

Colorimeters and spectrophotometers used for color measurement often offer two modes:

The glossier the sample, the bigger the gap between SCI and SCE. When comparing data, make sure both values were measured the same way.

We measure total reflectance with an integrating sphere and evaluate blackness as “100% − total reflectance = absorptance”. Our instruments include a JASCO V-780 UV-Vis-NIR spectrophotometer; see Spectrophotometer V-780: Measuring Ultra-Low Reflectance.

What to check when you compare reflectance data

Reflectance figures in catalogs and on websites can change a lot depending on how they were measured. Check these points before comparing:

1. Is it specular reflectance only? This is the most important one. Many sources quote specular reflectance alone as “reflectance”. Because it leaves out diffuse reflection, the number looks small and the material looks very black on paper. We believe how black something actually looks should be judged by total reflectance, including diffuse reflection.

2. What angle of incidence? Reflectance changes with the angle of the light. Most materials reflect more as the light hits them at a shallower angle, so a value measured at 8° can't be compared directly with one measured at 45° or 60°.

3. Which wavelength? “0.5% reflectance” means something different if it is the value at a single wavelength or the average over the visible range. Some materials vary several-fold across wavelengths, so compare at the wavelengths you will actually use.

4. How was it averaged? A “visible average” can be the average over 400 to 700 nm, over 380 to 780 nm, or a value weighted by the sensitivity of the eye (luminous reflectance). Each gives a different number.

Reflectance of black materials: measured values

How low does reflectance actually go? Here are our materials and, for comparison, black anodizing, all measured under the same conditions.

Representative total hemispherical reflectance (angle of incidence 8°). Not guaranteed values. Black anodizing is not our product; we obtained a part and measured it under the same conditions for reference.

Ordinary black objects reflect a few percent of light. Our materials reflect a fraction of that, and Musou Black Fabric KIWAMI, our blackest, reflects less than one fiftieth.

Why 0% reflectance is impossible

In physics, an ideal object that absorbs all incoming light is called a black body. It is a theoretical model; no real material reaches it, for several reasons:

• Fresnel reflection: wherever the refractive index changes, at the boundary between air and a material, part of the light is always reflected.
• Surface roughness: tiny irregularities on the surface scatter light.
• Internal scattering: pigments, fibers and other structures inside the material scatter light, and some of it finds its way back out.
• The material's optical properties: its refractive index and absorption coefficient set a limit on how completely it can absorb light.

Materials made of densely packed carbon nanotubes reach below 0.1% in the visible range, but they are expensive, fragile and hard to work with. Our aim is a black that is practical to use: Musou Black Fabric KIWAMI (about 0.1%) and Musou Black Paint (about 0.6% airbrushed, about 1.1% brushed).

Where low reflectance matters

• Photography and film: backdrops and camera interiors, to cut flare and stray reflections.
• Optical instruments and R&D: telescopes, microscopes, lasers, spectrometers and LiDAR, where even a little stray light affects accuracy.
• Exhibitions and museums: display backgrounds that suppress reflections from the lighting.
• Infrared sensing: materials such as IR Flock Sheet that stay black into the near-infrared.

We can also measure the reflectance of your own samples (depending on the request). If you have a reflection problem, tell us the reflectance and size you need, and we'll suggest the right material.

FAQ

Q. What does reflectance mean?
A. Reflectance is the fraction of the light striking a surface that is reflected back, usually given as a percentage: reflectance (%) = reflected light / incident light × 100. A white reference standard reflects almost 100%; very black materials reflect less than 1%.

Q. How are reflectance and absorptance related?
A. For a material that does not transmit light, absorptance = 100% − reflectance. For example, a reflectance of 0.7% means an absorptance of 99.3%. For materials that transmit light, you also need to subtract the transmittance.

Q. Is there a material with 0% reflectance?
A. No. Every real material reflects at least a little light. Our blackest fabric, Musou Black Fabric KIWAMI, reflects about 0.1% of visible light on average.

Q. Should I compare specular reflectance or total reflectance?
A. To compare how black materials are, use total reflectance (specular plus diffuse). A specular-only figure leaves out diffuse reflection, so it makes a material look blacker than it really is.

Q. What is the reflectance of a typical black object?
A. It depends on the material, but ordinary black objects reflect a few percent. Black matte anodizing, common in optical equipment, measured about 5.7% averaged over the visible range in our tests. Black anti-reflection materials can go below 1%.

Q. Does reflectance depend on color?
A. Yes. An object's color is determined by how its reflectance changes with wavelength (its spectral reflectance). White objects reflect all visible wavelengths well, and black objects reflect none of them well. But invisible near-infrared light can still be strongly reflected by objects that look black.

First published on July 24, 2026. Revised in October 2026.