..lamp itself is only 700kb.

Yes, smaller size (if not small [:)]) helps. But the light-sources still take their toll on a slow computer. Actually the .png appears to constitute most of the size. I had a quick look and if I understand correctly the .png uses a palette with partly transparent colours(?) as there seemed to be no transparency in the .mtl file. The effect is very nice even if the bulb will remain slightly too visible in rendering (at least until other decorative/ambience light-sources are added to the plan). And this is the essence of my problem - getting the .mtl transparency to balance with the .png to create a good "frosted" look like a real lamp-shade.

And I agree with MartinSK, it is a very nice lamp that deserves to be part of the collection (preferably with pre-fitted light-sources). And clearly, as you have demonstrated, using your techniques it is certainly possible to create the beautiful images.

..top and the bottom, should not be tinted.

No, of course not. It is clearly no problem to use various colours in the different light-sources in the model. But the trouble is that the colours will stay fixed even if I change the hue of the texture.

The lamps are really just props.

Ah yes, this is certainly true if you want to create beautiful renderings. One will need to cheat. However, from my perspective when I do real life redecoration, I move lamps and light-source continuously and my purpose is only to do very quick tiny renderings to get a general impression of how the lamps can work in the room. In other words, my aim is not picture perfect lamps and perfect renderings - it is to produce a quick and good impression of light in the room, straight out of the box, so to speak.

But I have a couple of ideas that I might try if work and other minor annoyances did not keep interfering...

ok