Infrared Emitter Questions, etc.

Hello! I am trying to find a datasheet for an infrared emitter I bought. The manufacturer is Knight Lites. The product number is KIE-7304-1P. The package says: 5mm Blue Clear LED. Infra Red Emitter. Radiant Intensity - 16.1 mW/sr. 1.6V @ 50mA. But it doesn't say the wavelength of the LED! I am trying to find a 940nm LED for controlling TVs, etc. (is that the wavelength most TV remotes emit at?) Questions: can someone help me find the datasheet, or tell me the wavelength of the LED? What is radiant intensity and mW/sr? Do I need a transistor to operate the LED, or can I just attach a 330 ohm resistor to a I/O pin on Arduino UNO? What wavelength do most remotes emit at (940nm)? Thanks!

There's some info about that type of LED here: http://www.transcanadaelectronics.com/view_prd.phtml?cid=014 It says that the 7304 peak spectral output is at 880nm +/- 50nm.

Pete

Are IR photodiodes / photodetectors the same as IR phototransistors? What is mean't by "dark current"? I found out that most IR remotes operate at 850 - 950 nm. So will a 880 nm should work, right? I am planning on making a heart rate monitor by shining an IR LED through my finger, and have an IR phototransistor receive the amount of light shining through my finger (http://www.arduinoevilgenius.com/projects Project 12)

A photodiode acts more as an on/off switch while a phototransistor can report a varying intensity of light.

"dark current" is how much current leaks through the device in complete darkness.

The wavelength is not critical until you're trying to maximize the sensitivity of your receptor. I'd suggest that while you're working on your circuit that you start with a visible red or white LED; you'll find that your phototransistor detects it just fine.

I have a 880nm (+/- 50nm) IR LED. I am trying to immitate the signal of my TV remote to turn my TV on and off! But, I don't know what the wavelength of my TV is, exactly. But, if I want to control the TV, it doesn't have to be EXACTLY the same wavelength (it'll just be more sensitive the closer the wavelength of my IR LED is to the remote), right?

TV remote control works with IR pulse bursts ( of 38 kHz usually ). The "color" (wavelength of your IR LED) is the least problem.

dkl65: But, if I want to control the TV, it doesn't have to be EXACTLY the same wavelength (it'll just be more sensitive the closer the wavelength of my IR LED is to the remote), right?

Right.

Radiant intensity is the light power per solid angle. This is basically a measure of how brightly one can illuminate at distance. mW/sr = milliwatts per steradian. A steradian is the unit of solid angle subtending one square radius at a distance of that radius. Thus 4 pi steradians make up the whole sphere. An emitter of 4 pi watts (uniformly in all directions) would thus be 1 watt / steradian. The sun emits about 3 x 10^25 watts/steradian!

For LEDs this really just tells you how tightly focussed the light is (they only quote the central, maximum intensity). Narrow viewing angles mean high radiant intensities, all else being equal.

For LEDs this really just tells you how tightly focused the light is (they only quote the central, maximum intensity). Narrow viewing angles mean high radiant intensities, all else being equal.

So my 100mW/sr IR LED has more focused light than my 16.1mW/sr IR LED. Therefore, I can not have to point the second LED directly at the TV, because it is more spread out, right? Does this mean that it is also dimmer? Another question: what is the mcd of an LED? If my IR LED uses 1.6V @ 50mA, do I need a transistor and a 88 ohm resistor to operate it, or can I attach it directly to the digital pin with a 100-330 ohm resistor, just like some examples? Do IR Phototransistors look like the emitters (LEDs)? Is the long pin of an IR Phototransistor the collector? Can you use an IR Emitter and IR Phototransistor alone to measure the temperature of an object?