Light-emitting diodes as light sources for spectroscopy: Sensitivity to temperature

Abstract

Understanding of light-emitting diode lamp behaviour is essential to support the use of these devices as illumination sources in near infrared spectroscopy. Spectral variation in light-emitting diode peak output (680, 700, 720, 735, 760, 780, 850, 880 and 940 nm) was assessed over time from power up and with variation in environmental temperature. Initial light-emitting diode power up to full intensity occurred within a measurement cycle (12 ms), then intensity decreased exponentially over approximately 6 min, a result ascribed to an increase in junction temperature as current is passed through the light-emitting diode. Some light-emitting diodes displayed start-up output characteristics on their first use, indicating the need for a short light-emitting diode ‘burn in’ period, which was less than 24 h in all cases. Increasing the ambient temperature produced a logarithmic decrease in overall intensity of the light-emitting diodes and a linear shift to longer wavelength of the peak emission. This behaviour is consistent with the observed decrease in the IAD Index (absorbance difference between 670 nm and 720 nm, A670–A720) with increased ambient temperature, as measured by an instrument utilising light-emitting diode illumination (DA Meter). Instruments using light-emitting diodes should be designed to avoid or accommodate the effect of temperature. If accommodating temperature, as light-emitting diode manufacturer specifications are broad, characterisation is recommended.

Temperature dependent photoluminescence of Cr3+ doped Sr8MgLa(PO4)7

“…The NIR LEDs possess some advantages over tungsten-halogen lamps, i.e. higher electrical to optical conversion efficiency (wall-plug efficiency ∼50%), longer lifetime (∼100 000 h), and much smaller size [5]. However, a severe drawback of NIR LEDs is the relatively narrow band emission spectrum (spectral bandwidth at 50% of maximum intensity ∼30 nm), and sensitivity to temperature and drive current in terms of intensity and peak wavelength [6,7].…”

A review of near infrared spectroscopic features of teeth, bone and artificial hydroxyapatite

“…Light emitting diode (LED) technology has advanced greatly in recent decades, with increases in LED intensity and available peak wavelengths of light emitting diodes, enabling a range of applications. 68 LED output has a full width half maximum (FWHM) of around 50 nm at 850 nm and 100 nm at 1300 nm. 69 The limiting factor is therefore detector availability rather than illumination source.…”

Two-Dimensional Transient Temperature Distribution Measurement of GaN Light-Emitting Diode Using High Speed Camera

“…The emissivity in the TI measurement is also hard to be accurately determined for various materials in GaN LED, such as the cathodes and anodes. Other reported methods like the forward voltage [5], [6], centroid wavelength [7], peak wavelength [8], full width at half maximum [9], normalized emission power [10], blue-white ratio [11], Raman spectroscopy [12], [13], bi-directional thermal resistance [14], Micro-infrared Imaging [15], etc., are generally adopted to measure the average junction temperature of GaN-based LED. Recently, our research group has carried out several studies about measuring 2D surface temperature of GaN LED based on the hyperspectral imaging technology [7], [16].…”