LED Technology
Terms related to measurements
FWTM
Full Width Tenth Maximum – 10% (D10) for a light beam is a measurement of the beam’s width at the point where its brightness reaches 10% of its maximum, indicating its width at that intensity level.
FWHM 2 Particular cases
Some manufacturers provide comprehensive information about the PCB-to-LES distance, but it is hidden. In that case, here are the steps you can follow to find this information:
2a. Start by downloading the LED ray file from the manufacturer’s website. This is typically a large ZIP file – often over 100MB. Most suppliers offer the ray file in different formats; for optical simulations, choose either the TracePro or LightTools format, depending on the software you’re using. 2b. Open the “…_info.pdf” file in the
ZIP file.
2c. Once you’ve opened the ray file documentation, here’s what to look for: on the first page, you’ll usually find a diagram showing the origin of the LED package. In this case, the origin is located directly on the PCB, which is not always true – sometimes it might be defined elsewhere, depending on the LED design.
2d. Then, moving to the second page, you should find the coordinates for the “virtual focus”, which represents the Light Emitting
Surface (LES). In our example, it’s located at 0.958465 mm from the origin. With these two pieces of information, we can now easily calculate the PCB-to-LES distance: it’s simply 0.958465 mm in this case.
Optimising optical alignment: don’t overlook the holder Now you know how to fi nd this key information for your LED project design. Keep in mind, though, that other factors can
also play a crucial role in the success of your optical setup. One common example is the integration of a holder, which can signifi cantly impact the optimal focus positioning of your collimator. Achieving an optimal focus position of the lens is the key factor for a successful LED/collimator integration. For more information, reach out to LED optics manufacturer Gaggione.
https://www.optic-gaggione.com
Full Width Half Maximum – 50% (D50) for a light beam is a measurement of the beam’s width at the point where its brightness reaches half (50%) of its maximum intensity, providing an indication of its width at that brightness level.
EFFICACY
Luminous intensity (expressed in candelas) divided by the number of lumens emitted by the LED (expressed in lumens). The unit is cd/lm.
LOR
The Light Output Ratio is the number of lumens returned by the optics, divided by the number of lumens emitted by the light source. In other words, it’s the overall transmission of the lens. It’s a percentage that varies according to the lens.
IES
The IES file is a photometric file typically used to describe the light distribution from any optic, lighting fixture or source.
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www.cieonline.co.uk Components in Electronics February 2026 35
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