In the field of luminescent powder, besides the formulation affecting brightness and afterglow time, another crucial parameter is the particle size. Luminescent powder particles are typically measured in micrometers (μm). Currently, products on the market range in particle size from 2-3 μm to 1500-1800 μm. Different particle sizes are closely related to both the brightness of the powder itself and the luminous effect after application to the final product.

Luminescent powder particles are mainly divided into the following three categories:

• Large Particles: These typically refer to particles with an average size of 100 μm to 1500-1800 μm, generally suitable for high-temperature applications such as glass and ceramics.
• Regular Particles: These typically refer to an average size of 20-30 μm to 70-80 μm, covering most applications, such as safety and decorative paints, screen printing, and plastic injection molding etc,.
• Ultra-Fine Particles: These typically refer to an average size of approximately 2-3μm to 10-15μm, suitable for ultra-thin coatings, ultra-fine spraying, and special printing applications.

• Larger particles generally result in higher brightness.

The luminescence principle of photoluminescent powder involves storing surrounding photons through numerous grooves on the particle surface. These photons are then released in darkness, thus emitting light. Larger photoluminescent particles have a larger surface area and more grooves, allowing to store more photons. Therefore, they exhibit higher brightness and longer-lasting emission in the dark. Thus, a key characteristic of photoluminescent powder is that, with the same formulation, larger particles result in higher brightness and longer afterglow time.

• Using larger particles does not necessarily result in a brighter end-product.

The core reason is that smaller-particles has a higher coverage rate than larger ones. This is analogous to laying basketballs and ping-pong balls on different surfaces; the ping-pong balls create much smaller gaps between the particles, which do not emit light in the dark. Meanwhile, smaller particles are closer to each other, causing light emitted by each particle to refract and reflect, further enhancing the overall luminous effect. Therefore, choosing slightly smaller particles allows for more even coverage of the luminescent powder, resulting in a superior luminous effect.

When comparing luminescent powders from different suppliers, customers often use powder brightness as the sole criterion. If two products have the same average particle size (D50), and supplier A’s powder brightness is higher than supplier B’s, customers often assume that supplier A’s product is of superior quality.

This judgment has some merit, but in practice, the opposite may occur: after using both luminescent powders in a final product, supplier B’s product may produce a better luminous effect. The core reason is that even with the same average particle size, the particle size distribution can differ between suppliers. Supplier A’s luminescent powder has a wider particle size distribution and a higher proportion of large particles, making the powder itself appear brighter. Supplier B’s product, on the other hand, has a more uniform particle distribution. Although the powder itself is slightly less bright, it offers better coverage and dispersion when applied to the product, resulting in more transparent luminescence and a more stable visual effect in the final product.

Therefore, selecting luminescent powder should not only focus on observing the brightness of the powder itself, but more importantly, on conducting sample testing. Only through real application can its true brightness, transparency, and uniformity be observed. This process enables an accurate evaluation and reliable material selection, which is essential for creating a superior end product.