Looking for a cheap and cheerful IR light source

thatmattrogers

Hi everyone,

I'm experimenting with Tracking for a small community project with very little budget.

Because there's quite a lot of ideas floating around where the projection will interact with performers I feel like IR might be a good solution but we don't have access to much equipment.

I have a full spectrum camera and an IR filter so that part should be fine, but I was wondering if people had found any cheap and cheerful off the shelf IR lamps that would do the job sufficiently.

As we're going to a couple of venues I'd rather bring something with us than rely on filters since I cant guarantee that all of them will have similar equipment and that their lamps will behave in the same manner. (I get a little paranoid when it comes to mission critical equipment, I would kinda prefer something cheap with known limitations than have to problem solve for an unknown element)

Thanks.

Woland

@thatmattrogers

There's the option of just combining lighting gels to filter out everything other than IR light. Here's the info I got from the magnificent @primaldivine when I was just learning Isadora back in 2014:

Standard theatre lights focused on the back wall, with lighting gel filters added to each light: Roscolux 19 (x2)) Roscolux 83 (x1) Roscolux 90 (x1)
These four gels will cut out the visbile light spectrum but allow the IR light to still shine from the theatre lights.
NB DO NOT USE THE LIGHTS AT GREATER THAN 50% or they will melt.
Always check the gels often for heat damage and replace as needed.

mark_m

@woland

Mark goes into detail on the process in this video from the Werkstatt in 2016

@thatmattrogers

I bought four of these from Amazon the other year, and they work fine in a small area. I used them with a hacked CCTV camera with sub-SD quality output. Good enough for basic tracking under theatre lights BUT you have to hack them: they only turn on when the sensor in the centre says it's dark, so you have to unscrew the top and cover over the sensor which is in the middle of the LED array.

thatmattrogers

@woland y fear is that as venues switch to LED based lighting there will not be significant IR output from the newer fixtures and I don't want to encounter that on a performance day without time to come up with a solution. That's why I'm looking for something that I can bring with me without relying on in house venue equipment.

Any thoughts?

thatmattrogers

@woland I found a pretty low cost IR led floodlight that's made for CCTV applications.

I'll have a little play around with them and report back in case my findings are useful to anyone. I suspect I'll need to improvise some barn doors but otherwise this seems like a path to something.

CitizenJoe

@woland said:

Roscolux 19 (x2)) Roscolux 83 (x1) Roscolux 90 (x1)

It's inferred above, but the gel option will NOT work with most LED lights [edited - sorry].

That said, the cheap amazon type options do work well. Just make sure that the wavelength of light output from the fixture matches the wavelength that your camera is looking for.

Cheers,

Hugh

thatmattrogers

@citizenjoe They're advertised as 850nm and I have an 850nm filter for the camera, so hopefully both companies are telling the truth.

fingers crossed on that one.

dbini

i have a few of those CCTV IR floodlights but they are quite difficult to work with. the IR is generally produced by an array of LEDs each with their own internal reflector, so the beam is difficult to focus, even with a custom barndoor system (I mounted mine inside wooden boxes).
I have used them to light a performer for tracking from an overhead camera (b/w industrial USB cam with an IR pass filter) but it is difficult to prevent spill onto the floor and the falloff is quite steep. I ended up using 3 or 4 small units to light a 4.5m circular stage area.

If you do try this kind of solution, remember to put some gaffa tape over the light sensor so that the unit thinks it's always nighttime.

i much prefer using combined lighting gels with a halogen profile, but its not very sustainable - the wider the beam, the closer the lamp to the gel, the quicker the gels burn out, even when running at 25% max brightness, so i have needed to use at least 4 lanterns to cover a stage.

in an ideal world, there would be an IR version of a COB LED profile lantern, but it's a very niche application, so i don't expect they would ever be easy to find.

Fred

@thatmattrogers

As al you really need is contrast you can also opt for lighting the floor and not the performer with IR. This does require that your visible lighting for the performer and anything else in your set has minimal IR (or better yet none) content.

You will also see a great improvement if you camera also blocks visible lighting using an IR pass filter. Not many IR cameras have this built in, but Midwest optics sell a variety of filters you can put over your camera lens.

Using these I have had good results getting solid reliable tracking of movement from above. Ie using cheap IR floods to light the floor and not the performer.

CitizenJoe

@fred said:

<p>@thatmattrogers</p><p> but Midwest optics sell a variety of filters you can put over your camera lens. </p>

This is what I use; Lee 87:

thatmattrogers

@fred absolutely, the plan is to use a Sony a5100 that has had its IR and UV cut filters removed from the sensor then add an 850nm filter onto the lens.

So in theory, if both the LED arrays and the photographic filter have both been sold with accurate information. I should get a very clean 850nm image.

Here's hoping.

thatmattrogers

@citizenjoe like I said above I'm ideally looking for a solution which doesn't rely heavily on in house fixtures, but it's good to have this info as a back up.

thatmattrogers

@dbini good to have a heads up from someone who has worked with LED floods, I'll be your thoughts on mind whilst I'm problem solving.

I won't have the same problem with exposure since I'm using a camera capable of manual exposure, but it's definitely worth putting on people's radar if they're using this fire reference later.

Fred

@citizenjoe yep, but these are not great for optical transparency for cameras.

https://midopt.com/filters/bp8...

These are made for moutning to cameras, so no leaks and wont distort the image either. Habign said that in a pinch the lee filter will do.

Also if there i the opposite availble - filters for lights that will block IR these will be useful for better isolation - so that your visible lighting does not mess with the IR lighting.

CitizenJoe

@fred said:

@citizenjoe yep, but these are not great for optical transparency for cameras.

True, but for what I use it for (tracking) it doesn't matter. They are a cheap and cheerful alternative!

Cheers,

Hugh