Normal film capture light in the visible spectrum, IR film capture light in the very end of visible and the IR range ( not emission type ). As almost all natural scene goes, the intensity of visible spectrum and IR is pretty much equal and roughly linear. I think you have confused IR film ( whoich do not record IR range, but insdtead record Near range infrared up to 1 Micron, a sizable chunk opf visible spectrum, and most of all also UV spectrum ) with real IR capture whioch require both near rane and Far end IR range ( up to 10 or above micron, typically associated with heat emission ).|
Thus if there is a scene that require certain EV value for visible light, its almost always that IR capture require an exposure of similar EV. As a general rule, there will be very minimal deviation ( usually less than 2 EV ). However, the inclusion of the RED filter on camera will reduce the in camera TTL by a wide margin as the meter is corrected for visible spectrum opnly and the filter will further reduce the light by 2 to 4 stop ( depending on what kind of filter )
So the normal way to meter is to figure out the difference. In bright sunny situation, this is pretty much just stright forward as the broad spectrum of IR and Visible is just about the same. In shade, the usual case is IR ( as in low K vlue spectrum ) is reduced ( usually by 0.5 to 1.5 EV ) and thus require an exposure correction of such. During early morning and evening when Sun is at low angle and light is shifted towards the low K range, the IR emission tend to run instead to 1 EV above visible or similar.
With these general idea. One can usually meter ( with no FILTER ) as usual and use that exposure as starting point and correct for exposue. The thing that one need to consider is though Metering on normal camera / Hand held meter is such that it is calibrated to a visible reflective. While in nature, any Flora Tend to reflect IR far higher than usual. That is the general idea, and in praktice, we have to consider that most lens simply do not let in near range IR as linear as visible spectrum, and of course do not focus proper either. SO the best approach is still meter and bracket ( good IR photographer usually take a ascene and bracket out to 2 EV or so ). There is no way to avoid such hassel as IR is not measurable by normal metering equipment and all must be done via experience and guesswork. That is why I think in the long term, IR in digital is far more useful than Film as it offers some form of inetractive check up with the capture and exposure .. )
Again I must stress the best technical source is to fromt eh Mfr .. check this 2 page
http://www.kodak.com/global/en/p ... .14.19.22&lc=en
http://www.kodak.com/global/en/p ... hPubs/f13/f13.jhtml