Energy Efficiency Considerations of Important Luminescent Devices

In general, the luminescent materials applied operate at physical limits, in terms of absorption of the exciting radiation and the quantum efficiency (number of visible photons generated divided by the number of photons absorbed) with which lumi­nescence is generated. In cathode-ray tubes, the energy efficiency of the phosphors used is of the order of 20% [5.225]. In plasma display panels, fluorescent lamps and LEDs, the quantum efficiency amounts to about 100% and the absorption coefficient is also very high. Nevertheless, the energy efficiency ofluminescent devices is rather low, when the energy loss is taken into account (Table 5.22). The phosphor energy loss factor in Table 5.22 is mainly determined by the Stokes Shift (the difference in photon energy of radiation absorbed and radiation emitted). This results in energy loss, which can be significant, even when the quantum efficiency is 100%.

Tab. 5.22: Energy efficiencies of important luminescent devices and a breakdown into the most important energy loss factors.


Cathode-ray tube

Plasma display panel



Phosphor — converted LED lamp






efficiency (%)

fluorescent: 25

Compact: 15

Major energy

Shadow mask:

Discharge: 90

Phosphors: 55

LED: 70

loss factors


Phosphors: 70

Discharge: 30

Phosphors: 25

Phosphors: 80


Deflection yoke:

Discharge: 20



It is observed that, although the phosphors operate at physical limits, nevertheless the energy efficiency of the devices is rather low, especially in display applications.


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