# Efficiency

Interesting factoids about [replacing sodium vapor lamps with
LEDs](http://dansdata.blogsome.com/2008/12/27/led-street-lighting-not-as-good-as-you-think/)
for city-wide lighting.

- The theoretical lumen/Watt figures for LEDs are worse than
  low-pressure sodium vapor lamps (100 lm/W versus 200 lm/W)
- White LEDs are actually blue LEDs with a consumable phosphor layer
  that turns opaque after a few years of operation.
- Combined RGB LEDs will have better efficiency than a "white" LED.

Other real-world tests have concluded that LED street lights have about
the same lumen/Watt in practice as the sodium vapor lamps ([64 lm/W
LEDs](http://www.olino.org/us/articles/2008/11/02/streetlamp-lioris-aduro-52)
versus [67 lm/W Sodium
vapor](http://www.olino.org/us/articles/2008/12/29/indal-industria-aurora-streetlamp)).

Neon and florescent efficiency [depends on the color and
shape](http://www.signindustry.com/neon/articles/2003-07-11-RC-NeonandFlour.php3):

> \[...\] the fluorescent tube produces between 50 and 100 lumens of
> light per watt depending upon design. Compare this with the typical
> incandescent light bulb that produces between 10 and 20 lumens per
> watt. Neon light efficiency is based upon much fancier pants, the
> color of its output, which ranges from 10 lumens per watt for red to
> 60 lumens per watt for green or blue. One reason that green and blue
> tubes are more efficient is that phosphor coatings used to produce
> such colors better ballyhoo the high-energy ultraviolet light from the
> argon/mercury mix into visible colors. One reason that the fluorescent
> tube is more efficient than a neon tube is that a large straight tube
> offers less resistance to electrical current flow than a skinny bent
> one.

# Obstacles

Little Rock, AK wanted to replace their inefficient shielded lights with
more efficient fixtures, but their contract with Entergy is not a simple
\$/kW formula: [the energy company sets the price based on the type of
fixture](http://www.arktimes.com/Articles/ArticleViewer.aspx?ArticleID=fce07cab-0dea-4fc5-b57e-f1145715f01e).

> \[...\] According to Henry, the city tested out more efficient
> 100???watt HPS bulbs in one Little Rock neighborhood about five years
> ago. When the city asked Entergy to set a rate for those fixtures, it
> was almost double the rate for the 150-watt HPS type.
>
> When asked if Entergy was keeping Little Rock from being more energy
> efficient, Henry said simply, "Yes."
>
> "But how do you fight Entergy?" Henry asked. "I mean, we've had people
> come in and show us new, more efficient lights and we've said, well,
> the problem is, it's not going to save us anything. It will be a whole
> lot less wattage and it will put light out on the street but we can't
> get any benefit out of it because of the tariffs."

# Commercial LED lamps

[SparkFun](http://sparkfun.com) sells LED lamps that are screw
compatible with US light sockets:

- [75
  W](http://www.sparkfun.com/commerce/product_info.php?products_id=8716)
- [12
  W](http://www.sparkfun.com/commerce/product_info.php?products_id=8714)
- [3
  W](http://www.sparkfun.com/commerce/product_info.php?products_id=8717)
- [1
  W](http://www.sparkfun.com/commerce/product_info.php?products_id=8715)

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