The phrase "an external light source" is correct and usable in written English.
You can use it when referring to a light source that is not part of the immediate environment or structure, often used in contexts like photography, lighting design, or scientific experiments.
Example: "To achieve the desired effect in the photograph, we need to set up an external light source to illuminate the subject from the side."
Alternatives: "a supplementary light source" or "an outside light source".
Along with using an external light source, an external power source is also required.
The system utilises an active sensor, so it is completely independent from the requirement of an external light source (including the sun and any artificial light source).
Taking this into account, various platforms have been designed to accessorize and power an external light source with a specific wavelength needed for fluorescent sensing on paper platforms.
In the performance tests, a metal halide lamp was used as an external light source to resemble the solar visible spectral radiation.
Disinfection of the intraluminal space of single-lumen polymer tubes can be obtained by ultraviolet C (UVC) light exposure from an external light source.
Detection of bands is by fluorescence, with an external light source; photodiode detectors can be either external or microfabricated into the device.
Thus, Mr. Turrell's dazzling opening, like any external light source, cannot announce the presence of the deity.
A diffuse external light source and diffusely reflecting wall coatings were assumed.
For experiments involving motile early endosomes decorated with DidB-GFP we used four-chambered Lab-Tek coverglasses and a Leica DMI6000B inverted microscope with motorized z-focus, equipped with a Leica EL6000 external light source for epifluorescence excitation and a Semrock Brightline GFP-3035B filter set.
We present a novel system design that can generate the optimized wavelength-tunable optical pulse streams from an uncooled gain-switched Fabry Perot semiconductor laser using an optical amplifier as external light source.
Typically, laser gases are contained in cylindrical tubes and excited by an electric current or external light source, which is said to "pump" the laser.
