Tagging On US Stamps

Hello, I am new to tagging or checking for tagging on US stamps and I wonder if I could get some help with it. By chance I came across a Raytech LS-4 before I even knew what it was used for, so I have a good light. I have spent some time reading and I know about the danger of using these UV lights, to your eyes especially. My problem is that I have only checked a couple hundred stamps and I seem to be having trouble with some of the white or light colors. Often times I can see colors on the edges of blocks which I assume is a tell tale sign of tagging like they just didnt go all the way to the edge? or sometimes it looks like they only did the edge? I have an INTERPHIL stamp, which is white and I was able to check that against another stamp I had to be pretty sure it is not tagged. Presently I have stamps # 1455, Family Planning and the Antarctic Treaty from 1971. I see no sign of tagging on a plate block or on a single from another source. I know it would be pretty rare for me to have both untagged so I am doubting what I am seeing under the light. I have also read about looking for the glow after the light is turned off but I am not having much luck with that either.
In a slightly different matter, my light only turns on after about 3-5 flicks of the switch...I know these bulbs only last so long so is it the switch or the bulb that is going?
Thanks in advance for any help you can offer, Dave

I don't know if this will help at all - it's entirely possible that your lamp uses a different power switch than mine does. I have one of the Raytech dual bulb UV lights. Each bulb has its own power switch, a button that is pushed directly down with a spring inside to return it to an upper position. To turn the light on, I have to hold the button down for a second or so to get the lamp started. The same button turns off the lamp, although that only needs a quick press to turn it off.

If I try to start the lamp with just a quick click, nothing will happen. My lamp has been that way since I first bought it (must be 25 years old by now). If you have the same sort of button starter, you could try holding the button down for a second or so to get the lamp glowing before releasing the button.

Also, from your description of "white" tagging (I think that's what you're talking about), I would guess you're using the wrong wavelength on your lamp, which is supposed to have a switchable filter to give you two different wavelengths. US stamps should glow green for normal postage or red for airmail stamps. If you use the wrong wavelength, you won't see any colour in the taggant.

Ryan

Hi Ryan, I think you are right with the switch type, though after it was warmed up for a few seconds it will turn right off and on with a quick click. Either way that was very helpful to know. Also I have the type of light where you slide the black plastic bar across the openings on the bottom of the light which makes it so you can use either light type or both at the same time. As for the "white" tagging, I am sure I have it on the correct setting because most all of the other stamps glow green as they are supposed to and also when I move the bar to the other side I cant see any colors.
Another interesting thing is that with the last batch of plate blocks I checked I didnt determine which ones were tagged and which were not (as they were produced originally), as a result I found that I chose correctly as the ones I deemed as tagging omitted were in fact never tagged to begin with. This gives me some confidence that I am doing it correctly. I just wish there was a better way to be sure rather than spending $20+ sending the stamp out for a certificate. I did recently read an experienced stamp person claiming that the Raytech brand light which I have is "the best".
Thanks Ryan, I do appreciate your input. Dave