Abstract
In this work, a scheme of combining an aspheric reflector and a primary packaging freeform lens in phosphor-converted lighting-emitting diode (pc-LED) based lighting system design was developed. In contrast to most of previous works in which the color and illumination uniformity of the pc-LED lighting systems were improved one by one, the developed scheme can improve both indicators simultaneously. To demonstrate the feasibility of the developed design scheme, an initially designed pc-LED optical model, with an average correlated color temperature (CCT) of about 5000 K, was constructed as the light source of the illumination system. The key ingredient to the color uniformity of the illumination system was investigated at first, and then several instances with the cut-off angle ranging from 40 to 60 degrees were further discussed. Detailed analysis shows: for each case, the CCT variation decreases from over 4000 K to smaller than 300 K and the illumination uniformity increases from a very low level to better than 80% on the target region.
Highlights
Nowadays, due to excellent characteristics, such as long lifetime, energy saving, environment friendly, and high color rendering, light-emitting diodes (LEDs) have been successfully used in the area of indoor/outdoor lighting, vehicle headlights, backlight of liquid crystal display, landscape lighting, search light, and so forth [1,2,3,4]
The aspheric reflector is made by metallic material and the inside surface of it is coated with reflective material with a reflectivity of 95%. a and b represent the semi-aperture size and the depth of the reflector, respectively. φcut denotes the cut-off angle of the luminaire, it is generally given by designers according to illumination requirements. and represent the initial points of the freeform lens and the aspheric reflector, respectively. divides the surface of the lens into two parts: surface 1 (S1) and surface 2 (S2)
Simulation results show that as proper energy partition angle φc was selected for a pre-specified φcut, better than 80% illumination uniformity, smaller than 300 K correlated color temperature (CCT) variation can be obtained
Summary
Due to excellent characteristics, such as long lifetime, energy saving, environment friendly, and high color rendering, light-emitting diodes (LEDs) have been successfully used in the area of indoor/outdoor lighting, vehicle headlights, backlight of liquid crystal display, landscape lighting, search light, and so forth [1,2,3,4]. Prins et al [28, 29] proposed an inverse method for TIR collimators to achieve a uniform color spot light with prescribed intensity distribution in the far field These works were mainly devised for lighting units with small cut-off angles. The key point of this work is combining a primary packaging freeform lens and an aspheric reflector in illumination system design These two components can modulate the light energy emitted from LED to generate a light spot with uniform illuminance distribution, and mix the blue and yellow light adequately to make the light spot has a uniform color distribution. This design scheme can achieve luminaire with a specified cut-off angle within a wide cut-off angle range
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