Optimize The Placement of Lighting Fixtures For Even Illumination
The application of Lambertian properties is a component of light distribution applied to lighting design. Included in these properties are the recognized five types of light distribution, commonly referred to as Types I, II, III, IV and V. These distributions may also be referred to batwing, symmetric or asymmetric. Lambertian properties specifically refer to the reflectance of surfaces that interact with the light.
LED fixtures and diffuse luminaires are designed to emit light in a Lambertian distribution to ensures a uniform spread of light in a space, avoiding harsh shadows or uneven illumination. The Lambertian distribution principle is a key concept in lighting design and optics, particularly in scenarios where diffuse reflection or uniform light dispersion is desirable.
What is a Lambertian distribution and why is it called that?
John Henrich Lambert, a Swiss mathematician, astronomer, physicist, and philosopher, published Photometria in 1760 in which he details his research into the measuring of light. Today we call this subject “Photometry.” Lambert created mathematical equations and then used them to measure the optical properties of materials, quantify aspects of vision and calculate illumination benchmarks.
Lambert began with two simple accepted facts: “light travels in a straight line in a uniform medium and the light rays do not intersect.” In his writing of Photometria, Lambert established the following:
- Illuminance varies inversely as the square of the distance from a point source of light.
- Illuminance on a surface varies as the cosine of the incidence angle measured perpendicularly from the surface and light decays exponentially in an absorbing medium. (quoted from Photometria)
In addition, Lambert proposed that a surface that produces illumination (either a source or by reflection) in a way that the concentration of the emitted light (luminous intensity) varies as the cosine of the angles measured from the surface perpendicular. Lambert stated, “In the case of a reflection surface, this form of emission is regardless of the light’s incident direction, such surfaces are “Perfectly Diffused” or “Lambertian.” (quoted from his book Photometria)
Applying Lambertian distribution in lighting design
The Lambertian distribution is a key concept in lighting design and optics, particularly in scenarios where diffuse reflection or uniform light dispersion is desirable.
Many LEDs and diffuse luminaires are designed to emit light in a Lambertian distribution. This ensures a uniform spread of light in a space, avoiding harsh shadows or uneven illumination. Lambertian emission is also a good balance between efficiency and light distribution, ensuring most of the light is directed toward the area of interest rather than wasted.
In architectural lighting, designers evaluate how surfaces (walls, ceilings, etc.) reflect light. A Lambertian surface ensures diffuse, even light distribution, reducing glare and creating a pleasant ambiance. By considering Lambertian behavior, designers can predict how light scatters in a room, optimizing placement of fixtures for even illumination.
Photometric planning using lighting simulation tools like DIALux and AGi32, often model materials or light sources as Lambertian to approximate real-world behavior of diffused light.
Luminaires such as suspended linear fixtures, or recessed linear lights often incorporate frosted or matte covers to scatter light, mimicking Lambertian emission to soften illumination. In lighting design, the Lambertian model is often combined with other lighting principles to achieve both functional and aesthetic goals, balancing uniformity, energy efficiency, and visual comfort.