New Industry Products

ROHM Expands its Line of Tiny Infrared LEDs for Head Mounted Displays

February 10, 2021 by Gary Elinoff

The power-frugal devices are aimed largely at use cases involving in tracking human eye movement in virtual reality and related applications

The CSL1501RW is the latest member of ROHM’s PICOLED line. The side-mounted units measure a scant 1.0x0.55mm, t=0.5mm  and draws 20% less current than competing devices. 


ROHM Expands its Line of Tiny Infrared LEDs For Head Mounted Displays Figure
Image courtesy of ROHM


Responding to a Market Need

The new CSL1501RW is proposed for applications in VR/MR/AR (Virtual Reality/Mixed Reality/Augmented Reality). This technology is rapidly being popularized by means of head-mounted displays and headsets for use in widely available gaming systems.

Mixing the real world with calculated simulations is also becoming a fact of life in many industrial, military and commercial situations as well. This has led to the exploitation of mechanisms dependent on accelerometers to detect body movements, and infrared LEDs to pin down the location that the eye is looking, and thereby what part of the real or imaginary scene is being looked at.


Ascertaining Where the Human Eye is Looking

The reader will note that this LED emits light at 860 nm, which is in the infrared (IR) region, beyond the range of human vision. Its purpose is to ascertain the position of the eye’s focus, relative to the position of, for example, a virtual reality headset or helmet that a person is wearing.

Aside for the IR transmitter, the headset has an IR receiver. As the eye’s focus moves to look at different portions of the virtual scene, the component system will track the position of the focus. The complex methodologies that underlie this capability are described in OPTICS and in Tufts.


Light Emitted Parallel to Mounting Surface

The CSL1501RW’s side-firing mechanical orientation offers enhanced design versatility that makes it well-suited to serve as a light source for eye-tracking in augmented reality and for similar applications.


ROHM Expands its Line of Tiny Infrared LEDs For Head Mounted Displays Figure
Image courtesy of ROHM


At a forward current (IF) of 37mA, the infrared LED emits 3mW of radiant energy per steradian (sr) and derates linearly to 0 mW at an IF of approximately 1mW. As per ROHM, conventional infrared LEDs need an IF of 47mA to generate the same  3mW of radiant energy per steradian.

This is an important consideration in devices like VR headsets, and translates into longer operating time between rechargings for these mobile devices.


Absolute Maximums

  • Maximum power dissipation at 25℃ is 100 mW
  • Maximum forward current at is 50 mA from -40℃ to +40℃. Then it declines linearly to 
    • 10 mA at 85℃
  • Maximum peak forward current (at 25℃ with duty 1/10, 1kHz) is 200 mA


Electrical Characteristics 

Typical values for voltage and current at 25℃ 

  • With a forward voltage of 1.4 volts, typical current will be 20 mA
  • With a forward voltage of 1.5 volts, typical current will be 30 mA


Radiant Energy Varies with Temperature 

With forward current at 30 mA, when compared to the radiant energy at 25℃

  • At -40℃, radiant intensity is 15% brighter
  • At +85℃, radiant intensity is 15% less bright


Physical and Environmental Considerations

  • The CSL1501RW1 operates over a temperature range of -40 to +85℃
  • The units are RoHS compliant