NO, ever compared reading through a filter to the filter factor? Because light meters do not react to the spectrum the way film does, the results are different. I have compared both and for other than sky light filters and polarizers, stick with the filter factors.
Even though filter factors are supplied with the gels, it would seem the factor would vary with the distance and intensity of the light source. I guess I could take a reading of the ungelled light and reduce that by the corresponding gel factor, It just gets complicated with multiple lights.
I've got to chime in here...
Yes, meters respond differently to various colors than black-and-white film does (with the possible exception of the Zone VI modified meters). However, filter factors are similarly imprecise; they are not calibrated to a specific film and are figured using a specific color temperature of light (usually average daylight), which may or may not be what the photographer has available.
As far as using hot lights... Filter manufacturers used to give "tungsten factors," since the filter factors for many colored filters is radically different under tungsten light than daylight (the usual calibration standard). Factors for red filters are much less under tungsten light; green and blue filter factors are much greater. Unless you have the tungsten factors for the filters you are using and know the color temperature of your lighting (2400k - 3400k for different types of photofloods), just applying the filter factor may end up with an exposure that is way off.
I've been reading through filters for years with success; better exposure accuracy than just applying factors. The trick is to do a bit of calibration and come up with an exposure compensation factor for each filter/film combination. Note that the factor will be film-specific, since different films have different spectral responses (that's why factors are inaccurate...). I've found that the weaker filters, like #8 yellow and even a light yellow-green filter (XO) don't need much compensation, so one could start calibrating with the strongest filters first to save a bit of time. A #25 red filter needs both exposure and development changes from "normal" for me; less development with TXP, but more with TMY. It seems the way the film is color sensitized affects the contrast when developing as well.
The procedure is simple. Take a reading through the filter, make an exposure using that and bracket on either side by a stop. Make two of each neg. Develop one set as you usually would for the subject-brightness range of the scene and make some prints. If you find you need more or less development for your best exposure, make the appropriate change for the subsequent neg.
One could just take a reading, make a negative and see how it prints and then make whatever extrapolated adjustments one thinks are necessary for the next photograph. By keeping good notes, one could zero in on the right compensation in just a few sessions.
Since gelled lights work on the same principle as colored contrast filters, the same method works when using them. A couple of tests with the filter/film set up and one should be able to simply read with the meter and apply the compensation factor.
[Note: light-to-subject distance changes the intensity of the light reaching the subject according to the inverse square law, but the color temperature of the light remains the same. Whatever factor works at one distance will work at another.]
Best,
Doremus