It’s hard to compete with the luminous output of a ball of hydrogen and helium gas 864300 miles in diameter, but it should be noted that sunlight is not without its drawbacks.  It’s nearly impossible to use at night, and the quality of light is affected by everything from cloud cover to latitude.  Fire works indoors and at night for light, but it’s not very bright, often rather smoky, and could potentially rage out of control and destroy one’s house.  Incandescent light bulbs use too much electricity and put out a kind of yellow or light that doesn’t render color the way sunlight can.  They also burn out with irritating rapidity.  And don’t get me started on fluorescents or sodium halide.

Image courtesy http://coolcosmos.ipac.caltech.edu

The solution these days is to use LED bulbs.  They’re adorably tiny, use very little electricity, and they last for ages.  The problem has been that individual LED’s don’t put out enough light to compete with standard light bulbs for everyday interior/exterior use by people living in homes and working in offices.  Researchers from the Nichia Corporation in Tokushima, Japan have developed a white LED that with “a luminous flux of 1913 lumens and a luminous efficacy of 135 lumens per watt at 1 amp – [can] emit more light than a typical 20-watt fluorescent bulb, as well as more light for a given amount of power. With these improvements, the researchers say that the new LED can replace traditional fluorescent bulbs for all general lighting applications, and also be used for automobile headlights and LCD backlighting” (Zyga). 

Image courtesy crunchgear.com

The researchers focused on how luminous the lights appeared as perceived by the human eye (luminous flux), as well as how luminous they were given a certain amount of power (luminous efficacy).  They fabricated three types of white LEDs, “each of which utilized a variety of improvements in device structure to improve their luminosity, or brightness, and reduce their operating voltage” (Zyga).  All of the white LEDs were based on blue LED dies, each coated with a yellow phosphor to widen the emission spectrum.  The blue light emitted from the LED die mixes with the yellow fluorescence from the phosphor to produce white light.  Red phosphor was also added to balance the spectra (Zyga).  The resulting LEDs produce whiter light at lower voltage than ever before.

“The cross-sectional structure of (a) a conventional LED and (b) a new high efficacy LED with the patterned sapphire substrate and ITO contact as p-type electrode, which reduce the optical absorption and improve the extraction efficiency. Credit: Yuko Narukawa, et al.” Via: Physorg.com

The design improvements point to a world where solid-state lighting replaces our everyday light bulbs.  Although the new white LEDs are more expensive than others on the market today (natch) the price can only come down as economies of scale kick in.

WU XING:

I’m filing white LEDs under FIRE, similar to another post I wrote about LEDs that emit green light (which I hope you’ll check out at your leisure).

Cited:

Zyga, Lisa. “White LEDs with Super-high Luminous Efficacy Could Satisfy All General Lighting Needs.” Physorg.com 08/31/10.  Accessed 09/02/10.  URL.

More:

Yukio Narukawa, et al. “White light emitting diodes with super-high luminous efficacy.”J. Phys. D: Appl. Phys. 43 (2010) 354002 (6pp). DOI:10.1088/0022-3727/43/35/354002