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What is the meaning of Luminescence?
Luminescent material absorbs energy, acts on it and then emits this as light, either immediately or over a longer period, in excess of thermal radiation. This light emission, or exitation energy (in contrast to thermal radiation), does not first contribute to the thermal energy of the compound.

What is the meaning of Fluorescence?
Light emission from a substance during the time when it is exposed to exciting radiation is called fluorescence.

What is the meaning of Phosphorescence?
The afterglow (glow in the dark) that can be detected by the human eye after the cessation of excitation is called phosphorescence.

What is the meaning of Brightness?
Brightness is another expression for the photometric term luminance. It describes the emitted luminous intensity per unit area of a light source in millicandella per square meter or foot-lamberts (1mcd/m2 = 0.2919 mft.L.)

What is the meaning of Luminous Intensity?
Luminous Intensity given in candela (cd) is that portion of the luminous flux emitted in a particular direction.

What is the meaning of Luminous Flux?
Luminous flux in the visible spectral range is radiant power rated according to its ability to produce visual sensation in the human eye. The unit is the lumen (lm).

What is the meaning of Light Output?
The Light Output may be specified in photometric or radiometric units. Photometric measurements for illumination and displays are made with respect to the visual response of the standard light-adapted human observer as determined by the CIE. Radiometric measurements describe radiated power (including the non-visible radiation) in absolute terms, such as watts per unit wavelength. They are useful for applications involving photo sensors.

What is the meaning of Radiance?
Radiometry deals with the total radiated power at all wavelengths. Radiance describes the intensity per unit area of the source of radiant energy in units of watts per unit area.

General remarks

The Interdependence of Phosphorescence and Temperature
The emission of light by a phosphor depends on temperature. When phosphors are exposed to high temperatures, they emit light very quickly but also only for a short period of time. Whereas when phosphors experience low temperatures, light emission might be very low even when the phosphors are fully charged. Therefore phosphorescent products are tested at a standard temperature of 23C.

Which factors affecting brightness are known?
Brightness depends on:
Product parameter
Phosphor Loading Weight

Film Quality
-transparency
-homogeneity
-thickness
-particle distribution
Phosphor
-efficiency
-color
-persistence

Application Parameter
Excitation Strength
-intensity
-time
Excitation Conditions
-lamp type
-distance lamp-phosphor
-illumination angle
-temperature
Detector System
-sensitivity
-special characteristics
-speed

Which chemical and physical factors affecting the light fastness are known?
- Concentration or loading weight of the dye or pigment
- Degree of aggregation of the dye and, correspondingly, particle size of the pigment
- Chemical and physical structure of the substrate
- Diffusion of volatile substances in the polymer
- Energy transfer through dye-substrate bonds and dye-substrate association
- Wavelength distribution of incident radiation
- Composition of the atmosphere, in particular the humidity and the presence of contaminants

Light fastness depends on the total system, not on the pigment or dye alone!