Magnifying Visors

Why does not artificial light going through a magnifying glass burn?

Why does sun light going through a magnifying glass burns, but artificial light, like light from a light bulb, going through a magnifying glass does not? I have done an experiment but could not find the reason why.

Public Comments

1. Well it depends on how bright your light bulb is. You can definitely burn things with light from light bulbs. Bright lamps are used to make CO2 lasers that cut metal so it isn't a limit on artificial light.
2. Because the sun light has many element so can burn the paper, but artificial light only light way so it cannot burn.
3. First off, there is no conceptual difference between sunlight and light generated from a light bulb. It's all electromagnetic waves. The reason is most likely intensity of the light. I beleive the intensity of sun light is around 1.4kW/m^2, and the bulb you are using is probably much less. Try using bulbs with more power. Even better- try it with a laser pointer.
4. If you are using an ordinary tungsten 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.
5. I believe that it's because you are not only magnifying the visible light, but magnifying the infra-red light. Try it with heat lamps and I bet it'd burn.
6. It's just the intensity. You don't realize how much brighter the sun is compared to a light bulb, because your eyes adjust to the difference automatically. The sun is a million times brigher than the full moon, or about 1000W per square meter. To get that from a household lightbulb, you'd have to be like less than an inch away from the filament.