Sunday, November 9, 2008

Most effcient lights in the world?

Here I am trying to figure out what is the most efficient type of LED light given the lm/w, lm/$ and lm/sqcm criteria that I described in an earlier post to this blog.

The table below has a selection of LEDs that are easy to obtain from online vendors. The luminosity data is that supplied by the manufacturers and I have no way of verifying it as I do not have a light meter yet. I included a 4ft fluorescent tube that works with 220 - 240V ac for comparison otherwise I would only like to focus on lighting that can be powered by DC battery charged by renewable energy sources like PV (solar) panels, wind, pedal powered generators etc.

Please scroll further down the page to see the table

LEDlumens lmpower Warea sqcmcostlm/Wlm/$lm/sqcm
9X1W array3509.0014.44 $15.00 38.8923.3324.24
CREE XR-E on star base1101.302.84 $6.00 84.6218.3338.80
CREE XR-E on star base2283.502.84 $6.00 65.1438.0080.42
high power chip on base601.000.38 $2.75 60.0021.82155.91
lamp type480.070.18 $0.20 727.27240.00265.26
240VAC 4ft flourescent250036.00304.20 $2.00 69.441250.008.22

If we are to believe the data supplied by manufacturers then one can easily see that the 4.8mm wide angle (120deg) LEDs are easily the most efficient lights here in terms of lumens per watt. They also have the advantage of not generating so much heat compared to the CREE LEDs for example. They also knock the socks off anything else in terms of lm/$ and lm/$. I am waiting for some of these LEDs to arrive so I cam construct an LED array of 105 of them on a 63mm X 100mm (2.5" X 4") stripboard (prototype board). I have already built such arrays but with cheap and nasty LEDs of dubious origin. The arrays are driven by constant current circuits. I will show you how to make both the arrays and drivers though the drivers can be bought online for a few dollars but it is more fun and practical to make your own if ordering from the web is a difficult due to lack of payment options (a big problem especially where these lights are most needed).

Monday, October 20, 2008

LEDs: notes on efficiency

Light emitting diodes (LEDs) are solid state lighting (SSL) devices and come in a variety of shapes, sizes and cost. The choice of what type to use for a particular application is dependent on many factors but the one that most people pay most attention to is the efficiency usually given in light output per unit energy supplied to the device. For LEDs the efficiency is usually rated in lumen per watt (lm/W) where the lumen (lm) is the unit of "luminous flux" or the energy within the range of frequencies we are able to see as light. A wax candle outputs about 15lm while a 100W 240Vac incandescent bulb outputs about 1,300. The lumen is defined in terms of candela steradians. What is a candela or a steradian? The candela is the intensity of light. For those who want to get deep the SI definition of the candela is "one candela (cd) is the monochromatic radiation of 540THz with a radiant intensity of 1/683 watt per steradian in the same direction". For Joe Bloggs, a wax candle generates about one candela. The steradian (sr) is another SI unit and is the unit of solid angular measurement. Since the surface area of a sphere is 4*Pi*r*r there are 4*pi or 12.566 steradians in it.

Most LEDs will normally be rated in millicandela (mcd) and some (usually high power ones) in lumens. If we are going to use LEDs for general lighting we should have the light output in lumens (all round) rather than candela (per narrow beam). To convert cd to lm use the following formula

lm=cd*2*pi*(1-cosX/2). where X is the beam angle

The power supplied to the LED can easily worked out by measuring the current, I (Amps)
and the voltage, V (volts) supplied to the LED. It is recommended that LEDs are driven with 20mA of current for the varying forward voltages (depends on colour emitted by the LED). Power, Watts = V*I. Luminous data is usually supplied by the manufacturers but there are independent bodies that carry out tests to verify manufacturers claims. One such independent testing agency is the US Department of Energy (DoE) in their Commercially Available LED Product Evaluation and Reporting (CALiPER) Program, formerly called the Commercial Product Testing Program, that supports testing of a wide, representative array of SSL products available for general illumination. The Department allows its test results to be distributed in the public interest for noncommercial, educational purposes only. Get info here

As I mentioned earlier, the lm/W data is what most people will look at when considering lighting solutions. I feel that this figure does not provide me with all the data I need when deciding what type of LED to use so I have begun to use lm/$ as another yardstick when considering LEDs. Additionally, I also apply a third ratio and that is the lm/sqcm especially when dealing with limited space. I use all three of these efficiency markers when comparing all types of LED against each other. I have not got much data (only 8 LEDs) yet to put up here but one can look at these sites that offer some efficiency data and lots more interesting LED reading:

Tuesday, October 14, 2008

Poverty reduction by bloggng

If a child in a poor nation gets infected with some disease but the parents, friends and neighbours are all convinced that the child is sick because he/she climbed a mango tree belonging to the local traditional healer/spirit medium. If the disease is so serious that the poor child dies do we say that the child died because of the disease or because of lack of correct information?

If one of the ways of defining poverty is a lack of resources then the high infant mortality rates that reduce the number of human resources is an indicator of poverty. The same can be said of literacy/numeracy levels within a population. Uneducated populations are generally poor - to a greater extent than poor populations being uneducated.

With correct information at hand one can make choices that improves lives. Isn't it widely agreed that education lifts us out of poverty? Well, that's information alleviating poverty. Though I must add that some information indirectly leads to poverty - books with titles like "How to make a bomb with grocery store ingredients" are not what I am talking about.

So what am I saying here? INFORMATION, INFORMATION, INFORMATION freely flowing throughout the globe, universal access to this information etc. These are the things that fight poverty by working on the causes and effects. EDUCATION, EDUCATION, EDUCATION. Made freely available to all will fight poverty from the root causes.

Look at the image in this blogs header. See how dark Africa is? Well, there dosen't seem to be enough power to light it up for the kids to do homework at night, or for researches to power up IT. It was enough for me to quit massspectrometry to assemble and install low power computers.

EXCHANGE INFORMATION (blogging for instance) to REDUCE POVERTY. That simple!



Monday, October 13, 2008

My Own Way: LED arrays to replace halogen floodlights

In this blog I will share with you the "why?" and "how?" that LED (forgive the pun) to the creation of what you see here on the left.

Stay connected.

Monday, September 22, 2008

I DIDN"T KNOW: frosted butts, daylight savings time 2008

Digg 1: ourwwworld pilot game: week 2 update
Digg 2: Einstein's Fridge Could Be Cool Idea

I DIDN'T KNOW how the time flew and that the autumnal equinox was upon us again. Our northern brethren are gearing themselves up to adjust to daylight savings time 2008 and in a few weeks time will be tackling the problems of frosted butts and whatever else mother nature chooses to drop on those not near the equator.

Whilst heating may use up a lot of energy in the colder months up north, "middle earth" spends a huge amount of energy keeping cool. This is where
Einstein's Fridge Could Be Cool Idea. There are many off-shoots to this truly elegant idea and one of the best I have come across is the Ammonia Absorption Icemaker. Again, there are numerous takes on this novel solution to solar-powered cooling. How cool! :-)

Monday, September 15, 2008

TALK TO ME: saturday night live, bob levy danny bonaduce fight, no hitter

Digg 1. Breaking News: NY Vote to Ban Texting While Driving

Digg 2.
Talk2me: liverpool vs manchester united,

Will someone talk to me about the hype associated with saturday night live
boxing? I am almost convinced that like wrestling the whole thing is fake. OK some fighters get seriously injured and even die (bad script) but then there are those no hitters who should not get their mitts on the loot after pussy-footing around the ring only to then throw themselves on the canvas and get counted out.

So what happened to the
bob levy danny bonaduce fight "grudge fight"? Two rounds after all the hype. Come on fellas, I know it is rough in the ring but the fight was over before the hot-dog vendors had broken even. Next time stretch it a bit longer so every can make a buck or two just like you.

MY OWN WAY: the day the earth stood still, another universe, waiting

Digg 1. More Cyclists on the Road Mean Less Accidents

Digg 2. Common thread: Oxymoron - Bush Doctrine Wiki, Cheap Gas

My own way of looking at things has led me to think, if it actually happened, the day the earth stood still in another universe time must have done the exact opposite. Moved at infinite speed!

So what was mankind doing or waiting for when the earth stood still and another universe was getting annihilated? Well, some accounts of this auspicious event actually say that there was a fight going on! What would you do if you had the power to make the earth stand still? If scrapping is on your list then we still have a long way to go. Why not turn the music up and chill out knowing that your solar panel is positively relishing the event and the extra sunshine will mean more carbon dioxide is mopped u by the trees and plants on earth. Fighting?? How ancient. But then again, you might go down in history as a great person if you can stop time just to kill a few people.