Many people are informed that “luminous pigments can glow for 8-12 hours,” but when they receive samples, they find that the glow duration is much shorter. Why does this happen? Typically, the statement “glows for 8-12 hours” comes with certain conditions. Firstly, it usually refers to naturally fired luminous pigments like yellow-green, blue-green, and sky-blue, which have the longest glow durations. Secondly, this assumes that the pigments are fully charged (under direct sunlight for 10-15 minutes) and observed in a completely dark room (no windows, door tightly closed). Without adequate charging and in the presence of ambient light, the perceived glow duration is significantly shorter.

Below, we will detail the most common factors affecting glow duration:

Luminous pigments work by absorbing and storing photons from a light source and then emitting them in the dark. Therefore, under the same light source, the longer the charging time, the more photons the pigment absorbs and stores, leading to a longer glow duration in the dark.

The effectiveness of luminous pigments varies significantly depending on the environment. The darker the surroundings, the more noticeable the effect. Since the glow is faint, any surrounding light will overshadow it, making it difficult for the human eye to perceive.

• Outdoor Environment: In outdoor settings, if there are many street lights, neon signs, etc., the glow effect will be weak. Such environments are not suitable for luminous materials. For example, luminous road paints are unsuitable for city roads filled with streetlights and are more appropriate for rural roads without electric facilities.
• Indoor Environment: In a completely dark room, even faint light can be captured by the human eye, allowing the luminous pigment to fully display its effectiveness, making the glow duration seem longer.

Different colors of luminous pigments have varying glow durations. The longest-lasting are the natural colors, including yellow-green and blue-green. When fully charged, yellow-green and blue-green pigments have the highest brightness and longest glow duration, typically 8-12 hours. Sky-blue has a slightly weaker glow and shorter duration than yellow-green and blue-green.

Dyed luminous pigments, which have daytime colors, are made by mixing natural colors with dyed fluorescent pigments. Fluorescent pigments belong to solid colors and cover part of the luminous material, resulting in a shorter glow duration. Some last 4-6 hours, some 2-4 hours, and some only around an hour.

There is also a series of orange-red luminous pigments, which are expensive due to the complex production process but have a shorter glow duration, usually only around 10 minutes to half an hour.

Other factors, such as the strength of the light source and the distance between the light source and the luminous pigment, also affect glow duration. For the same charging time, using a UV lamp (black light) will result in a longer glow duration than using an LED light because the UV lamp’s energy is higher, allowing the luminous pigment to absorb and store more photons in the same amount of time. If using a light source with the same energy, the closer the distance to the light source, the more photons are absorbed, leading to a longer glow duration.

In actual applications, regardless of the glow duration promised, it is challenging to ensure it will meet your specific needs. Suppliers do not know the specific environmental conditions of the user, and brightness is a subjective perception with no standard measure. The best approach is to obtain several samples and observe them in your application scenario. Experienced suppliers can provide suggestions and recommendations based on your product and usage scenarios, helping to avoid misunderstandings and reduce potential issues.

Additional Note: Some suppliers provide TDS showing “Afterglow time till 0.3mcd/㎡ is 240 hours.” The definition of “Visible Light” (0.3mcd/㎡) is from the European Standard DIN67510 for phosphorescent materials. In a completely dark laboratory, with a candle as a light source and the eye one meter away, the minimum brightness visible is 0.3mcd/㎡. This data is crucial for applications such as safety signs and emergency guidance systems. For everyday consumer products, however, personal observation of samples may be more practical and closely aligned with actual needs.