Bihemispherical reflectance refers to the total amount of light reflected by a surface, regardless of the angle of incidence or the direction in which it is reflected. This is an average reflectance value over all possible angles of incidence and reflection.
1. Characteristics of bihemispherical reflection
✅ Measure the total reflection → Not just specular (specular) or diffuse, but all reflection combined .
✅ Direction independent → Uses average reflectance values over an entire hemisphere (half a sphere).
✅ Important for materials analysis → Used in optics, photonics and lighting technology .
✅ Related to the bidirectional reflectance distribution → Often combined with BRDF (Bidirectional Reflectance Distribution Function) measurements.
2. Types of bihemispherical reflection
There are two main types of bihemispherical reflection, depending on how the incoming light is treated:
| Type | Description | Sample application |
|---|---|---|
| Bihemispherical directional reflection | Light strikes at a specific angle, reflection is measured in all directions | Reflectance measurements in architecture (e.g. roof coatings) |
| Bihemispherical reflection (fully integrated) | Light enters from all directions and reflection is measured in all directions | Paint and coating research |
💡 Simply put, Bihemispherical reflectance measures all reflection from a surface, regardless of the angle at which the light strikes or is reflected.
3. How is bihemispherical reflection measured?
To measure bihemispherical reflectance, an integrating sphere is often used.
🔹 Step 1: Light is shone on the surface from a known direction or diffuse source.
🔹 Step 2: An integrating sphere captures all reflected light, regardless of direction.
🔹 Step 3: A sensor measures the total reflection and calculates the average reflection value .
📌 Applications:
✔ Materials research → How reflective is a particular surface?
✔ Lighting & LED optics → How efficiently does a surface reflect light?
✔ Color and Coating Industry → How does perceived color change under different lighting conditions?
4. Difference between bihemispherical reflection and BRDF
| Feature | Bihemispherical reflection | BRDF (Bidirectional Reflectance Distribution Function) |
|---|---|---|
| What is being measured? | Total reflection in all directions | Reflection at specific angles |
| Measuring method | Integrating sphere | Precision sensors for angle measurements |
| Application | General reflectivity of a surface | Detailed lighting simulations and 3D graphics |
| Examples | Paint, coatings, solar panels | Optical simulations, CGI, photorealistic rendering |
💡 In short: BRDF looks angle-specific , while bihemispherical reflection combines all directions into one value .
5. Where is bihemispherical reflection applied?
📍 Architecture & Construction → Reflective roof coatings for energy efficiency.
📍 Automotive industry → Reflectivity of car paints and headlights.
📍 Solar panels → How efficiently do they reflect or absorb light?
📍 Textiles & Fashion → Light reflection of fabrics and fibers.
📍 Medical optics → Reflection properties of medical instruments and implants.
💡 In short:
Bihemispherical reflectance measures all reflection from a surface , regardless of the angle of incidence or direction of reflection. This is used in optics, lighting, architecture, and materials science to determine the average reflectance of a surface.