Invisible infrared lamps...

[Externet]

Hi fellows.
For an experiment at my workplace, am trying to find an IR infrared invisible light bulb of about 50W? capable (with lenses) to project 1m² of its intense 'light' to a 20metres distant wall.

Reading and searching, cannot find such IR-only lamp source other than wimpy LEDs.
Does anyone has a suggestion how to locate such animal ? Unsure this thing will work :
http://www.gilway.com/shopping/shopexd. ... 053&cid=54

How should be done? -a plain light bulb and an IR-pass filter instead?-
I bought two dozen 50mA IR LEDs, wired them but am not impressed. I see the projection with an IR viewer.

And a doubt... The light Kelvin temperature is just another way to express a color other than its wavelenght, is it? Like 740ºK ~= 940nm ¿?
Thanks,
Miguel

[Chris Smith]

The only way I get huge sources of Lower frequency IR to project is to use a standard light bulb and the IR lens. [Less than 1000nm]

There are IR sources that do better than halogen or the heat lamp, but your main problem with IR is that of heat, pure and simple. All bulbs will burn out the lens if left alone?

If you want to purchase a IR diodes of 50 watts, expect to pay a grand or more.

What I have done in the past is to use a IR lens, cooling, and a standard source to produce the IR beam, and also use a lens if you want to focus.

My best effort was a 100w halogen light with parabolic adjustable lens, IR filter, and a super chiller to stop the light source, the lens, and the IR lens from burning out. [heat]

But if you have the bucks you can purchase the inexpensive IR modules that go all the way to 1000 watts and more and at most frequencies.

The poor mans IR unit is the cheap 1,000,000 cp unit, IR lens for a minute or two, and the IR scope.

Great for night viewing where others think they are in the dark.

But, IR heat will toast this lens in a minute or more.

Dont forget, most IR usage is well below the 1000 nm, in the 780 to 900 nm range, while IR goes well into the 1500nm range where most dont dare because it can become MW. [Flir]

[Externet]

Thanks, Chris.

My alternative is using a plain slide projector with an IR-pass filter I do have from Edmund Optics.

There is a part I do not understand: ¿ Why would the filter need cooling (ventilation) if it is an IR-pass filter, it is not supposed to be a 'heat' barrier, but to let the heat pass ?
Of course I will test, if needs cooling, cooling will get.

Miguel

[dyarker]

The visible light not being passed through the filter is converted to heat in the filter. And, the filter is most likely bandpass, so IR with a wave length longer than the filter will pass also heats the filter.

[VIRAND]

Try dimming a 300 watt light bulb to the point where it is almost out except for a faint red glow.
50W of power might be about right for the effect.

I first noticed that video cameras can see infrared while doing something similar.

[Chris Smith]

The filter frequency is quite small where as the bulb frequency is quite wide.

All energy that doesn’t go through the lens has to be blocked and absorbed by the filter, therefore it gets hot. Cooling is needed if you don’t want the film or chemical to blister or crack.

Lowering a large bulb to a small glow will produce a very good IR, but not the power level you seek.

A moderns Camera can see a lot of the IR frequency while Leds only produce a narrow band of light which is why they don’t get hot when they are in the Ir.

If your into it and you really need a lot of IR, try using five to ten laser diodes at 780nm with collimating lens, [and adjustability] and use these multiples as your light source. But you do need to know the principles of collimating, focus, and mechanical skills.

[jwax]

What ya doing Miguel, checking out the neighborhood at night?
Your IR filter will be fine as long as you have plenty of air blowing at it from the lamp side. It doesn't have to be too close to the lamp either. You'll probably have to build a shield of some sort to block the visible from escaping, just keep the air flowing.
Color temperature is weirdly different than "color", or wavelength. A low color temperature is red, while a high color temperature is blue. Seems ass-backward, but Wikipedia explains it pretty well.
BTW, I've been playing with a .0003 lux video camera, and man that thing sees in the dark! I see stars at night on the monitor that are totally invisible to my eye. Yeah, it's way more sensitive to the IR than my eye too!

[Chris Smith]

The best night vision is the low light camera with several IR lasers and with adjustable lens.

I can spot light the object [like a foot ball field] up to a mile away and see it with the camera in the dark.

If I want to go further than this, say 10 miles or more, then you need a telescope on the camera instead of the general lens and preferably a larger IR laser or several more diode lasers.

My first experiment was with the Celestron C-90 scope, and the view at one mile was like the back of my hand! As good as the first Gen night scope with lens.

I could read single letters of graffiti off the wall at these distances.

[Externet]

Naaah, nothing interesting in the neighborhood.

Tried with the slide projector, has a 300W lamp in it, and my IR filter stays cool as a cucumber. So far, great. Next week I may present the contraption.

The slide projector light goes first trough a plano-convex lens, then a ¼" flat greenish glass disc and final is a double convex lens. Next, it gets into another sliding set of lenses for focusing and ranging.

What would such greenish -cheap bottle glass looking- plano-plano 'lens' would be for?

EDIT- added: Found the greenish glass. It is an infrared blocking filter. Time to remove it and try again :
http://www.exploratorium.edu/light_walk ... _todo.html
End edit.

Miguel

[Chris Smith]

I love turning night into day, especially when your the only one watching.

Distance is really fun.

Sometimes you have to travel?

Often, you have to skirt the law?

Just dont get caught?

Sound at distance is also fun.

Parabolic mirrors, amps, and filters.

[rshayes]

The "flat greenish glass lens" is probably an infrared absorbing filter.

Operating a normal light bulb at lower power (lower temperature) may be a good possibility. It will also greatly increase the bulb life. Quartz-iodine lamps won't be suitable for this type of operation since they depend on high operating temperatures for the process used to control tungsten evaporation.

If you are using a silicon based detector, the peak sensitivity will be around 900 nm. Sensitivity falls off very rapidly for longer wavelengths. The filter used to make the light "invisible" is probably designed to pass wavelengths longer than the 700 to 800 nm range. Any extra energy at shorter wavelengths will only heat up the filter.

A bank of LEDs emitting in the 800 to 900 nm range would probably be the most efficient source, since all of the emitted light would be usable and would not require a filter. An incandescent bulb at reduced temperature might produce more power, but some of it will be absorbed in the filter. There is no point ot operating an incandescent bulb at normal power, since most of the increased emission is at shorter wavelengths in the visible region and will have to be filtered out.

[dyarker]

If rshayes is right (his edit, it is) about the flat greenish lens being an IR filter, and you want IR, removing it will give you more IR. Caution - this may overheat the double convex lens.

[jwax]

Clarification on "IR filter"- Normally this would mean that the filter "filters" out IR, like your greenish looking lens.
Another meaning of "IR filter" is like used in the filters placed over headlights of jeeps in WWII to block visible, but PASS IR.
Miguel- You should get a brighter IR image by removing that greenie glass.

[Chris Smith]

All filters are designed to either block or pass a given frequency of light or energy.

Removing one filter like the green one that blocks the upper heat levels, as well as the general IR range "that contains most of the heat" might now transmit this unwanted heat and frequency to the lens or filter?

Microwaves which are also UPPER IR waves are used to heat objects. Blocking these reduce heat.

Also any energy of most frequencies that becomes blocked by a filter MAY produce unwanted heat from escaping.

[ecerfoglio]

In a slide projector, the IR filter protects not only the lenses (glass) but also the slide from the lamp’s heat.

So, if you are not using any slide it’s probably safe to keep it out - Just check if the lenses (or any plastic part near them) get too hot.