D10, D50, D90, and Dmax are four important parameters used to describe particle size distribution.

They are commonly used to describe powder materials, granules, etc. They indicate the proportion of particles of different sizes in the whole particle population.

D10: It indicates that 10% of the particles are smaller than this value.

D50: Also known as the “average size”, indicates 50% of the particles are smaller than this value. D50 reflects the average particle size of the entire particle population.

D90: It indicates that 90% of the particles are smaller than this value. D90 mainly reflects the proportion of larger particles in the particle population, and can be used to assess the roughness of the population.

Dmax: It indicates the largest particle size in the particle group. Dmax can be used to determine whether large particles are compatible with the size limitations of processing equipment, or whether they might affect the performance of the final product.

A common misconception is that glow in the dark powder consists of completely uniform particles, and therefore it has a single particle size.

In reality, it is quite the opposite: since conventional production processes use sieves for physical sorting, the final product is a collection of countless particles that can pass through a specific mesh. This collection ranges from the finest to the coarsest (within a certain upper limit). Therefore, its particle size is a range of values, not a single one.

For a specific batch of luminous powder, the particle size test data (D10, D50, D90, Dmax) is a single value, because it represents the test results of that particular batch. These specific figures are used for quality control and qualification assessment of that batch.

For a particular product model, It usually use D50 (average size) to define uniform particle specifications and guarantee stability to customers.

Due to normal fluctuations in industrial production, it’s hard to guarantee an absolutely consistent D50 for every batch of product. Therefore, a reasonable range (for example, D50: 25±5μm) is used to characterize the particle size of a particular product model. This range ensures consistent and reliable performance across batches.

D10, D50, D90, and Dmax are key indicators that reflect the particle size distribution. They provide important reference data when selecting suitable luminescent powder type for end products or application scenarios.

D10: Represents the distribution of finer particles in the powder. In most applications, this data has relatively little significance when selecting glow in the dark powders.

D50: Also known as “Average Particle Size”. It is the most commonly used data for evaluating glow in the dark powder particle size. In most applications, D50 is a sufficient reference.

D90 & Dmax: Reflect the large particles size in the powder. In processes with strict particle size requirements (such as ultra-thin coatings, fiber drawing, and precision spraying), or in products with thinner structures (such as blow-molded plastic straws), D90 and Dmax are particularly important. These values can directly affect the smoothness of the product surface, the overall structural performance, and the stability of the production process.

To achieve a better luminous effect in the end product, particle size range is also an important factor.

The difference between D10 and D90 reflects the width of the particle size distribution. A smaller value corresponds to a narrower range of particle sizes. A narrower distribution enables the luminous particles to mix more uniformly with the liquid medium, which in turn improves coverage and yields a clearer, more translucent luminescent effect in the final product. Conversely, a larger D10-D90 difference may adversely affect both the production process and the performance of the end product.

For example, when used in coatings, an excessively wide particle size range may cause uneven luminescence, and it may also affect the stability of the coating, making it more prone to cracking due to uneven stress distribution during curing.

Building on the above considerations, we have focused our R&D efforts on refining particle size control. This has allowed us to utilize our unique technical capabilities — a core strength of our company — to successfully narrow the particle size range to an exceptional degree.

The following chart compares the particle sizes parameters of ultra-fine 10μm particles between our products and others (samples are from materials used in actual customer production):

The resolution of the testing equipment significantly affects the accuracy of particle size measurements. High sensitivity and stability are essential to ensure consistent and reliable results.

High-resolution equipment can distinguish particle size more accurately, and deliver more stable consistency across repeated measurements. In contrast, lower-resolution instruments can not clearly differentiate similarly sized particles. When multiple measurements are taken on the same batch, particles of different sizes are easily grouped into the same category, resulting in poor repeatability of the results.

Moreover, higher-sensitivity devices are better at detecting both fine and coarse particles. Lower-sensitivity equipment are less responsive and have difficulty detecting certain particles, potentially resulting in overestimation, omission of larger particles, and overall less accurate measurements.

Comparing particle size data across different brands may not accurately reflect the actual particle size distribution. Such direct comparisons tend to be inaccurate and offer limited reference value. The reasons are as follows:

(1) Different manufacturers use different testing equipment and methods, which may lead to inconsistent and incomparable results.

(2) Even if the average particle size (D50) of some products appears similar, their actual distribution ranges may differ significantly. This will bring notable variations in the luminescence performance and visual effects of the final product.

Therefore, it is recommended not to rely only on particle size test reports for oowder type selection. Instead, checking the actual luminescent performance of end product should be used as the final decision-making basis.

(1) Particle Size Categories of GlowUp Glow in the Dark Powder

Usually we divide luminous powder into 3 categories according to the average particle size (D50)

• Ultra-fine (<15μm): Suitable for special processes or ultra-fine product structures with extremely high particle size requirements, such as ultra-fine coatings and precision spraying.
• Regular (20-30μm~70-80μm): The most widely used type, applicable to paints and coatings, printing inks, plastic products, art pigments, toys, accessories, jewelry, and more.
• Large Particle (>100μm): Commonly used for glass and ceramic sintering, or for special surface decoration.

(2) How Different Particle Sizes Affect the Practical Use of Glow in the Dark Powder?

• Process Compatibility: An unsuitable particle size can affect the production process of end products. For example, in screen printing, too many large particles may cause excessive residue on the mesh; in spray coating, large particles can clog the spray gun nozzle, leading to frequent cleaning. Therefore, the particle size should be selected according to the production equipment or process requirements.
• Brightness: Larger particles generally result in higher powder brightness, while smaller sizes emit lower brightness. However, the brightness of the end product is not only affected by the powder brightness itself, but also by the coverage of the powder particles.
• Coverage and Uniformity: The narrower the particle size range, the higher the coverage. Large particles have higher brightness but may produce uneven luminescence in thin layers. Small particles provide better coverage, resulting in a more uniform and translucent glow (as shown in the picture).

(3) How GlowUp® Ensures Particle Size Stability

To ensure highly reliable particle size performance and batch-to-batch consistency, GlowUp® has established a full-process quality control system from raw materials to finished products, including the following measures:

• Precision Instrument Testing: We use the high-precision laser particle size analyzer Omec LS-609 for particle size measurement. This equipment offers excellent resolution and sensitivity, accurately capturing the distribution of particles of different sizes. Each batch undergoes no fewer than 3–5 repeated tests to ensure data reliability and result stability.
• Strict Raw Material Control: We carefully select suppliers and strengthen raw material quality evaluation. All raw materials are tested before storage to ensure they meet particle size and related quality requirements, guaranteeing stable product quality from the source.
• Production Process Monitoring: Key process parameters such as grinding and sieving are monitored and adjusted in real time during production, ensuring each stage remains under control and preventing batch deviations.
• Batch Documentation and Traceability: We maintain independent records for each customer and retain samples for every batch. When a customer places a repeat order, we review historical test records or compare retained samples to ensure that the delivered product maintains consistent particle size distribution with previous batches, achieving reliable traceability and consistent quality.

Through these measures, GlowUp® is committed to providing customers with products that consistently feature highly stable particle sizes.