What is transmission in light?

Transmission in optics refers to the process where light waves travel through a material or medium without being completely absorbed or reflected back. When light encounters a boundary between two different materials—such as moving from air into glass—three things typically happen: some light is reflected off the surface, some is absorbed by the material and converted to heat, and the remainder passes right through. This passing-through is transmission.

In the context of optical components, controlling transmission is often the primary goal. For instance, optical bandpass filters are engineered to have high transmission for very specific wavelengths (allowing them to pass through) while blocking out the rest of the spectrum via reflection or absorption.

A closely related concept is transmittance, which is the exact, measurable ratio of the light energy that successfully passes through the material to the initial light energy that hits it (the incident light). It is usually expressed as a percentage or a decimal. If a specific optical component has a transmittance of 95% at 532nm, it means 95% of the light at that specific wavelength successfully makes it out the other side.

Several key factors influence how much light is transmitted through a medium:

• Material Properties: Different materials inherently absorb or transmit different parts of the electromagnetic spectrum. Standard optical glass transmits visible light beautifully but blocks certain ultraviolet and infrared wavelengths.
• Wavelength of Light: Transmission is highly dependent on wavelength. A component might be perfectly transparent to 1064nm light but completely opaque to 254nm light.
• Surface Reflections: Whenever light crosses a boundary (like entering or exiting a lens), a portion of it is lost to reflection. This is why anti-reflective coatings are so frequently applied to components to maximize transmission.
• Thickness of the Medium: The thicker the optical component, the more internal material the light must travel through, which increases the likelihood of absorption and decreases overall transmission.