Quite right JiK, but the point I was trying to make is that it's the AC that's being controlled- so with LEDs or other lights that go instantly on/ off the dimmer will produce unpleasant flicker at 100/120Hz. With incandescents the thermal inertiaof the filaments is enough to mask this effect.

It's quite possible to make HF pwms that won't flicker, but in these days of costs pared down to nothing, they won't happen until the market's hand is forced.

Another thing that annoys me is the difficulty of comparing specs when some units are quoted in candelas, others in lux, others in lumens, others in watts/ square metre, and yet others (the incandescents) in just watts. These all measure different aspects- the consumer only needs four parameters: How much visible light it emits, what is its angle of illumination, what colour(s) is the light, and how much power it takes.