1. Light Emission Principle
A fluorescent lamp is a typical low-pressure mercury vapor discharge light source.
Its operating principle is as follows: when the mercury vapor discharge is excited, about 90% of the power is concentrated in radiating 253.7 nm ultraviolet light. These UV photons are absorbed by the phosphor particles on the inner wall of the lamp tube and converted into soft white visible light through the photoluminescence effect. Only about 30% of the energy in a fluorescent lamp is converted into heat. Its luminous efficacy is much higher than that of incandescent lamps, featuring low energy consumption and high light output. It is widely used in lighting scenarios such as indoor offices, classrooms, and industrial plants.
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2. Core Structure
The phosphor consists of a host material and an activator. The outermost electrons of the activator atoms absorb UV photons and transition from the ground state to an excited state. Due to relaxation, the excited electrons convert a portion of their energy into lattice vibrations (thermal energy) and drop to the bottom of the excited state. The relaxed electrons then transition from the bottom of the excited state back to the ground state, emitting visible light.
(Image source: https://en.wikipedia.org/wiki/Fluorescence#/media/File:Jablonski_Diagram_of_Fluorescence_Only-en.svg)

3. Spectral Characteristics
The spectrum of a fluorescent lamp exhibits a discontinuous, multi-peak structure, characterized by sharp characteristic spectral lines of mercury atoms superimposed on the broad emission bands of the phosphor.
Emission Spectrum of Gaseous Mercury Atoms
This is directly generated by the low-pressure mercury vapor discharge inside the lamp tube, manifesting as extremely narrow and sharp energy peaks. The main characteristic wavelengths include: 404.7 nm (violet), 435.8 nm (blue), 546.1 nm (green), and 577.0 / 579.1 nm (yellow doublet).
(Image source: https://en.wikipedia.org/wiki/Fluorescent_lamp#/media/File:Fluorescent_lighting_spectrum_peaks_labeled_with_colored_peaks_added.png)

Phosphor Emission Spectrum (Broadband Continuous Spectrum)
This is generated by the photoluminescent conversion of the phosphor on the inner wall of the lamp tube, providing a continuous background energy for the spectrum:

• Energy level broadening mechanism: Lattice thermal vibrations (phonon coupling) in the solid phosphor cause the energy levels of the activator atoms to spread, broadening the originally sharp transition lines into broadband radiation.
• Multi-component synthesis: By blending tri-phosphors (red/green/blue) or various rare-earth phosphors in specific proportions, the energy gaps between the mercury spectral lines are filled, allowing flexible adjustment of the correlated color temperature (CCT) and color rendering index (CRI).

4. Common Fluorescent Lamps
Common fluorescent lamps can achieve different spectral characteristics by adjusting the phosphor materials and their proportions, fully meeting the needs of various industries such as jewelry appraisal, automotive coating inspection, textile proofing, office and retail lighting, and print packaging inspection. Building on this, the International Commission on Illumination (CIE) has standardized the spectra of some common fluorescent lamps, forming the FL series illuminants. This provides industry color matching, scientific research, and global supply chains with a set of “repeatable and calibratable” fluorescent lamp spectral benchmarks.