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The healthcare units require dynamic color and illuminance for multitasking and wellbeing of the patients and caregivers. This requisite could be effectively satisfied by the light emitting diode (LED)-based light source. Hence this paper presents a color characterization of multicolor LED luminaire featuring illuminance from 50 to 1200 lx and color dynamism from 2700 to 6500 K using red-green-blue-amber-cool white-neutral white LEDs. The color quality assessment is conducted for 11 illuminance levels and seven correlated color temperature. The work achieved a maximum of circadian action factor (CAF) tunability 3.9 with luminous efficacy radiation (LER) above 300 lm/W and color rendering index above 90 for all correlated color temperatures (CCTs). The prototype model designed featured a beam spreading angle of 30° and luminous efficacy of 53.8 lm/W delivering a circadian stimulus of 70% for CCTs above 4000 K and illuminance above 500 lx. The blue light hazard efficiency of radiation scored a low value of 0.22 at 5700 K, 318 lm/W. This quantifies that the designed luminaire is photobiological safe. The designed luminaire is also tested for rendering the image quality using structural similarity index. These investigations assay that the designed multicolor multichip LED luminaire replaces conventional lamps deployed for dynamic illuminance and task operation in healthcare units

In the present communication, we present results on the effect of rare-earth (RE) substitution at La-site on the structural, electrical and thermoelectric properties of La0.7−xRExSr0.3MnO3 compounds. The lattice parameters are observed to decrease with RE-doping which is attributed to the fact that the substituted RE ions (RE = Eu, Gd and Y) are smaller than that of La ion. In high temperature semiconducting regime, small polaron hopping (SPH) model is valid, whereas, variable hopping model is valid in low temperature metallic region. The resistivity in the entire temperature range follows percolation model. All the samples exhibit sign reversal in thermopower, S. From temperature dependent S data, it is seen that SPH model is applicable in high temperature regime.

The LED based dynamic lighting scheme, require compact and thermally efficient luminaire. This paper presents the thermal investigation on the conceptual design of 36 W multicolor light emitting diode (LED) luminaire. The developed prototype design includes configuration and placement of the multichip LED package, RGBW and single die amber LEDs in a 5 × 3 array on the heat sink. LED configurations with low power input are placed between the LEDs having the high power input. The proposed configuration and placement of LEDs reduces the local heat concentration in the centre region of the heat sink. The temperature of 72 °C at LED chip base plate is reduced to 32.1 °C on the heat sink surface. The numerical results are experimentally validated. The proposed method contributes to a reduction in the size of the luminaire and also enhancement of heat dissipation for improving the longevity of the multicolor based LED luminaire.