We compiled a list of frequently asked questions for using the Lepton camera. If you have a question that’s not answered here, you can ask in the forum, or contact our support team at lepton.support@flir.com.


What is Lepton and should I be using Lepton vs. other FLIR products?

Lepton is not a finished good product such as our A-series or research cameras which are typically used for automation or research and development.  As such, while there is hardware for fast testing of Lepton (Lepton Breakout Board, PureThermal 2 board) Lepton itself is not a completed system.  People looking to test Lepton are looking for an inexpensive, high performing, lower cost thermal module to incorporate into a high volume system or finished product for resale, such as a smartphone or smart appliance.  Lepton requires quite a bit of understanding of thermal system design, mechanical, electrical, and software design and should not be purchased to “save money” from buying a more expensive, more capable finished solution from FLIR’s other segments.

Can I integrate the breakout board into my final product?

Both breakout boards offered by FLIR, PN 250-0587-00 and the breakout board V2.0, PN 500-0577-00 are not designed or qualified for embedded production hardware.  The breakout boards are designed for easy prototyping, testing, evaluation of the Lepton module only.

Can I use my Lepton for underwater applications?

Due to the nature of infrared light, IR receivers cannot be feasibly detect them underwater.

Can I house the Lepton in a chamber?

It is highly recommended that the final product design around the Lepton incorporates a housing and a sealed protective window in front of the Lepton module as the module itself is not sealed.  Since the Lepton is a LWIR (7-14 micron) sensor typical protective window material such as glass will not work.  Materials such as Germanium, types of silicon, chalcogenide that are transmissive in the specific wavelength are available through many optic suppliers. For best results AR/DLC coatings and window transmission of 80% should be used.

What is the difference between a shuttered and non-shuttered Lepton?

  • A shuttered Lepton will perform flat field corrections (FFCs) by default without any I2C commands from the user.  
  • With a non-shuttered Lepton, you will have to command an FFC on your own against a uniform surface that has a high emissivity.
  • For most applications the use of a shutter is necessary as uncooled cameras exhibit sensor drift and correction of the drift is necessary to clean the image and retain radiometric accuracy.

Is there a shutter available for the 25-degree Lepton?

No. The incorporation of an external shutter may be necessary and many third party suppliers of camera shutters can be purchased and integrated into your system design.


I’m integrating a Lepton with the option of 3.3V and 5V. Which one should I use?

You should use 3.3V.

Why does the image I get from the Lepton look distorted or grainy?

This is likely caused by the Lepton not performing a flat field correction (FFC).  Over time, environmental factors can cause the image quality to deteriorate and the FFC recalibrates accordingly.  A shuttered Lepton will perform an FFC with its shutter by default, while a non-shuttered Lepton’s FFC must be done manually.

How can I get colors in my Lepton image?

Thermal data from the Lepton will natively be black and white.  You can use I2C to command the Lepton to return data in RGB888.  Additionally, you can have your own color mappings and map the thermal data yourself to a colorization. Colorization can be performed using Automatic Gain Control (AGC).

Why is my Lepton video feed occasionally freezing?

This is likely to be caused by the Lepton performing a flat field correction (FFC).  By default, the Lepton will perform this action to recalibrate at certain intervals.  While doing so, there will be a brief freeze in the video.

Why am I seeing a grey screen?

  • Try pushing down on the camera, ensuring that the camera is properly inserted. You will need to cycle the camera but this should fix this issue.
  • Another possibility is you are seeing the image pre-AGC.

Can I get exact calibrated temperature data with the Lepton using radiometry?

Radiometry can be performed using the Lepton 2.5 and 3.5 cameras.

They are calibrated in the factory, however using the standard settings there is between a 5-10% margin of error. Further calibration can be performed, however this can be a challenging process and requires modifying values based on the type of surface you’ll be measuring the temperature of.

How can I connect my Lepton with MIPI?

MIPI is not currently supported for the Lepton.  Please use SPI to interface with the Lepton.

Lepton SDK

What is the Lepton SDK?

The FLIR Lepton SDK provides an API for user programs to easily communicate with the Lepton Command and Control Interface (CCI).  No imaging functions are provided.  The CCI interface uses I2C protocol as described in the Lepton Software Interface Description Document and the Lepton Engineering Datasheet.  For systems using a different operating system or different low level I2C hardware, some “porting” work will need to be provided by the user.

How do I change the power-on defaults to do things such as disabling flat field corrections (FFC)?

The Lepton receives commands from the master devices via I2C.  A Lepton SDK is available to help run these commands.

When I bring a hot object into the Lepton’s frame, everything around it darkens. How can I stop this?

The standard output of Lepton requires the user to perform their own AGC (Automatic Gain Control) algorithm from the 14 bit output into the display format (usually 8 bits).  Examples of various AGC algorithms can be found in the engineering document for Lepton.  Switching the Lepton into the RGB888 mode through the I2C command will provide a basic min/max AGC converting the 14 bits into 8 bits across the entire scene.  However, the internal RGB88 mode does not do a good job if you are looking to extract contrast between hot and cold objects and yet capture medium objects.  It is recommended that for production hardware the user creates their own AGC ideal for their application.

How can I get the Lepton to return a temperature reading?

The best way is to use a radiometrically calibrated Lepton camera. Either a Lepton 2.5 or 3.5 would work. These are calibrated during production and the SDKs provide functions that allow you to grab temperature readings.

I’ve lost sync with my VoSPI packets. How can I programmatically resynchronize sync?

  • Deassert chip-select and set the serial clock to idle for at least 185 milliseconds.
  • Reassert chip-select and enable the serial clock.
  • Now read the packets until a non-discard packet is identified.

Why are I2C commands not working when I send the Lepton commands after it starts up?

Please check your I2C connection.  Additionally, you should wait for 5 seconds after the Lepton is powered before it is ready to accept I2C commands.

Why won't the .dll files I downloaded as part of the SDK work?

DLL files downloaded from online may be being blocked by the operating system. You will need to open the properties of the DLL file, press unblock and then apply.

See the following time-stamped video to see the DLLs being unblocked: https://youtu.be/egw4Co-ICi4?t=135