| The ability to adjust the color temperature of a white-light LED fixture provides benefits in a number of applications. In retail applications, for example, when a sales display is changed the color temperature can be altered to show the goods at their best. In offices, hotels and other scenarios, the color temperature can be adjusted throughout the day to optimize comfort, productivity and well being.
The usual method to achieve an adjustable color temperature is to have an array of different LEDs, for example a mix of warm- and cool-white LEDs. These are controlled separately so that the output of each set of LEDs can be adjusted, which in turn changes the color temperature of the mixed light from the fixture.
A new approach by Sharp is to build a compact LED module that emits warm and cold white light at the same time. The Tiger Zenigata array can be adjusted from 2700K to 5700K. Depending on the color temperature, the module emits a luminous flux of 1900 lm to 2200 lm with a power consumption of around 25W.
The Tiger name comes from the colors of the phosphor stripes on the array. A total of 168 blue LED chips are coated by strips of different blends of red and green phosphors, which create the warm or cold white light components.
The alternating strips are interconnected in two independent electrical circuits. The circuit for the 2700K component is made up of 96 chips arranged in eight parallel strips of 12 LEDs. The 5700K light component is created from 72 chips in six parallel strips.
Both electric circuits each need a forward voltage of 37V at a maximum power supply of 700 mA. By varying the current in each circuit in the range of 0 to 700 mA, any color temperature between 2700K and 5700K can be realized.
With a light-emitting surface of just 17-mm in diameter, the array has the optical characteristics of a point light source. This simplifies the design process of the optics of lighting fixtures and prevents the formation of multiple shadows which can appear with multi-dot light sources.
Sharp says that high CRI values can be achieved, reaching a maximum of 92 for cold white and up to 94 for warm white.
The Tiger Zenigata has the same form factor as Sharp’s Mega Zenigata LED arrays. The main difference is that the Tiger has four contacts (for the two circuits) instead of the usual two. Sharp says that it should be easy to adapt existing luminaire designs that currently use its fixed color-temperature arrays so that they can have color-tuning capability.
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