Why isn’t my glow in the dark mica powder as bright and long as it should be?

I purchased glow in the dark mica powder from different manufacturers. They said it could emit light for up to 8 hours. However, it only gave light for 1-2 hours after I used it. Is this because the item I bought is of poor quality?
Jeff.Chen
Jeff.Chen

Bachelor's Degree in Materials Science and Engineering, Hubei University of Technology

Before we answer your question, it’s important to clarify some basic concepts about glow in the dark mica powder. The brightness of a material is expressed in cd/㎡ or mcd/㎡. These two units differ by a factor of a thousand. When it comes to measuring the brightness of glow in the dark mica powder, it’s generally done in mcd/㎡.

In simpler terms, the process of glow in the dark mica powder emitting light involves storing the surrounding light and releasing it when there is no light in the surrounding environment. Therefore, if you want the glow in the dark mica powder to shine in the dark, you need an excitation light source to illuminate the glow in the dark mica powder for a period of time.

When the excitation light source stops shining, the luminous brightness of the glow in the dark mica powder reaches its highest point, but it typically doesn’t exceed 20cd/㎡. To put this into perspective, indoor lighting at night is generally around 100-1000cd/㎡.

The brightness attenuation characteristic of glow in the dark mica powder is that it exhibits a cliff-like attenuation within one hour after the excitation light source stops shining. After just 10 minutes, its brightness decreases to only 100-500mcd/㎡. After one hour, it drops to 10-100mcd/㎡, which is only one percent of the initial brightness. In a partially lit room, it would be difficult to see glow in the dark mica powder glowing at this point.

So according to this characteristic, does the glow in the dark mica powder quickly stop emitting light?

Actually, no. The brightness of glow in the dark mica powder rapidly decays for the first hour, but then the rate of decay slows down significantly. After ten hours, it typically maintains a brightness of 2-8mcd/㎡. The weakest light visible to the human eye in complete darkness is 0.32 mcd/㎡, and it usually takes over 10,000 minutes for the brightness of the glow in the dark mica powder to fall below this value.

This means that after the excitation light source stops shining, glow in the dark mica powder can emit light continuously for 10,000 minutes or 166.67 hours. To see the light from the glow in the dark mica powder, it is necessary to be in total darkness at this time. Seeing the glow of the powder after an hour becomes hard when exposed to the surrounding light.

Previously, manufacturers would introduce glow in the dark mica powders that could emit light for 8-10 hours to distinguish them from zinc sulfide powders that only glow for an hour. However, to accurately present and benefit from widespread testing, we now use 1-hour data to highlight the differences between these powders. Additionally, since the unit for indicating the brightness is large (cd/㎡), we typically use a smaller unit (mcd/㎡) to measure glow in the dark mica powders.

Typically, the brightness of glow in the dark mica powder within the first hour ranges between 10-100mcd/㎡, and this brightness varies depending on the particle size and quality level of the product.

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