Are White LED Lamps and Fluorescent Lamps Similar?

See more: Capacity Profile Of Phuc Gia Laboratory Corporation

Why do we call tube lights fluorescent lamps?

Structurally, a fluorescent lamp consists of two electrodes (the sources of electrons) mounted at both ends of a glass tube, the inside of which is coated with a white powder called phosphor (or fluorescent powder). After being sealed, the air is completely evacuated from the lamp tube, and a few milligrams of mercury (Hg) and a small amount of inert gas (usually Argon (Ar) or Krypton (Kr)) are injected into the tube. At this point, the lamp’s pressure is very low, nearly a vacuum. With such a structure, when connected to an electrical circuit, the electrodes will emit electrons. These electrons move inside the tube at a relatively high velocity, and along their path, they collide with the mercury atoms, causing the mercury atoms to emit light.

The argon atoms serve to “obstruct the path,” forcing the electrons to follow a zigzagging path and ultimately increasing the probability of collision between the electrons and mercury atoms inside the lamp tube, ensuring that most of the mercury atoms emit light. In the low-pressure gas, the mercury atoms emit several short wavelengths, of which 61% is radiation with a wavelength of 253.7 nm. (This is why a mercury lamp typically has a blue light). The 253.7 nm wavelength radiation interacts with the phosphor layer, causing this layer to emit visible light. Therefore, the light from a tube lamp (and a compact lamp) is actually light emitted by the phosphor layer, which is why the tube lamp is called a Fluorescent Lamp Tube (FLT) and the compact lamp should be correctly called a Compact Fluorescent Lamp (CFL). Note that, if the lamp tube were not coated with phosphor and were made of quartz (to prevent the absorption of ultraviolet rays), the aforementioned lamp would become a germicidal lamp, commonly referred to as a UV lamp or ultraviolet lamp, typically used in medical applications.

Could a white LED lamp also be called a fluorescent lamp?

The basic structure of an LED chip that emits white light. When connected to a direct current source, through a complex quantum mechanism, the InGaN semiconductor layer (a compound of Gallium, Indium, and Nitrogen) emits short-wavelength blue light. If the process stopped here, we would have an LED chip used in advertising lighting.

To achieve white light, a layer of phosphor (also called phosphorus powder) is coated onto the LED chip. With this structure, the blue radiation emitted by the LED chip is forced to pass through the phosphor layer, and upon penetrating it, the blue light excites this layer to fluoresce and emit white light. Thus, in principle, can we also call a white LED a fluorescent lamp?

So, what are the differences between fluorescent lamps and white LEDs?

We will not discuss the differences in the shape or structure of the lamp assembly but only the difference in the fluorescence mechanism, which leads to a difference in the spectrum of the two lamp types.

As mentioned, the light emission mechanism of a fluorescent lamp is emission in low-pressure gas, so its spectrum is always a characteristic line spectrum where the fluorescence emission lines are primarily distributed within the visible spectrum range. The final spectra or colors are dependent on the composition of the phosphor powder. In contrast, the light emission mechanism of the LED chip is emission in a solid powder layer (solid-state), so its spectrum (although still a line spectrum) consists of only two characteristic lines within the visible spectrum range.

A close observation of the two spectra reveals that the LED chip’s spectrum has the “appearance” of a continuous spectrum, which is why it can offer a higher Color Rendering Index (CRI) compared to the fluorescent lamp. Currently, by manufacturing rare-earth doped phosphor powders (using elements like Cerium (Ce), Neodymium (Ne), Holmium (Ho), etc.), it is possible to “fill in” the trough between the two dominant peaks in the LED spectrum. With this technique, it is easy to fine-tune the Color Rendering Index (CRI) and significantly boost the luminous efficacy of the LED chip. Today, LED chips have been developed with a Color Rendering Index (CRI) approaching 1 and a luminous efficacy reaching up to 250 lm/W, whereas the luminous efficacy of conventional fluorescent lamps typically does not exceed 100 lm/W. That is also a prominent advantage of LED technology in the field of residential lighting.

Nguồn tham khảo từ bài viết của TS. Lê Hải Hưng

For more details, please contact us at:
PHUC GIA LABORATORY CORPORATION
PHUC GIA CERTIFICATION CENTER
PHUC GIA INSPECTION TESTING CENTER

Address: ICD Long Bien, No. 01 Huynh Tan Phat, Sai Dong B Industrial Park, Long Bien Ward, Hanoi City, Vietnam.
Hotline: 0981 996 996/ 0982 996 696/ 024 7779 6696
E-mail: lab@phucgia.com.vn
Website: phucgia.com.vn
Working time: Monday to Friday 8:00 – 18:30; Saturday 8:00 – 12:00