IR wavelength - Lowest non visible + Photo sensors

[karlos]

What is the lowest IR wavelength you can get that is still invisible to view.
I'm need to turn off an a dark sensing photo electric sensor. normally I do this with a 680nm wave length. I believe the photo sensors best wavelength range for operation (turning off) is between 500nm and 650nm

part one. Lowest IR wavelength still not visible?
Part two. Has anyone tricked a standard outdoor dark sensing photoelectric sensor with a 800 - 900nm IR laser.

(( FYI this is not for street lights as in NZ where I life out street lights are on timers. it for a sensor on my own property ))

 

[NightExplorer96]

There isn't really a "lowest wavelength" of IR that is invisible for a persons eyes for everyone, as everyone's eyes are different form one another. Some members here can't see 808nm at all, while others see 980nm just fine(although of course very dim). It's assumed in general terms that 980nm is pretty much invisible to everyone though. 808nm while in the IR range can still be seen as a very dark, cherry red to most people at higher powers

-Alex

 

[karlos]

really appreciate the reply.
I'm OK with a bit of visibly at the pointer end, its more at the end that the laser goes into the sensor.

 

[paul1598419]

Which photo sensor are you using? It should state in the data sheet the usable wavelengths. I don't think they are so narrow as to restrict near IR. In fact, you could use a photo pickup out of a remote receiver that uses IR in the transmitter. There are many of these and they can be had quite inexpensively.

 

[karlos]

Hi, thanks for the reply. Sensor already in place and has no labels or markings. Sensor is on my pole but has a electrical cable from it going to the neighbours which prevents me from replacing it, other wish I would just put a switch on it. I guess I just have to buy a laser close enough and try it. Would love to know if a 980nm would knock it out, was hoping to know whats possible before buying

 

[paul1598419]

What you are talking about sounds highly illegal. I thought this was on YOUR property and had nothing to do with city services.

 

[karlos]

read again Sir
Sensor is on my pole but has a electrical cable from it going to the neighbours which prevents me from replacing it

so from the street, cable comes across my land, to my pole on my land which goes underground to my house, cable goes up hill to neighbours. I'm free to do what I like with the light. in NZ you have to have a qualified electricalian to fit everything and I dont have the money to put into a light I only want off a few times a year.

 

[paul1598419]

Yes, and that is called an easement. That means that though the pole may seem to be on your property, it isn't because the city has the rights to all easements.

 

[karlos]

As much I would love to debate this with you I don't want to get to far of my topic. City responsibility for services in NZ end on you boundary. Then it is up to you as a property owner. so if say i bust a cable over my land, i pay to fix privately as it and has nothing to do with the local council. My neighbour has an easement for the right to convey power across my land. so from my pole to his, the cable is his and rightfully so. I'm only interested in my own light, on the pole.

if you have nothing else of value to add please respectfully move on. I do appreciate your first comment which was of value. thank you

 

[Rivem]

Yes, and that is called an easement. That means that though the pole may seem to be on your property, it isn't because the city has the rights to all easements.

I don't really understand what karlos is explaining, but it is fairly common for electric utilities to attach lights to their poles with no interface to the property for customer lighting. It's usually a rental attached to the electric bill.

The big question is whether or not karlos owns/rents this light.

As for the question, a laser that you can't see wouldn't be good for this at all and would be too hazardous. These light sensors also usually have serious ir filters on them anyway.

 

[karlos]

see above.
no rental, ownership with an easement for the neighbour... feel free to chip in anything form my original question. thanks

 

[Rivem]

see above.
no rental, ownership with an easement for the neighbour... feel free to chip in anything form my original question. thanks

Read the rest of my post. You'd be best off with some other method like a small remotely activated spotlight to hit the sensor. The ambient light sensors tent to be more sensitive to 405nm which isn't that visible to us. The IR laser would almost certainly be a waste.

 

[karlos]

apologies I miss that part of your comment. thank you for the feed back.
am keen on something not visible. I'm trying to lose the light for view of aurora australis a few times a year. but otherwise the light is very useful to me

 

[RedCowboy]

Duct tape a flashlight to it?

If it's ok with your neighbor maybe just set this in front of it?

http://www.ebay.com/itm/2pcs-48-LED...105311?hash=item51d80d5c9f:g:yIMAAOSwFdtXyEAk

Or if you and your neighbor really don't want to see any pink glow you maybe could set this in front of it...at your own risk.

http://www.ebay.com/itm/Invisible-i...999635?hash=item33ca0a38d3:g:N7MAAOSw~AVYv5pj

 

[karlos]

Im looking at a different kind of cell. the most common is: disclaimer I have limited knowledge of this and have looked around the web a lot, hence why Im her talking to people that know these things.. and hey learning a lot as I go )

The Light Dependent Resistor

a light dependant resistor
Typical LDR
As its name implies, the Light Dependent Resistor (LDR) is made from a piece of exposed semiconductor material such as cadmium sulphide that changes its electrical resistance from several thousand Ohms in the dark to only a few hundred Ohms when light falls upon it by creating hole-electron pairs in the material.

Typically then, it has a peak sensitivity wavelength (λp) of about 560nm to 600nm in the visible spectral range.

Nothing illegal here. nor would I condone it if it was.

 

[Rivem]

apologies I miss that part of your comment. thank you for the feed back.
am keen on something not visible. I'm trying to lose the light for view of aurora australis a few times a year. but otherwise the light is very useful to me

Understandable. Like I said though these light sensors are usually filtered very sharply on the red end of the spectrum unlike camera photosensors. If they're going to detect IR, it's going to be very close to the red. Probably would have to be below 800nm if it'll work at all.

That said, near-UV is a good option for this. You can easily get 405nm lasers or flashlights even lower that wouldn't interfere mu h with your view at all. A 365nm flashlight would be hardly visible, but I'm not sure how well it'd work.

Folks in my astronomy club usually use 532nm, 405nm, or 445nm to disable sensor lights with okay success.

Edit: just to be clear, yes your sensor has that sort of performance, but they very commonly have a plastic filter over them to keep them from responding to certain wavelengths.