Point Source Emitter LED Technology – Improved Accuracy and Resolution for Sensor Applications

Table of Contents

Point Source Emitter
Spectrum Bandwidth for Point Source Emitters
Viewing Angle For Point Source Emitters


Light Emitting Diodes (LEDs) have been in existence for several decades. In many devices LEDs are used as illumination products, like lighting components, and indicators. LEDs, as a "green" light source, provide efficient light and longer service life for many applications. However the conventional LEDs are not suitable for special applications. Point Source Emitters (PSEs) provide an alternative for applications requiring precise light beams, including medical fiber, machine vision, and encoders.

Point Source Emitter

Point Source Emitter is a semiconductor diode that has a structure similar to that of a conventional LED. However, light emission takes place through a circular area - 25-150 µm in diameter - and the produced light is visible as a "spot." Extremely narrow and parallel viewing angles are developed by this light. These characteristics are appropriate for applications requiring lower power and a near parallel light source, in comparison with laser diodes.

A side view structure of a conventional LED and PSE is depicted in Figure 1. The first difference in these structures is the emitting light direction. Light from the standard LED is transmitted to the side. The conventional LEDs require a reflective cavity to force the light from side to top in order to refocus the direction of the light. This can result in power dissipation, light output loss, and variations in the viewing angle, and the final output light beam. In PSEs light is emitted to the upper surface through a window or an aperture on the top of the structure.

Figure 1. Side View Structure of Standard LED and Point Source Emitter. a). Standard LED Structure (b). Marktech Point Source Emitter Structure

The cathode contact position is the second difference of the structures. The standard LED’s cathode contact pad is usually found in the center of the structure, which is capable of blocking the light output due to the top wire bond. PSE's resolve this issue by positioning the cathode contact wire bond at the aperture window’s side, removing dark spots and obstacles (Figure 2). The light emitted from the conventional LED (left in Figure 2) has a number of dark spots because of the bonding pad, obstruction from the wire bond and from the reflector cup (Figure 3). Point source emitter (right in Figure 2) provides an accurate, precise and narrow beam without any dark spots.

Figure 2. Lighting Comparison of Standard LED and Point Source Emitter. Left is standard LED light output, and right is point source emitter.

Figure 3. Schematic of Standard LED.

Power output can be affected by aperture size, which is a key parameter of PSEs. A smaller aperture increases the resolution capability and leads to a lower power output. Point source emitters are available in a wide range of aperture sizes and wavelengths to meet specific application requirements. Current PSEs have wavelengths, ranging from red light (650 nm) to infrared (IR) light (880 nm) (Table 1)

Table 1. Key Parameters of PSEs

Emitting Light Color Wavelength Aperture Window Size
Red 650 nm 25 µm
Red 650 nm 80 µm
Red 650 nm 150 µm
Infrared (IR) 850 nm 50 µm
Infrared (IR) 850 nm 150 µm
Infrared (IR) 880 nm (Under Development) 50 µm
Infrared (IR) 880 nm (Under Development) 150 µm

Spectrum Bandwidth for Point Source Emitters

Standard LED emitting light is neither broadband, like a tungsten lamp, or monochromatic, like a laser, instead it exists in between the two. Therefore output light bandwidth is of immense importance for a wide variety of applications. LEDs have a spectrum bandwidth ranging from 30 - 100 nm, and PSEs provide a narrower bandwidth of 20 - 50 nm. An even narrower bandwidth is required for some special applications, for instance the image system in some microscopy applications require the emitter to produce narrow band emissions and less stray light in the test sample’s background image.

The spectrum of 880 nm PSE and 880 nm standard LED is shown in Figure 4. The blue line represents 880 nm standard LED spectrum with 60 nm bandwidth, and the red line depicts the spectrum of 880 nm PSE with a bandwidth of 40 nm, which is 20 nm less than the conventional LEDs. This proves that a tighter monochromatic beam is emitted by the PSEs when compared to the LEDs.

Figure 4. Spectrum of 880 nm standard LED and 880 nm PSE

The spectrum of 850 nm standard and narrow bandwidth PSEs is shown in Figure 5. The green light depicts 850 nm standard PSE spectrum with 40 nm bandwidth, and the orange line illustrates the spectrum of 850 nm PSE with narrow bandwidth. Typically the bandwidth of 850 nm narrow bandwidth PSEs can reach 25 nm, which can be lowered further based on the customer's requirement.

Figure 5. The spectrum of 850nm standard and narrow bandwidth PSEs

Viewing Angle For Point Source Emitters

LED viewing angle is a function of optics, package, and chip type. A viewing angle of 15° - 120° is available for standard LEDs. Point source emitters with viewing angles as narrow as 40 can be offered using special optics. There are various technologies available that can help to optimize the viewing angle including the usage of an internal ball lens or external optical glass lens. These lenses improve product reliability, and also optimize the light trace and reduce light loss. The conventional LEDs are usually encased in plastic materials or an epoxy. Premature light output degradation can occur if these encapsulants chemically react with the die. Most PSEs are wrapped in hermetically sealed housings, consisting of nitrogen or air, to achieve improved output degradation and a better life span. An example of the application of an external glass optical lens is shown is Figure 6.

Figure 6. An example of an external glass optical lens being applied

It is possible to obtain a wide range of high reliability package options, such as coaxial metal cans, hermetically sealed TO-46 and TO-18 metal cans, and ceramic surface mount packages. All of these packages contain a wide choice of lenses and package heights. Some of the available lens options are dome lens and flat glass window. Figure 7 presents some standard PSE package styles. Custom package solutions are also offered.

Figure 7. Some standard PSE package styles


  • High reliability
  • Narrow spectral bandwidth
  • Unobstructed light output
  • Flexible emission area (25 - 150 µm)
  • High temperature capability
  • Low ESD sensitivity
  • High current capability
  • Fiber optic cable can be placed close to the die
  • No side light emissions
  • Well defined beam for high accuracy


  • Food inspection
  • Encoders
  • Line sensing
  • Edge sensing
  • Instrumentation
  • Linear positioning
  • Short haul fiber
  • COB emitter module
  • Optical switches
  • Machine vision
  • Medical sensing
  • Distance and range finding indication

This information has been sourced, reviewed and adapted from materials provided by Marktech Optoelectronics.

For more information on this source, please visit Marktech Optoelectronics.

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