ECN Forum Forums General Topics of the Trade General Discussion Area LED bulbs

I thank each and everyone for the replies. I was just wondering if the LED lights were as good as "they" say they are. I was thinking that a LED light might not be damaged by high voltage problems like the regular incandescent bulb. I have the POCO transformer right outside my house, so the normal voltage here is between 125-130 volt. The normal 120 volt bulb doesn't last long at all. I went to the compact florescent bulbs and they last a lot longer. They are not able to be dimmed either, so I thought that may there is a LED type of bulb that could fill my need.

Harold are you sure you don't have dimmable CFL's available?

Up here in Canada they are on the store shelves at the big box stores. I think that Globe is one of the brands that makes them.

I don't have any but one of my friends put some in his basement rec room and was not impressed with the bulb life and he was not running them dimmed that often.

IMO,
Any attempts at trying to dim either a CFL or an LED lamp, would be pretty much fruit-less.

Reason I say that is because, look at the way that this technology works.

A Compact fluorescent lamp is just a smaller version of a 3-4-5-6ft linear tube.
If you reduce the voltage through that tube, the arc that keeps the lamp lit will fail, hence darkness.

On the same side of the coin, an LED is purely a P-N junction that requires a certain "bias" voltage to keep it lit, go under that, you get the same result as above.

The only way you are going to achieve actual "dimming", is to turn off individual LED's or parts of a CFL.
With current lamp-holder technology, that won't be happening any time soon.

Googled dimmable CFL and LED and found both are available. They have drawbacks though, like flicker and startup time.

LEDs might have early end of life problems but they should dim OK and there is no warm up time. The thing that burns your recordable CDs and DVDs is a LED and it goes from off to full on in a fraction of a microsecond.

Greg
I was thinking the thing that burns DVDs and CDs is a RLD.
(red laser diode). Are you sure an LED can also do that kind of work?
Just curious.

That is still a type of LED. The silicon junction emits light as soon as it is energized. There is no warm up time like you have in a filament or the slower CFL.
You also see the light output vary, based on the current going through the junction. It is probably not as linear as a filament but it is purer in color. ... at least that is what I see when I use LEDs in the things I build.

There are many different types of LED based on the chemistry of the substrates in the device. There are several ways to make 'white' light: mainly, either run the photons emitted by the LED through a phosphor coating, [similar to fluorescent tubes or CFLs]. Or to mix the emissions from three or more diodes of primary light frequencies, [yellow/green, red and blue for light, as opposed to the paint primaries we learned when daubing at first grade], to create a 'white' light. The percieved 'temperature' can be adjusted by changing the frequency of the photons emitted, to give 'warm' or 'cold' white. The problem is balancing the emitting power against the temperature of the device when running, because the life deteriorates exponentially with temperature. Don't confuse working temperature with power-loss inefficiency. The working area in the LED is very small, say 1mm2, and it's hard to get the heat away from that small spot.

In practice, the outut from individual units is presently so small that they are most often fitted in multiples. Switching out some of the lamps is then probably the easiest way to create mood lighting effects. Colors are true, as Greg says, because the frequency of the actual light emitted can be controlled electronically.

The problem with all these 'high tech' light emitters is percieved color of the 'white', deterioration in brightness over the lifespan [L50] and cost effectiveness. Manufacturers 'get away' with low brightness, because humans compensate for low light levels so well. A 50% drop in output [ one 'stop' to camera buffs] can be compensated by the eyes and brain so well that we barely notice. Except when we need the brighness for fine work or reading, when the opening of the iris to let in more light interferes with focus and ability to see detail.
Here's a good article:
http://en.wikipedia.org/wiki/Light-emitting_diode

LEDs are usually dimmed using PWM, not by reducing the current through them.