Indirect Estimation of Absorbed Infrared LED Radiant Power Using Contactless Thermal Sensing

Area of Science:

• Optoelectronics
• Thermal Engineering
• Measurement Science

Background:

• Accurate characterization of low-power near-infrared (NIR) Light Emitting Diodes (LEDs) is often hindered by the high cost of radiometric equipment.
• Existing methods limit accessibility for broader research and development in NIR applications.

Purpose of the Study:

• To develop and validate a cost-effective, indirect method for the comparative characterization of low-power NIR LEDs.
• To enable wider accessibility to NIR LED characterization using readily available components.

Main Methods:

• Utilized a thermal response approach monitoring black-coated aluminum targets with a contactless temperature sensor (MLX90614) and ESP32 acquisition system.
• Employed a steady-state energy-balance model incorporating convective and radiative heat transfer to estimate absorbed optical power.
• Derived geometry-dependent effective coefficients for 10 mm and 15 mm diameter targets.

Main Results:

• Demonstrated a linear relationship between absorbed power and drive/electrical input power for 850 nm and 940 nm LEDs (R² > 0.995).
• Observed higher capture ratios with 15 mm targets (10.4-11.9%) compared to 10 mm targets (8.4-9.4%).
• Achieved measurement uncertainty below 25% within recommended operating ranges (≥70 mA for 10 mm, ≥80 mA for 15 mm targets).

Conclusions:

• The proposed low-cost platform provides a reliable method for comparative characterization of low-power NIR LEDs.
• This indirect method leverages thermal sensing and readily available components, enhancing accessibility for NIR emitter analysis.