LED help

[Scootie]

I have looked into those because you can get ones that produce UV light and I have some UV reactive fans and cable covers already in the case.

[YT2095]

cold cathode lights.

 

THAT`S the name I was looking for

[Thomas Kirby]

A lot of electricity can be saved using LED lights. Most situations where you need a little bit of light, one or just a few white LEDs can illuminate that area bright enough to read using a fraction of a watt. Trying to read with an LED headlamp doesn't work so well for me because it's too bright. I would actually have to turn it down or place the illuminator farther from the book.

 

White LEDs are also good for illuminating dark corridors, for night lights, and outside area illumination. It isn't quite as bright as incandescent, but the illumimation seems very clear. One thing that's great is that even when dimmed the LEDs don't appear to change their spectrum. The 60 watt bulb in the ceiling is too red to read resistors by. I use the headlamp.

 

It would be quite easy to power all the illumination you need in a house, cabin, or camper from a small solar panel this way.

 

They do last for a very long time, at least 7 years continuous by the ratings and they fade instead of burning out. They are really good for emergency lighting. An emergency light can last for weeks on any decent sized battery.

[YT2095]

well lets see, 240v at what??? say 50ma max, sound about good?

 

1 Amp / 50ma = 20 (so 20 hours to draw a full Amp)

 

20 X 1000 = 20,000

 

that`s the amount of hours to use a kilowatt, and that will cost you about 6 pence in UK money.

 

yeah, looks like a saving and a half! ))

[Thomas Kirby]

That's about 2.4 kilowatthours per 20 hours using your values, YT2095. (my mistake, .24 kwh in 20 hours) Try five rooms, three illuminators each, standardized at 12 volts * 50 mA per illuminator. That's .6 watts each times 15 for 9 watts. About 111 hours per kilowatthour. If your power capacity is really low you can turn off the unused ones and run the ones you have to have at much lower currents. If I weren't so lazy I would have fitted the entire place with them by now. The one I've built is bright enough to read by easily using 9 volts at 4.5 mA. At about 50 mA (six LEDs, sets of three wired in series, two sets parallel to each other), it's bright enough to use as a flashlight at a decent distance, able to make street signs readable at over a hundred meters.

 

It's low tech at my end, just find something to fasten them to and wire them up to a 12 volt power source. A 12 volt 750 mA output transformer can do the whole house.

 

You aren't getting the same illumination, but you are getting usable and practical illumination for a hundred or more times less power. Compare it to five 60 watt bulbs, which if run 24/7 would use 21.6 kwh per month. That's not very much money a month around here, no, but energy seems to be becoming increasingly expensive lately. Then you realize that the fixtures can be less expensive, less demanding of wiring, will last much longer, provide excellent solutions for dark hallways, and so on, plus leaving them on doesn't even move the meter. Realize also that some people leave three hundred or much more watts on continuously just to illuminate dark areas that they almost never use.

[newty]

A quick question here... But, first a little background: I am planning on using LEDS to make a moonlight system for my saltwater tank (I have LEDS that produce output in the correct wavelength). I am planning on putting these LEDS inside a hollow acrylic tube to waterproof the connections. The inside diameter of these tubes are short. I am wondering if I could cut off the long extending wires from the LEDS (I cannot for the life of me think of the proper term) so that it would be shorter and I could easily orientate them in the acrylic tube. Is it ok to do this?

 

Newty

[YT2095]

only if you`re VERY GOOD and FAST at soldering, they don`t like much heat to get into them with the epoxy shell, have you got a pair of Heatsink Clamps you can use?

[Thomas Kirby]

Yes it is. Try to keep soldering heat at least an eighth of an inch (3 millimeters) from the case. They are called the leads. The "ea" sounds like the "ee" in "reeds".

[newty]

only if you`re VERY GOOD and FAST at soldering, they don`t like much heat to get into them with the epoxy shell, have you got a pair of Heatsink Clamps you can use?

 

Heatsink clamp: nope. Just have a soldering gun and some wire. I guess I will have to leave at least 3 mm as mentioned below. Probably will leave around 5 mm or something like that.

 

Thanks, Newty

[Lance]

I don't think people would LED's in a computer case because they are trying to save power.

[Lance]

Heatsink clamp: nope. Just have a soldering gun and some wire. I guess I will have to leave at least 3 mm as mentioned below. Probably will leave around 5 mm or something like that.

 

Eek! I would NOT try to solder LED's with a soldering gun. That is asking for trouble. You should go buy yourself a decent iron (NOT a plumber's iron) first.

[newty]

Maybe I didnt mean a gun-style. What i meant that the handle is like a screwdriver and the metal unit slowly tapers toward the end and the end is a very fine point. I have used it before and it worked for other small appications. I don't know the terminology, unfortunately. I only know techie words for molecular sciences!

 

Newty

[Lance]

Maybe I didnt mean a gun-style. What i meant that the handle is like a screwdriver and the metal unit slowly tapers toward the end and the end is a very fine point. I have used it before and it worked for other small appications. I don't know the terminology' date=' unfortunately. I only know techie words for molecular sciences!

 

Newty[/quote']

 

Ah, okay. Thats a normal soldering iron. A soldering gun is shaped like a gun and has a V-shaped wire for it's tip.

[Thomas Kirby]

There is a safety issue that I have to mention. A straight line of LEDs across any line that can supply a few hundred milliamps or more is potentially dangerous in an unpredictable way. Basically, it is potentially dangerous if it carries enough current to set one unprotected LED on fire. The upward curve, current vs. applied voltage, is too steep. An LED can burn and form a short circuit, its voltage drop can change just enough, or several in the string, the applied voltage can increase just enough to cause a runaway condition, and temperature can affect the voltages. The reverse voltages are not predictable if you string a bunch of them across the mains or any source of AC current, and that's another source of problems.

 

One resistor and one diode eliminate almost all of the potential fire hazard. One resistor of the right resistance and power rating makes it so that you know how high your current will ever go, and resistors aren't nearly so prone to thermal runaways or burning shorts. One diode prevents any reverse currents from flowing. Your lighting project is then safer and will last much longer. You also don't have to worry about attempting to precisely match the voltage drop of your string of LEDs to the supply voltage. One of my illuminators would work just as well from 48 volts as from 9 and no worries about burning out or starting fires.

[newty]

I apologize for hijacking this thread, but I have another question: is it possible to dim LEDS in tandem? By anology, I would like to stimulate a dusk-dawn effect.

 

Newty

[Lance]

Do you want it to be in-sync with the real sun rise/set?

[YT2095]

I apologize for hijacking this thread' date=' but I have another question: is it possible to dim LEDS in tandem? By anology, I would like to stimulate a dusk-dawn effect.

 

Newty[/quote']

 

certainly, all you`ll need will be a transistor, 2 resistors and a photocell, depending on where you bias the photocell you can either get it to dim or go brighter according to ambient lighting

[newty]

Do you want it to be in-sync with the real sun rise/set?

 

My thinking is that the LEDS are turned on when only my actinic lights are on, and that the LEDS progressively get brighter and would be at full strength by the time the actinics turn off (1.5 hours) and vice versa for the dawn effect.

 

Would the abovementioned equipment be sufficient for that task? My only experience with these LEDS is soldering the resistors and LEDS in parallel and wiring it to a normal wall adaptor.

 

Newty

[Thomas Kirby]

How precise do you want these to be? Without some fairly sophisticated stuff, your setup might be able to pinpoint the first light outside, but it's going to be a lot harder for it to anticipate the last bit of twilight. At best, one sensor is going to have to be set for the transition from darkness to dawn, and another sensor is going to have to be set to detect sunset. Each is going to have to trigger a timer that progressively dims or brightens the LEDs over an arbitrary period of time. An hour and a half can be done using some kind of RC circuit, but it will be temperamental and not particularly stable.

 

This gets to the point that it could be easier to use a microcontroller board with a real time clock and analog outputs. A Basic Stamp can be had for less than 50 US dollars, and there are some others around. The Stamp can be programmed from your PC. It could well be easier to write a program that includes a way to calculate times of sunset and sunrise than to try to get sensors to do it accurately.

[YT2095]

TK, WHY do you have to OVER COMPLICATE things? this device is INSTANTLY reactive, what the problem here?

[Thomas Kirby]

Newty asked for the lights to dim or brighten over a period of 1.5 hours after being activated. I'm not sure I can completely make sense of what he said, either. If the circuit has to detect the first light of dawn for one phase, then detect the sunset for the other, we have complications. It's easy to reliably detect the first light of day, and much harder to detect the moment the sun sets, depending on the weather. This gets complicated and less reliable.

[reverse]

..... just so i can walk away having learned something... would i be correct in saying "LED's are not like a light bulb or any other load on a circuit in that they have no resistance" that is why a resistor (or current regulator) is needed to keep the current under control.

 

Highschool physics is the extent of my electronic knowledge but im looking to learn more.

 

LED’s are way cool.

I’m a bit rusty but I think this is how it goes…

 

Yea..

sometimes when you put them in series…one can glow brighter than the other…unless they are made at exactly the same time by the same manufacturer.

 

You can put only a small amount of electricity into an led and it will glow only slightly…or if you put more electricity in.. it will glow much more intensely.

 

You can overdo it…and then you will kill it.

 

Basically use the V= I x R equation to figure out what you need.

 

V = volts

I = current …usually measured in milliamps…(that’s amps divided by a thousand…. because a whole amp is waaay too much to use).

R = resistance usually measured in Ohms.

 

Now remember this equation was made up ages before LEDS even existed ..so they might use the word resistance to describe a similar property of LED’s but not exactly the same property as the actual resistive wire used at the start of electronics.

 

Get your twelve volt output on your computer power supply

 

So V = 12

 

And read the specs on the led to see how much current you need.

It might say 120mA… (times that by 1000 to get Amps).

 

So V = I x R

Divide both sides by I

 

So V/I = R

 

So 12V divided by 0.120A equals the resistor you need.

[Pleiades]

It might say 120mA… (times that by 1000 to get Amps).

You mean divide 120mA by 1000 to get amps.

 

Moving on: If the voltage drop of diode is greater than or equal to the supply voltage, do you still need a resistor (assuming you use a battery for the power supply)?

 

Also, let’s say you use a 2.5v LED @ 30mA and the appropriate resistor in series with a 9v power supply, how much power is lost to the resistor? According to http://led.linear1.org/1led.wiz you need a 220ohm resistor that burns 500mW while the LED only burns 75mW. If you are concerned about saving power, you should always try and match the supply voltage and the LED forward voltage.