Solid state electronics have replaced their vacuum tube predecessors for almost five decades. However in the next decade they will be brighter, more efficient and inexpensive enough to replace conventional lighting sources (i.e. incandescent bulbs, fluorescent tubes).
Recent development in AlGaP and AlInGaP blue and green semiconductor growth technology have enabled applications where several single to several millions of these indicator LEDs can be packed together to be used in full color signs, automotive tail lambs, traffic lights etc. still the preponderance of applications require that the viewer has to look directly into the LED. This is not “SOLID STATE LIGHTING”
Artificial lighting sources share three common characteristics:
-They are rarely viewed directly: light from sources are viewed as reflection off the illuminated object.
- The unit of measure is kilo lumen or higher not mille lumen or lumen as it is incase of LEDs
-Lighting sources are pre dominantly white with CIE color coordinates, producing excellent color rendering
Today there is no such commercially using “SOLID STATE LAMP” However high power LED sources are being developed, which will evolve into lighting sources
The Promise Of Solid State Lighting
In 1999, the USA consumed 3 Trillion kWh of energy, 21% of which was used for lighting. Incandescent bulbs consumed 40% of the energy used for lighting (252 Billion kWh) to generate 15% of the total light produced. The more efficient fluorescent and discharge light sources consumed the remaining of the energy (378 Billion KWh) generating 85% of the light. At nearly $60 B/year, $12 B of which is for sources alone, the lighting market dwarfs the $3 B/year (2000) indicator LED market
With the convergence in the mid 1990s of major advances in AlInGaN and AlInGaP material technologies by the turn of the millennium LEDs were rapidly surpassing the efficiency of color filtered fluorescent light bulbs and white incandescent and halogen light bulbs. LEDs inherit other important advantages including lifetimes measured in tens of thousands of hours, ruggedness, environmental friendliness (no mercury), compact size, low operating voltages, and cool operation. Their small size allows design flexibility in the control and steering of the emitted light by utilizing sophisticated secondary optics. However, today’s lighting applications which require a light source to illuminate a desk, a screen, or a room demand not only high efficiency and long life, but also high flux, all at a low unit cost. The challenge is designing LED devices and packages that sustain two to three orders of magnitude higher input drive power than traditional (60 mW) indicator LEDs whilst retaining the same high efficiency and reliability.
The pioneering work on high-power LEDs began at Lumileds Lighting in 1998 with the introduction of the first commercial high power LED. At 1-W input power, Luxeon devices operate at power levels 20 times that of traditional 5-mm indicator LEDs with efficiencies that can be as much as 50% greater. Commercialization of high-power LEDs in 1998 has impacted the decades-old Haitz’s Law (Fig. 1), manifesting as a knee in the lm/LED versus time plot, defining the point in LED evolution when power LEDs diverged from indicator LEDs. Then came the brightest LED with output 150lm/LED, working with 5W input power.