If you are using an ordinary ttugsnen filament lamp (preferably with a clear glass bulb) then a 150watt bulb will put out around 15watts of light in the visible range, a glass magnifying glass will not pass much infra-red so you really are comparing about 15 watts from this bulb with what you can get from sunlight(in the visible range) this is more than 800W per square metre.With a small glass, say 5cm diameter, you could focus about 1.5Watts power to a very small spot using sunlight (it comes in almost parallel from a very distant source).To get to half a kW per square meter at your magnifying glass you need to be much less than 5cms away from the filament of the 150Watt bulb and you can't focus the filament image down to a spot at that range.