We have fabricated white organic light-emitting diodes (OLEDs) by co-doping of red and blue phosphorescent guest emitters into the single host layer. Tris(2-phenyl-1-quinoline) iridium(III) [Ir(phq)3]and iridium(III)bis[(4,6-di-fluorophenyl)-pyridinato-N,C2`]picolinate (FIrpic) were used as red and blue dopants, respectively. The effects of dopant concentration on the emission, carrier conduction and external quantum efficiency characteristics of the devices were investigated. The emissions on the guest emitters were attributed to the energy transfer to the guest emitters and direct excitation by trapping of the carriers on the guest molecules. The white OLED with 5% FIrpic and 2% Ir(phq)3 exhibited a maximum external quantum efficiency of 19.9% and a maximum current efficiency of 45.2 cd/A.

We have fabricated white organic light-emitting diodes (OLEDs) using several thicknesses ofelectron-transport layer. The multi-emission layer structure doped with red and blue phosphorescent guestemitters was used for achieving white emission. 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) wasused as an electron-transport layer. The thickness of BCP layer was varied to be 20, 55, and 120 nm. The current efficiency, emission and recombination characteristics of multi-layer white OLEDs wereinvestigated. The BCP layer thickness variation results in the shift of emission spectrum due to therecombination zone shift. As the BCP layer thickness increases, the recombination zone shifts toward theelectron-transport layer/emission-layer interface. The white OLED with a 55 nm thick BCP layerexhibited a maximum current efficiency of 40.9 cd/A.

White light emitting diode (LED) determined the most appropriate color temperature in reading lighting evaluated fatigue degree of eye according to color temperature. The eye fatigue degrees are determined by brightness and color temperature. Therefore, we measured the results of eyes test according to the change of color temperature and brightness. Experiments except for astigmatic corrected visual acuity of 0.8 more and age 20 to 25 years old, male and female college students was conducted in 100 patients. And constant illumination conditions, visual acuity was measured by varying the color temperature. The optometry at 10 minutes in the darkroom adapted eye. And then the temperature of 25±3 degrees, the humidity was carried out at 50±5%. As a result of typical color temperature of white light (5,600 K) has identification of the readability.