Why 365nm uv is the most effective wavelength for Photocatalytic Air Purifier ?

Why 365nm UVA LED Is Widely Used in Photocatalytic Air Purifiers

Photocatalytic air purification is becoming an interesting solution for removing formaldehyde, VOCs and other organic pollutants from indoor air. In many photocatalytic air purifier designs, 365nm UVA LEDs are used as the light source to activate the photocatalyst.

But why 365nm? Why not 395nm, or even a shorter UVC wavelength?

The answer is not simply that shorter wavelengths have more energy. The performance of a photocatalytic system depends on the relationship between the UV wavelength, photocatalyst, optical power, catalyst surface and overall reactor design.

1. 365nm Provides Enough Energy to Activate TiO₂

Titanium dioxide (TiO₂) is one of the most widely used photocatalytic materials.

When TiO₂ is exposed to suitable UV light, photons can excite electrons from the valence band to the conduction band. This creates electron-hole pairs that can participate in surface reactions.

A 365nm photon has an energy of approximately 3.40eV, which is sufficient to activate conventional TiO₂ photocatalysts.

In simple terms:

365nm UVA → TiO₂ activation → electron-hole pairs → reactive oxygen species → pollutant degradation

This is the basic mechanism behind TiO₂-based photocatalytic air purification.

2. Why 365nm Instead of 395nm?

395nm UVA LEDs are also commonly available and are often less expensive. However, 365nm provides higher photon energy.

The photon energy can be estimated from:

E = 1240 / λ

Therefore:

365nm ≈ 3.40eV

385nm ≈ 3.22eV

395nm ≈ 3.14eV

As the wavelength becomes longer, photon energy decreases.

Depending on the photocatalyst being used, moving too far toward the long-wavelength side can reduce the efficiency of photocatalyst excitation. This is one reason why 365nm is frequently selected when TiO₂ is the main photocatalytic material.

However, this does not mean that 365nm is automatically the best wavelength for every photocatalytic coating. The absorption characteristics of the actual catalyst should always be considered.

3. What Happens After TiO₂ Is Activated?

After absorbing UV photons, TiO₂ generates electrons and holes.

These charge carriers can react with oxygen and water on the catalyst surface and form reactive oxygen species, including hydroxyl radicals and superoxide-related species.

These highly reactive species can attack organic pollutants adsorbed on the catalyst surface.

For example, formaldehyde can be gradually oxidized through intermediate compounds and ultimately converted mainly into carbon dioxide and water under suitable conditions.

This is why photocatalytic air purification is different from simply trapping pollutants with a filter.

A conventional filter mainly captures particles or adsorbs certain gases. A photocatalytic system is designed to promote chemical reactions that break down organic pollutants.

4. UVA and UVC Have Different Jobs

One common misunderstanding is that UVC should always be better because it has higher photon energy.

In an air purifier, however, UVA photocatalysis and UVC sterilization can serve different purposes.

365nm UVA is commonly used to activate the photocatalyst.

UVC around 265–280nm is commonly used for direct microbial inactivation.

UVC can damage the DNA or RNA of microorganisms, while UVA can provide the energy needed for photocatalytic reactions on a TiO₂ surface.

For this reason, combining UVA and UVC can be attractive in some air purification designs.

The two wavelengths do not necessarily compete with each other. They can perform different functions within the same system.

5. Optical Power Is Just as Important as Wavelength

Choosing the correct wavelength is only the first step.

In practical product development, the available optical power reaching the photocatalyst is also very important.

A 365nm LED with insufficient optical power may not provide enough photons to achieve the desired reaction rate. On the other hand, simply increasing LED power does not guarantee a proportional improvement in purification performance.

The actual result depends on several factors:

UV irradiance on the catalyst

LED optical efficiency

distance between LED and catalyst

catalyst coating thickness

catalyst surface area

air flow rate

pollutant concentration

reactor structure

temperature and humidity

This is why an effective photocatalytic air purifier needs to be designed as a complete system rather than simply selecting a high-power UV LED.

6. Why 365nm UVA LEDs Are Attractive for LED-Based Systems

From an LED engineering perspective, 365nm is also a practical wavelength for compact photocatalytic equipment.

Compared with conventional UV lamps, UV LEDs can offer several advantages:

compact size

instant start-up

good controllability

low mercury-related environmental concerns

easy electronic dimming and control

flexible mechanical design

long operating life when properly cooled

For air purifier manufacturers, this makes UVA LEDs easier to integrate into compact modules and customized optical structures.

The LED package is also important. UV LEDs used inside air purification equipment may operate continuously for long periods, so thermal management, optical output stability and package reliability should not be overlooked.

7. 365nm Is Not a Universal Answer

It is important not to treat 365nm as a universal optimum.

Different photocatalysts have different spectral responses. Modified TiO₂, doped photocatalysts and other semiconductor materials may respond differently to UV wavelengths.

Therefore, when developing a new photocatalytic air purifier, the better approach is to test the actual combination of:

UV wavelength + optical power + photocatalyst + airflow + reactor design

rather than selecting a wavelength based only on theoretical photon energy.

For TiO₂-based photocatalytic systems, however, 365nm UVA remains a widely used and practical choice because it provides sufficient photon energy while working well with common UV LED technology.

Conclusion

The reason 365nm UVA LEDs are widely used in photocatalytic air purifiers is not simply because they are "stronger" than longer-wavelength UV LEDs.

The key is the match between the 365nm spectrum and the photocatalyst's photoactivation characteristics.

When the right wavelength is combined with sufficient optical irradiance, an appropriate photocatalytic coating and a well-designed airflow path, the UV LED can help generate reactive oxygen species that contribute to the degradation of formaldehyde and other organic pollutants.

For this reason, 365nm UVA is often a practical starting point for TiO₂-based photocatalytic air purification, while UVC can be added when direct microbial inactivation is also required.

For LED manufacturers and air purifier developers, the most important question is therefore not simply "Which UV wavelength is strongest?", but rather:

"Which wavelength, optical power and photocatalyst combination gives the best overall performance in the actual air purification system?"

 Guangmai Technology is a professional LED manufacturer established in 2009, specializing in LED packaging and custom LED solutions.

Our main products include SMD LEDs, High Power LEDs, COB LEDs, UV LEDs, IR LEDs, VCSELs, and ceramic substrate LEDs. We offer wavelengths from 200nm to 3000nm for applications such as horticulture lighting, medical devices, industrial curing, machine vision, security, and scientific research.

With advanced production equipment, strict quality control, and experienced engineering support, we provide reliable products and customized solutions to customers in more than 50 countries worldwide.

We are committed to delivering high-quality LED products, competitive pricing, and professional service to our global partners.