LED driving

[Um...Me123]

Say you drive a LED only 50% of the time do you just multiply the amperage by 2 (when you want to)?  Is it that simple?  Then you can apply this idea to other concepts when driving LEDs.

 

[audioguru2]

Yes, the brightness of an LED is determined by its duty-cycle. If it is switched on and off at a frequency high enough that it doesn't appear to flicker, if it is on only half the time then its current must be doubled for it to appear as bright as one that has a steady current.

Pulse-width-modulation is used to efficiently dim LEDs. With a narrow pulse width it appears dim, with a wide pulse width it is bright.

 

[Um...Me123]

If you have a video camera that has "Night Shot" or similar, will Infared LEDs work like invisible flashlights for the camera?  Can you just use a 555 to drive them 50% or do you use somthing else?  I don't know anything about oscillators (sp?) and just a little about 555s.
Thanks

 

[audioguru2]

Many video cameras are sensitive to IR. If you modulate an IR diode with an oscillator, it will interfere with the frame rate. Just power the IR led with direct current. You might need a bunch of them for enough IR brightness.

 

[Um...Me123]

I was looking on ebay for IR and UV LEDs.

 

[audioguru2]

Hi Um...Me,
You and your suppliers are mixing up technical terms.
90mW is power.
940nm is wavelength which is frequency which is colour.
10m, 20m and 100m could be anything, but not distance.

Maybe "red glow" LEDs operate at a high IR frequency close to the frequency of red light.

UV LEDs aren't efficient. Since they operate at the very high frequency above purple and getting close to xrays, they damage living tissue such as eyes and skin.

View attachment 37672

 

[Um...Me123]

When I meant efficient I kind of meant the oposite but thats fine you answered my question anyway.
So if the LED can damage skin that's why they arent used in effect lighting then and neon and incandecent are because they are lower frequencies.  What are uv LEDs used for then?  So you can make you own home CSI light?  (I guess that explains why regular black like tubes don't work very well like you see on tv...lower frequency.)

 

[audioguru2]

UV isn't light, it is radiation at a frequency higher than visible light. It makes things like some laundry detergent "floress" or make their own light. Florescent light tubes have a white phosphor that glows when the UV inside radiates on it.
"Black light" bulbs have a black filter to try and absorb some of the dangerous higher frequency UV rays.

 

[prateeksikka]

hi audioguru!
i guess nowadays we hardly use LEDs with the invent of laser diodes even in optical fibers
;D

 

[audioguru2]

Hi Prateek,
LEDs are getting better and cost less. All traffic lights in my pretty big city are LEDs. They are going to convert the bus shelters to solar-powered LED lighting. My city gave away LED Christmas tree lights and they save a huge expense in power.
I can't use my laser pointer as a flashlight, but use my blinky LED project on walks late at night and when I barbeque. ;D

 

[prateeksikka]

while the context i was talking about Laser Diodes being used as sourced of power for optical fibers...
in communication links.
;D