New customers often have a misunderstanding about the brightness of glow in the dark pigment. The manufacturer said that it could glow for 8 hours or more. However, why it nearly couldn’t be seen after 1-2 hours?
Let us know some basic knowledge. The unit of brightness is cd/㎡(Candela per square meter) and mcd/㎡(millimeter Candela per square meter). cd/㎡equal to 1000mcd/㎡. The light of luminous powder is usually indicated by the latter.
Directly speaking, it’s a process that glows in the dark pigment absorbs the light source. Then releases light when there is no brightness in the surrounding environment. Therefore, to make the pigment glow in the dark, it needs to incentive light sources with illuminating the pigment for a period of time.
The moment when excitation light source stops shining, the brightness of the glow in the dark pigment is the highest. But it usually no more than 20 cd/m2(reference: indoor lights in the evening is generally 100-1000 cd/m2).
The brightness attenuation feature of the luminescent powder:it appears a cliff attenuation within one hour when the excitation light source stops shining. The brightness after 10 minutes is only 100-500mcd / M2, and after one hour it is 10-100mcd / M2, which is only 1 % of the initial brightness. At this time, it is difficult for people to see the luminous powder glow in the dark room.
According to this feature, is that mean the luminescent pigment soon can’t glow?
Not really, the brightness of the glow in the dark pigment begins to decay slowly after an hour’s rapid attenuation. After ten hours, the intensity of the pigment can maintain at 2～8mcd/㎡. The minimum visible light to the human eye in total darkness conditions is 0.32 mcd/㎡. And it usually takes more than 10,000 minutes for the pigment’s brightness attenuation below this value.
That is to say the luminescent pigment can continue to glow for 10,000 minutes(166.67 hours) after the excitation light source stops shining. At this time, only in a completely dark environment we will see the light. Once there is ambient light around, it is nearly to see the bright after an hour.
In the early time, to distinguish from zinc sulfide luminous powder that can only emit light for 1 hour manufactures usually propagate the long-afterglow of glow in the dark pigment for 8-10 hours. Nowadays, with the test instrument’s application and express accurately, it is gradually replaced by one-hour data. Due to a large number of cd/m2 units, glow in the dark pigment usually uses mcd/m2.
In general, the brightness of 1 hour is between mcd/m2. However, the pigment of different particle sizes and different brightness grades are not the same.