# Are residential LED lightbulbs in our future?

**URL:** <https://boards.straightdope.com/t/are-residential-led-lightbulbs-in-our-future/213511>\
**Category:** Factual Questions\
**Created:** [November 16, 2003, 4:15am UTC](https://boards.straightdope.com/t/are-residential-led-lightbulbs-in-our-future/213511 "2003-11-16T04:15:20Z")\
**Posts on this page:** 3\
**Page:** 2

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**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\
**Post date:** [November 17, 2003, 1:04am UTC](https://boards.straightdope.com/t/are-residential-led-lightbulbs-in-our-future/213511/21 "2003-11-17T01:04:29Z")

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> \*Originally posted by Chronos \*  
> **If colored LEDs are more efficient than the phosphor white ones, then why not use the RGB (or other color mixing) scheme to produce white LED light? A mixture of colored LEDs can’t be any less efficient overall than the least efficient color.**

I think the statements about coloured LEDs being more efficient were in comparison to a non-LED white light source covered by a coloured filter - so it is more efficient to use red LEDs for vehicle brake lights because they only produce light in the desired band, whereas conventional lights produce a broader spectrum, most of which is thrown away as it passes through (actually _doesn’t pass through_) the red plastic lens.

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**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\
**Post date:** [November 17, 2003, 1:20am UTC](https://boards.straightdope.com/t/are-residential-led-lightbulbs-in-our-future/213511/22 "2003-11-17T01:20:24Z")

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> [@](#):
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> \*Originally posted by Mangetout \*  
> **I think the statements about coloured LEDs being more efficient were in comparison to a non-LED white light source covered by a coloured filter…**

No, I’ve been thinking about this, and it makes sense that white LEDs which use a UV emitter to energize phosphors would be more efficient than normal LEDs which do not need or use phosphors. There is some loss, since not all the UV radiation is converted to visible light by the phosphors.

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**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\
**Post date:** [November 17, 2003, 1:48am UTC](https://boards.straightdope.com/t/are-residential-led-lightbulbs-in-our-future/213511/23 "2003-11-17T01:48:29Z")

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> [@](#):
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> \*Originally posted by Chronos \*  
> \*\*As for running an LED straight off the mains (or with nothing but a resistor in between), that’s going to be awfully ineffecient, and probably not too good for the LED, either. Remember, the D stands for diode, and house current is AC. Voltage across an LED in the wrong direction won’t light it up, and might damage it. \*\*

**Chronos** : Chip designers have come up with efficient and reliable methods to drive LED arrays from 120 VAC. The [Supertex HV9906](http://www.supertex.com/feature_hv9906.html) is one such example. It can drive hundreds of LEDs from 120 VAC, and doesn’t even require a transformer. It employs a nifty switching scheme that precisely controls current from the power mains. The data sheet is [here](http://www.supertex.com/pdf/datasheets/HV9906.pdf).

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