The discussion about hydrogen cars in the Energy forum (which turned into more of an energy storage discussion) got me thinking about ways to conserve energy. We use LED on a limited basis in our house: 2 replacement "bulbs" in lieu of incandecents, a string of white LED Christmas lights that stay up all year as "night lights", and colored LED's on the Christmas tree and windows. Otherwise we use compact flourescents everywhere else with the exception of two incandecents and one halogen outdoor flood light.

Our two LED bulbs that replace incandecents are made with 36 LED bulbs each, set into a base that screws into a standard socket. They use substantially less power than even the CFs, but their light is very blueish. Sort of like the soft blue light you get at dawn. Our string of night lights have the same blue cast. This is nice as long as it's mixed with the warmer light from the cf's, but by themselves they make a room look really, really cold. It's this quality that keeps me from using more LEDs.

I think that this is also the thing that keeps LEDs from entering more of the mainstream market. That and the current cost for household replacement bulbs. If solutions could be found that would make the light quality better and that would lower the cost for household use, then why couldn't we light up the nation using LEDs?

At SolWest Renewable Energy Fair last year I saw a gentleman demonstrating a floodlight that uses all LED bulbs. It was a super powerful beam: the kind you would use to light up a construction site or to illuminate a flag at the top of a tall pole. While I was watching he turned a knob to change the frequency and the light changed accordingly. He could manipulate the bulbs across the entire visible spectrum and ultimately to a pure, bright white.

I would be interested in using more LEDs if I could get this kind of pure white light. Or even cooler - if I could manipulate them to get colors! (Think "mood" lighting )

Do any of you have experience or knowledge about manipulating the color of LEDs, especially to get white light? Also, does anyone know what the environmental impact is for production of LED bulbs?

Dan

I am pretty farmiliar with LED's, I have used them in commercial products for years. They all have a very narrow color frequency that is based on the solid state material being used in there construction, I don't know of any approach to powering these that would allow the color of any one type of led to be changed more than a tiny amount but the brightness can easily be controlled. The color frequency will shift a very small amount based on the amount of current passed through them but the color will always be in the same color range.

The three basic colors needed to make up white light are red, green, and blue, individual LED's are available in all of these colors so I suspect he actually had all 3 colors of led's in his light assembly and used electronics to very the brightness of the verious colored LED's to create the continuous variable color output. This could be accomplished with any one of several methods using electronics but most likely the current through the 3 different color LED's was pre-programmed to allow a smooth shift across the entire color spectrum.
Using a combination of these three primary colors should produce a pretty pure white light. individual LED's sold as "white" use a bit different approach to produce what our eye perceives as an almost white light.


There are modulation techniques that can be applied to LED's to cheat the eye, one method is to pulse them with a high current at a relatively slow rate (the pulse rate has to be above the persistance rate of the eye, that is about 20 pulses/sec) they will appear brighter than when using a lower current and keeping them on continuously, this technique also uses less current. This technique does produce very distinct strobed pulses of light in reality so you don't want to use it around spinning machinery, the motion of the machinery can appear to be stopped under certain pulse rates, folks have lost body parts by reached into spinning laths and such under florescent lights as they does the same thing.

White LED's -- These don't quite yet exist in reality, it is being developed but not yet available commercially, LED's sold as white are actually a very nerrow color of blue light being emitted from the solid state junction, then the blue light is passed through a yellow filter that is deposited directly over the light emitting solid state junction. This gives two very narrow but distinct color outputs from the device but the eye interprets this as an almost white light.

The physics of the material making the blue light allows a very bright light to be produced with only 20 MA (.02 amps) or less of DC current. Each individual LED will need about 3.5 volts across it to light, by seriesing several leds together you can light them all with the same 20 MA of current, 3 seriesed led's seriesed with one 75 ohm 1/4 watt resister can be powered with 12 volts DC, 6 leds and a 150 ohm resister would work fine powered with 24 volts DC.

I have considered replacing my home lighting with home-built LED light fixtures powered by 12 volt DC batteries, keep the batteries charged from 1110 volt AC power but the batteries take over during power outages. A fairly small 4 X 4 X 6 inch 12 volt 12 amp/hr gell cell battery would light a 60 LED fixture for over 24 hours continuously.

Extremely bright white LED's are available shipped directly from china in bulk quantities of 100, 500, 1000, 10,000 on Ebay for as little as 12 to 21 cents each including shipping (Ebay sale = 500 quan, very bright, T 1 3/4 - 5 MM, 12 cents each with shipping).

Placing 60 of these LED's in one bowl shaped ceiling fixture would draw only .4 amps powered with 12 volts DC or .2 amps powered with 24 volts DC.

This light fixture should be bright enough to allow a yellow, or whatever color, filter to be placed over the entire fixture to shift the color output to whatever is desired and still be adequately bright. By adding a simple PWM (pulse width modulated) dimmer control the brightness could be controlled from full off to full on.

This is great information - thanks for replying!

Do you know of any online schematics or instructions that I could look at to see how to put something like this together? I like your idea of the 60 bulbs in a fixture: I'm thinking of a fixture on the end of a flex tube so it can be moved around and "aimed" however we want it, with a dimmer mounted on the wall.

Would wiring it into my household 110V system blow it, or is that what the resistor does? ("Resist" current to diminish the supply?)

Sorry for such basic questions, but I'm really new to this - as you can tell!

Dan

I did a general web search for "wiring up leds", found MANY web pages about the basic info, look over some of these and then ask me again once you have a bit more of the basics.

the 110 volt AC voltage will have to be converted to DC voltage, easy and cheap, a couple bucks for the parts at most (or free from an old computer, TV, radio/vcr etc), you will end up with about 150 volts DC, each LED needs about 3.5 volts so you can wire something like 40 LED's in series (series is "end-to-end", if one went out they would all go out, luckily led's last around 10,000 hours before going out if the current and voltage is kept in spec) plus one small 10 cent resister to keep the current and voltage in spec.

I had not thought of using a cheap $6.00 AC lamp dimmer but it might sorta work to dim the led voltage, it may not be exactly linear, probably only do any dimming in the last 1/10 of a turn of the knob do to the very tiny .02 amps of current drawn by the 40 led's. these dimmers are designed to dim 100 watt incandecent bulbs, each one of these draws about 1 amp.

Other approaches can be done for just a few bucks.

You won't need 60 led's for the type lamp you describe, 5 or 6 bright led's would probably be enough. I use two flashing super bright red led,s as the alerting device in a power monitering unit, these led's will light up a dim room all by themselves, they are so bright that looking directly into them can not be done.

You might do some testing with a few bright led's, All Electronics is a surplus dealer that has several bright, ultrabright, and even super ultrabright leds for about a dollar or less each.

Brighness -- The XXXX MCD brightness numbers shown on the Ebay sales are highly subjective, mostly advertising hype, you will need to study the manufacturers actual data sheet to get more realistic brightness info but for our lighting purposes this is not too big of a problem. I suspect the brightness of the individual leds in the bulk orders from Ebay will also vary a bit from one to another, these will likely be the led's that fell a bit outside the industrial specs, uniformly bright and in-spec leds will definitaly cost more.

Everything I've read indicates that compact fluorescent lights (CFL) and cold cathode compact fluorescent lights (CCFL) use less energy for the same amount of light as the LED's.

The primary difference is that LEDs usually have a fairly tightly focused spot, and CFLs and CCFLs produced defused light unless coupled with a reflector.

Certainly there are roles for both types of lighting.

The compact florescents that I have tried have been duds, they do last longer than cheap incandescent bulbs but not anywhere near as long as advertised. Standard straight 4 ft tube florescents are fine but the screw-in compacts don't do it for me, they were advertised to last up to 8000 hours but I was going through one about every 6 months, more like 2000 hours, they also don't glow very bright on 12 volts DC.

The florescents also take a bit of getting used to in cold rooms, they start out extremely dim for the first several minutes, not a problem, but a nuisance.

individual leds definitely have a narrow beam angle, but if you put many of them over the outside area of a concave shape and then put this concave shaped led assembly inside a normal frosted glass ceiling fixture the light will be diffused.

If you are making up a movable reading light then the LED's are about perfect if you use several individual leds in an array. There are several of these type led reading lights already on the market.

Power used -- This energystar.gov web page says a 100 watt comparable light puts out 1600 lumins, THIS LED MCD-to-lumens calculator indicates it will take something like 375 of the narrow angled 20000 MCD led's to put out 1600 lumens of light, the power calculated for that many leds comes out to 27 watts, about the same as for a comparable compact florescent - BUT - I am confident that 375 high intensity leds will put out MUCH MUCH more light than the 25 watt compact florescent, these bright leds are really really BRIGHT, and will actually last for 10,000 hours.

I will do some testing on this, I need to order some leds anyway.

just ordered 100 13,000 MCD 20 deg leds on ebay for $6.90 including shipping, not the brightest listed but someplace to start testing.

They also list warn-white 120 deg leds (these) for about the same price, maybe try these next time.

I wonder if people off-grid could use mostly skylights to let sunlight in through the roof by day, and then also use solar pannels to charge batteries which would power LEDs after dark?

quote:

originally posted by Coyo

Our two LED bulbs that replace incandecents are made with 36 LED bulbs each, set into a base that screws into a standard socket. They use substantially less power than even the CFs, but their light is very blueish. Sort of like the soft blue light you get at dawn. Our string of night lights have the same blue cast. This is nice as long as it's mixed with the warmer light from the cf's, but by themselves they make a room look really, really cold. It's this quality that keeps me from using more LEDs.

Yeah I hear ya. As a guy who does use leds for the last 5 or 6 years those blues lights (about 8000K )were a pain and I only used them outdoors. I use 57 diode back up lights for outdoor lighting (3 for a total of 12 watts). This ,mounted high lights up a rather large area

the good news is yes there are warm whites available. the bad news is you have to build your own lights which is not hard to do @ 12volt at all. I just converted my diningroom light yesterday and found this thread this morning,wierd

You can find warm white led's here
I've ordered a 10 piece of those and had no problems getting them and will be ordering more.

those are a lot closer than the blueish ones but seem a little yellow. For the best warm white (that I have found anyway) is this site and they are aboiut perfect,as close to natual light as a 3oooK floureccent. They are also more expensive at about a buck a piece but they last so long as a light source that it's worth it in the long run

I will be buying more of them as well.

As for the "mood lighting"?

you can buy rgb's (red green blue) sets and with the appropiate drivers can have any colour of the spectrum or all if you choose

quote:

Originally posted by welder:
I wonder if people off-grid could use mostly skylights to let sunlight in through the roof by day, and then also use solar pannels to charge batteries which would power LEDs after dark?

the nice part about led's is tho low power consumption so you don't need a lot of panel to cover the wattage. Perfect for camping or other remote areas

Tim

what I found when wiring for 12 volt is to forget the resisters. wire 3 leds in series and parralell the groups of three. You overdrive them a little bit for more brightness and save on the resisters as they seem to be the weak link to burn out. Then the diode fries. They seem to take the higher voltage so far with very few burn outs compared to the ready made units I've bought.

just a thought

and the morning news

LEDs And Smart Lighting Could Save Trillions Of Dollars, Spark Global Innovation

Running on 12V is my goal even though we will always be on grid. I hope to get this place prepped so if we have prolonged outages we can use backup power supplies, and even during full power it would be great to reduce my consumption.

Another option I thought of that I'll have to experiment with is mixing the blueish/white bulbs with a few reds and/or yellows to warm up the cast a little. When I got full-spectrum lights at work I initially objected to the brighter "blueish" light, so I put a few red and yellow crepe paper streams across the fixture and it warmed the room right up. A few colored bulbs might have the same effect.

I'll check out those websites when I have a moment. Right now I need to get going to church.

Dan

quote:

Originally posted by 12voltdan:

what I found when wiring for 12 volt is to forget the resisters. wire 3 leds in series and parralell the groups of three. You overdrive them a little bit for more brightness and save on the resisters as they seem to be the weak link to burn out. Then the diode fries. They seem to take the higher voltage so far with very few burn outs compared to the ready made units I've bought.

Not to mention that resistors are very inefficient.

Essentially if you wire a resistor in series with the LED, then you waste all the energy running through the resistor.

I was wondering if you could wire 3 or 4 LEDs in series and forget the resistors...Thanks for the tip, 12voltdan! I just ordered 100 cheap bright white 5mm LEDs to try out.

I have also ordered a batch of LEDs from eBay. Time to start playing, experimenting, and learning!

Dan

I've got a question for whoever has the answer:

What does the abbreviation " mcd " (in lower case letters) mean?

As in : 2000 mcd LED or
4000 mcd LED

Anyone know?

Is it a brightness rating?

Does it refer to lifespan?

Is it material composition ? (ie polymer density etc)

mcd (millicandela)is a brightness rating of LEDs

Here is an excellent web page about LEDs, and includes some luminosity calculators.

http://www.gizmology.net/LEDs.htm

quote:

The brightness of LEDs is measured in millicandela (mcd), or thousandths of a candela. Indicator LEDs are typically in the 50 mcd range; "ultra-bright" LEDs can reach 15,000 mcd, or higher (the 617 nm Luxeon Star (part number LXHL-NH94) can reach 825,000 mcd).

By way of comparison, a typical 100 watt incandescent bulb puts out around 1700 lumen - if that light is radiated equally in all directions, it will have a brightness of around 135,000 mcd. Focused into a 20° beam, it will have a brightness of around 18,000,000 mcd.

Note,
Typically LEDs have a focal angle. So, while incandescent, and CFL lights often have over a 180 degree focal angle, LED's often have much tighter angles such as 20 degree focal angles, or even less. And, thus a light that could project a bright spot on the wall at 10 degrees or 20 degrees might not be very bright if illuminating a room with a 180 degree focal angle.

The same is true with incandescent lights, and you can get very strong beams by adding reflectors.

quote:

mcd (millicandela)is a brightness rating of LEDs

Here is an excellent web page about LEDs, and includes some luminosity calculators.

http://www.gizmology.net/LEDs.htm

Thanx Keelec.

Good info...

I was rummaging around the All Electronics site that Tim Cook linked to and found some pretty neat stuff.

For example:

http://www.allelectronics.com/make-a-store/item/MK-8071...ED-LED-DRIVER/1.html

I couldn't help wondering if something like this would be useful in really putting out some significant light. It only takes 4 KEDs max, but it's supposed to take really strong ones...

quote:

http://www.allelectronics.com/make-a-store/item/MK-8071...ED-LED-DRIVER/1.html

I couldn't help wondering if something like this would be useful in really putting out some significant light. It only takes 4 KEDs max, but it's supposed to take really strong ones...

Odd little device.
Input voltage: 6-12VAC/9-18VDC.

The page I had linked to earlier had an interesting discussion about resistors and LEDs. And the suggestion of using a voltage regulator or a current regulator.

I suppose the problem with batteries is the variability in voltage.
14V (or slightly higher) - Max charging voltage.
12.5-13V - Fully charged.
10.5-11V - Discharged Voltage.

It doesn't sound like the LEDs can stand such variability.

This message has been edited. Last edited by: keelec,

I'm having no problems with mine. The ready made ones with resitors have a couple out. My oldest is about 6 or seven years old now (with extensive use)now and I'm missing three out of the 57 in the unit

way more reliable that the florescents

I haven't lost any of my own make yet with some over a year old now