LED Craze

[martinmcnally]

You right that you do loose some power in the AC DC conversion process of course. Every electrical component is going to draw power. However you talk about using a direct DC source. The only direct DC source available without AC DC conversion is a battery! If you dont have AC LEDs and you dont want to use batteries your only other option is an AC DC converter.

The 30% inefficiency is way off.

Mean Wells use 12% of their power consumption to generate DC (ELN-60-48D or P version) and Inventronics are slightly better using only 7% (75W version).

[mike31154]

Originally Posted by StirCrazy

Sam, would the chandelier one be good for a dining room with a 5 light chandelier? ya I was hoping the sale would extend to dec also... I bought 10 of the LEDs alread and I need 10 more


Steve

At Costco in Kelowna yesterday they had some 4 watt chandelier type LED lamps in 3 packs. I think they were actually Cree too. $19.99 IIRC. Don't youse have a Costco in Kamloops? Must make it a point to check out that location next time I'm up there.

[mike31154]

With respect to running LEDs on AC or DC. Note that the article I linked to in an earlier post says that LEDs are 'usually' considered to be DC devices. LEDs are nothing more than diodes which happen to emit light. Diodes are commonly used in any number of circuits whether AC or DC. They will conduct when voltage goes positive & block current when it goes negative. They're used in a bridge circuit configuration in most power supplies to rectify an AC signal to DC. A bridge circuit consists of 4 diodes. By hooking them together in this manner the result is a DC output with some 'ripple', so not entirely pure DC voltage. The ripple or noise is minimized by further filtering of the signal using resistors, coils & capacitors.

Therefore, you can in theory run almost any LED on an AC signal, it does not necessarily have to be specifically designed for AC. However, the same way you need to limit the voltage & current when using a DC supply or driver, you need to ensure any AC signal used does not exceed the diode's or LED's maximum current, or it won't live very long. The diode must also be able to handle the reverse voltage while blocking the signal when it goes negative. Depending on the frequency of the AC signal (60Hz in the case of our homes), you will not even perceive that the LED is actually turning off & on 60 times a second. The average human eye can not perceive a flicker at that frequency. That's one of the reasons 60 Hz is used to supply our homes with power. Should that number ever drop into the 40 Hz or lower range, you will start to see a flicker in most lighting, including incandescent & some flourescents.

There are plenty of applications where AC, or for better efficiency, PWM (pulse width modulated) signals are used to drive LEDs. This can save power, reduce heat & increase the life of LEDs driven that way since the power to the LED is actually switched on and off at a high frequency. The main difference between AC & PWM is that the AC is a nice curved sine wave going from positive to negative through a zero reference, whereas a PWM signal is more analogous to a square wave going form zero to whatever the nominal positive voltage is, then back to zero. Our house AC goes from zero to 120, back through zero to -120 and so on. Clearly 120 volts either way would quickly fry any LED in short order. This is why we use some sort of transformer/rectifier or driver to bring that voltage/current down for most LED applications.

Using an AC or PWM signal to power our tank LEDs makes little sense, since we want our livestock, mainly coral to get maximum exposure to the light source and switching to LEDs from MH or T5 is already saving us a bundle in power. We don't want or need to turn the LEDs ON/OFF in rapid succession for our purpose. It does however make sense in small battery powered devices such as headlamps or flashlights, where we want to maximize battery life. Using a PWM in such a device turns the LED off & on rapidly, inperceptible to the eye, but saving power since the LED is turned off for half the time.

Here's an interesting tidbit on the concept. A couple of years ago during a backcountry ski trip, one our ski companions came back inside after dark saying he perceived some sort of strobe effect while watching the snow fall with his Black Diamond LED headlamp. Needless to say we ridiculed him, getting old, too much alcohol, you get the idea. Bruce insisted that he was sober & after some coaxing got a few of us to go out & verify that he was not going bonkers. Sure enough, there was the strobe effect! Back inside we went & started wondering whether we were all seeing things. After some discussion, more beer, wine, single malt scotch, we finally came to the conclusion that BD is using some sort of oscillator circuit (or micro inverter) in the headlamp to turn the LEDs on & off rapidly. Too rapid for the eye to see normally, but the falling snow somehow enabled us to percieve the flicker or strobe, sort of like a helicopter blade when filmed. Personally I found it difficult to believe BD would go to those lengths to extend battery life in something like a headlamp. But it is a competitive market and out in the boonies, where a headlamp could get you back home, you want to get the most out of those 3 AAA batteries. Bruce actually contacted BD after his return & they confirmed that there was indeed a PWM circuit in the headlamp.

Ha, what a saga. If you read all of that, thanks, it certainly took a while to put down.

[StirCrazy]

Originally Posted by mike31154

At Costco in Kelowna yesterday they had some 4 watt chandelier type LED lamps in 3 packs. I think they were actually Cree too. $19.99 IIRC. Don't youse have a Costco in Kamloops? Must make it a point to check out that location next time I'm up there.

ya I have been looking at thoes, but untill i see them in use they can sit on the shelf as they are cool white and I don't want blue light in my dinning room. the ones that philips makes are warm white.

Steve

[StirCrazy]

Originally Posted by mike31154

Depending on the frequency of the AC signal (60Hz in the case of our homes), you will not even perceive that the LED is actually turning off & on 60 times a second. The average human eye can not perceive a flicker at that frequency. That's one of the reasons 60 Hz is used to supply our homes with power. Should that number ever drop into the 40 Hz or lower range, you will start to see a flicker in most lighting, including incandescent & some flourescents.

actually you will see a horrible flicker with the LEDs, and yes you see the flicker on a florescent, it is a bout a 50/50 toss up between people who it bothers and who it doesn't. I never knew it bothered me until I upgraded all my fluorescent to electronic ballasts now I really notice the 60 Hertz flicker on old fixtures. Digital or electronic florescent ballasts are why people don't see this flicker at all anymore as it raises the Hertz to 20,000 or higher. so old people like me who remember when electronic ballasts were a thing only the rich an famous could afford

in the case of LEDs they show the flicker even more because they only produce light on one of the wave lengths of a cycle (where every other light uses both sides of the wave, so they are already off 1/2 the time on a ac signal, so this intensifies the 60 Hertz flicker.

you will have to be down to about 40 or 30 Hertz before an incandescent will show a noticeable flicker and for them they are not actually turning on and off but rather a slight dimming as the element cools. I have had a 40 watt bulb down to 25 Hertz and while after a bit it would be annoying, it was not really a flicker but rather it would dim and bright dim and bright, but fading between the two extremes not on off

Steve

[Samw]

Originally Posted by StirCrazy

Sam, would the chandelier one be good for a dining room with a 5 light chandelier? ya I was hoping the sale would extend to dec also... I bought 10 of the LEDs alread and I need 10 more


Steve

Hi Steve. I think you will like them. But best buy 1 and see for yourself or see if your nearest HD has demos on the floor.

[mike31154]

Originally Posted by StirCrazy

actually you will see a horrible flicker with the LEDs, and yes you see the flicker on a florescent, it is a bout a 50/50 toss up between people who it bothers and who it doesn't. I never knew it bothered me until I upgraded all my fluorescent to electronic ballasts now I really notice the 60 Hertz flicker on old fixtures. Digital or electronic florescent ballasts are why people don't see this flicker at all anymore as it raises the Hertz to 20,000 or higher. so old people like me who remember when electronic ballasts were a thing only the rich an famous could afford

in the case of LEDs they show the flicker even more because they only produce light on one of the wave lengths of a cycle (where every other light uses both sides of the wave, so they are already off 1/2 the time on a ac signal, so this intensifies the 60 Hertz flicker.

you will have to be down to about 40 or 30 Hertz before an incandescent will show a noticeable flicker and for them they are not actually turning on and off but rather a slight dimming as the element cools. I have had a 40 watt bulb down to 25 Hertz and while after a bit it would be annoying, it was not really a flicker but rather it would dim and bright dim and bright, but fading between the two extremes not on off

Steve

You have sensitive eyes then. I ran the 12 volt DC MR16 4 watt LEDs I got off both a 12 Volt AC wall wort & a 12 Volt DC one which is what they are currently running on. Did not see a flicker with the 12 VAC supply, but there was quite an audible 60 Hz buzz, so decided not to stay with that scenario, since there's no point trying to save power over my kitchen sink. Three MR16 bulbs at 4 watts each are already providing way more light than the 4 old halogen ones without having to run the LEDs on half cycle.

Ha, ha, since you notice the 60 Hz flicker of light fixtures, you'd really be knackered in Europe then, where they deliver the 220 Volt AC line power at only 50 Hz. You'd have a never ending headache from your lights.

[StirCrazy]

Originally Posted by mike31154

Ha, ha, since you notice the 60 Hz flicker of light fixtures, you'd really be knackered in Europe then, where they deliver the 220 Volt AC line power at only 50 Hz. You'd have a never ending headache from your lights.

ya, but in the three years total I have spent in europ, middle east and such, a lot lighting was halogen or incadesent. they also have been using electronic ballasts for there florescent way longer than us, so realy it isn't bad.

lots of peopel are sensitive to the 60 hrtz they just don't realize it. lot of headaches and ect from office enviorments and such.

Steve

[Seth81]

With the dimmable LED drivers they have now boasting 92% efficency, I'm not too sure why anyone would bother going AC. I just finished my DIY CREE XM-L LED fixtures, with some Royal Blues, they are sooo much brighter then I expected! Now to connect them up to my PLC and program a day/night sequence