Nagasaki-based lighting manufacturer Inex Corp, has developed the new LED luminaires, with engineering support from Luxeon supplier Future Lighting Solutions, to replace the halogen lamps that illuminate the 200 cherry trees in Chidorigafuchi Park in Tokyo.
The trees explode with baby pink blossoms with more energy-efficient, flower-friendly solid-state floodlights built with Luxeon K2, with Thin Film Flip Chip (TFFC) LEDs from Philips Lumileds.
With hundreds of thousands of Tokyo residents flocking to Chidorigafuchi Park every spring, the trees, which are illuminated at night with halogen lamps, not only consume excessive energy but also damage the flowers with heat and ultraviolet rays.
Lighting the trees at night is essential to support the tradition of the after-dark flower viewing parties, as well as to take full advantage of the short-lived season, but the existing halogen lighting failed to fit with energy-saving initiatives launched by Tokyo governor Shintaro Ishihara, to conserve natural resources and fight global warming.
The park needed several different outdoor solid-state luminaires with light outputs as high as 2,800 lumens. Fixtures would be placed either on the ground or on a stone wall to light the trees from below. Inex developed the basic board design, but sought outside expertise on several engineering issues related to thermal management. The company also wanted to explore its LED product options, because of dissatisfaction over color inconsistencies in a previous project that utilized non-Luxeon light sources.
Youichi Oda, president of Inex, said, “We knew we had to drive whatever LED we chose, at a high current, to hit the park’s target brightness levels, but we didn’t have time for extensive prototyping. We also needed to color consistency from LED to LED.”
Future engineers solved the prototyping problem with the company’s proprietary QLED thermal simulation software, enabling rapid modeling of heat distribution as well as luminous flux, without lengthy trial-and-error design cycles. Future also recommended the use of Luxeon K2 with TFFC LEDs, because of their ability to be driven at 1,000mA, and thereby produce the required light output.
The color challenge was addressed with Future’s binning program, which offers 19 color bins for cool white Luxeon LEDs alone, to ensure color uniformity within each shipment, as well as from order to order. Future was able to guarantee supply of LEDs from several cool white color bins that met the project’s specific requirements, assuring Inex that the color of its new floodlights would not vary perceptibly.
In early 2009, the collaboration between the two companies culminated in Inex’s Sky Highbeam-X, a family of floodlights that utilizes Luxeon K2 with TFFC LEDs, along with custom-designed heat sinks, optics and drivers. The fixtures are available in both seven and 14-LED models, with special weatherproofing measures devised to protect the fixtures from rain and dust. The finished floodlights were installed in Chidorigafuchi Park between March 27 and April 10, to coincide with the annual cherry blossom festival. The fixtures are illuminated for four and half hours every night during the annual ‘hanami’ (flower viewing) season.
The Japanese custom of viewing cherry blossoms – Sakura in Japanese – dates back to before the eighth century. The Sakura blooms all over Japan from mid-January to early May, typically flowering in Tokyo in late March or early April. Visitors to Chidorigafuchi Park during the one- or two-week-long cherry blossom season are treated to vast expanses of flowering trees that can be seen from land as well as from boats traversing the moat that used to be part of the Imperial Palace grounds.
