New to Optics?
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A good place to start
What does an optic actually do?
You don't need to know every optical term before you begin. The simplest place to start is with what you're trying to do with the light.
An LED produces light, but that light isn't necessarily going where the application needs it. An optic controls and redirects the light to create a useful distribution — whether that's a narrow beam, a wide beam, a more uniform output or light directed towards a particular target.
The shape of the light
How do we describe a beam?
Once an optic starts controlling the light, we need ways to describe the result. These are some of the most common terms you'll encounter when comparing one beam with another.
Beam angle
A way of describing how narrow or wide the main beam of light is. A smaller angle generally means a narrower beam; a larger angle means a wider one.
It gives you a quick indication of how concentrated or spread out the light will be.
FWHM
Full Width at Half Maximum. The width of a beam measured between the points where intensity has fallen to 50% of its peak value.
It provides a consistent way to compare beam widths between different optics.
Beam profile
The shape and intensity distribution of the light produced by the optical system.
Two optics with a similar beam angle can still produce very different-looking distributions.
Uniformity
Describes how evenly light is distributed across the area being illuminated.
Some applications need a smooth, even distribution rather than a strong central peak.
Measuring the result
How do we talk about optical performance?
Beam shape is only part of the picture. These terms help describe how light is being transmitted, directed and delivered to the application.
Efficiency
A measure of how much of the light from the LED successfully leaves the optical system.
Higher optical efficiency generally means less light is lost before it reaches the application.
Candela (cd)
A unit of luminous intensity describing how much light is emitted in a particular direction.
It helps describe how strongly an optical system sends light towards a particular direction.
Lux (lx)
A measure of illuminance — how much light reaches a surface. One lux is one lumen per square metre.
It describes the light arriving at the target rather than simply the light leaving the source.
Controlling light
What's happening inside the optic?
An optic uses its geometry and optical properties to change the direction of light. These terms describe some of the principles and characteristics involved.
TIR
Total Internal Reflection. An optical principle used in many LED optics to redirect light from internal surfaces within the optic.
TIR allows an optic to redirect light using its own internal surfaces as part of the optical design.
Refraction
The change in direction of light as it passes from one material into another.
Refraction is one of the fundamental ways a lens changes the direction of light.
LES
Light Emitting Surface. The area of the LED from which the light is emitted.
The size and position of the emitting surface can significantly affect how an optic performs with a particular LED.
More than just transparency
Why does the optic material matter?
Optical materials have different properties, so material selection isn't simply a question of which one transmits light. The application and its environmental and mechanical requirements also matter.
PMMA
Polymethyl methacrylate. A transparent polymer widely used for optical components because of its optical clarity and transmission.
Material choice can affect optical transmission as well as the suitability of an optic for its intended environment.
Polycarbonate (PC)
Another material commonly used for optics, often considered where properties such as impact resistance or temperature performance are important.
Choosing between optical materials involves balancing optical, mechanical and environmental requirements.
Silicone
A flexible optical material that can be useful where conventional rigid polymers are less suitable, particularly in applications involving higher temperatures or demanding environmental conditions.
Silicone can offer useful thermal and mechanical properties, making it another option when selecting the most appropriate material for an optical application.
From terminology to application
Start with what the light needs to do
Selecting an optic is rarely about maximising a single number. A useful starting point is to work from the application backwards and consider the factors that will influence the final result.
A growing reference
We'll keep adding to this guide
As we cover more optical topics, we'll add straightforward explanations here — including beam types, collimation, optical losses, LED and optic combinations, testing, measurement and practical application considerations.