Incoherent Light Sources for Research and OEM Design

Incoherent light sources emit light in a broad range of wavelengths and do not have a fixed phase relationship between the emitted photons. They include incandescent lamps, discharge lamps, and light-emitting diodes (LEDs). Coherent light sources, on the other hand, emit light with a well-defined phase and polarization, and include lasers and other coherent sources. Coherent sources have unique properties such as high brightness, narrow linewidth, and long coherence length, but are more complex and expensive than incoherent sources.

The spectral properties of incoherent light sources can be characterized using spectrometers, which can measure the intensity and wavelength distribution of the emitted light. The spectral output of incoherent sources can be continuous, like in incandescent lamps, or discrete, like in discharge lamps and LEDs. The spectral bandwidth and peak intensity of the source can also depend on the temperature, pressure, or other parameters of the light-generating process. The spectral characterization of incoherent sources is important for applications such as spectroscopy, imaging, and colorimetry.

The output power of incoherent light sources can be measured using power meters or radiometers, which can quantify the total power or the power density of the emitted light. The measurement can be done either directly, by placing the sensor in the path of the light beam, or indirectly, by measuring the irradiance or illuminance of the light on a surface of known area. The output power of incoherent sources can vary depending on the input power, the efficiency of the light-generating process, and the losses in the optical system. The measurement of the output power of incoherent sources is important for applications such as photometry, radiometry, and laser safety.

The common types of incoherent light sources used in microscopy include halogen lamps, mercury arc lamps, xenon arc lamps, and LED arrays. Halogen lamps provide bright and continuous illumination in the visible range, and are widely used in brightfield and phase-contrast microscopy. Mercury arc lamps provide intense and narrow-band illumination in the UV and visible range, and are used in fluorescence and confocal microscopy. Xenon arc lamps provide high-intensity and broad-spectrum illumination in the UV and visible range, and are used in spectroscopy and imaging. LED arrays provide tunable and efficient illumination at specific wavelengths, and are used in fluorescence, multiphoton, and superresolution microscopy.

The common types of incoherent light sources used in spectroscopy include tungsten filament lamps, deuterium lamps, and xenon flash lamps. Tungsten filament lamps provide a continuous spectrum in the visible and near-IR range, and are used for general purpose spectroscopy. Deuterium lamps provide a strong emission line in the UV range, and are used for UV-Vis spectroscopy. Xenon flash lamps provide high-intensity pulses of light across the UV-Vis range, and are used in time-resolved spectroscopy and flash photolysis.

LED light sources have several advantages over other incoherent sources, including high efficiency, low power consumption, long lifetime, tunable spectrum, and fast modulation. LEDs can be fabricated to emit light at specific wavelengths or with narrow spectral bandwidths, making them suitable for applications such as fluorescence microscopy, photodynamic therapy, and colorimetry. LEDs can also be modulated at high frequencies, making them useful for time-resolved measurements and optical communication.

Broad-spectrum incoherent light sources emit light over a wide range of wavelengths, such as incandescent lamps and white LEDs. Narrow-band incoherent light sources, on the other hand, emit light at specific wavelengths or with narrow spectral bandwidths, such as mercury arc lamps and laser-driven light sources. Broad-spectrum sources are useful for applications that require illumination across a broad spectral range, such as microscopy and illumination. Narrow-band sources are useful for applications that require precise control over the spectral properties of the light, such as spectroscopy and sensing.

Radiant flux is the total power emitted by a light source, measured in watts (W). Irradiance is the power density of the light incident on a surface, measured in watts per square meter (W/m²). The irradiance at a point on a surface is proportional to the cosine of the angle between the surface normal and the direction of the incident light. The measurement of irradiance is important for applications such as photometry, radiometry, and solar energy.

Luminous flux is the total visible power emitted by a light source, measured in lumens (lm). Illuminance is the visible power density of the light incident on a surface, measured in lumens per square meter (lm/m²), also known as lux. Illuminance is a measure of the perceived brightness of the light, and depends on the spectral properties of the light and the sensitivity of the human eye. The measurement of illuminance is important for applications such as lighting design, display technology, and photobiology.

Monochromatic light consists of a single wavelength or narrow range of wavelengths, such as the emission line of a laser or the spectral line of a gas discharge lamp. Polychromatic light consists of a broad range of wavelengths, such as the emission spectrum of an incandescent lamp or the white light from the sun. The spectral properties of the light can affect the performance and accuracy of optical instruments and measurements.