The Same Light for Less — Filament against LED
Two lamps stand in a dark room under one rule: both must give exactly the light you ask for. That fixes the useful output and leaves only one thing to compare — what each lamp has to be fed, and how much of it ends up warming the room instead. The two Sankey diagrams above them are drawn to a single shared scale, so their widths can be compared by eye.
Como usar esta simulação
- Useful light you want — the single slider, 2 to 15 W of light. Both lamps deliver it; only their electricity bills differ.
- Drag anywhere on the scene to look round the room.
O que observar
- The two yellow light arrows face each other across the middle at identical widths — that is the condition being held fixed.
- The violet input band under the filament is four times the width of the LED's, at every setting of the slider.
- On the filament, the heat arrow is nearly the whole band; on the LED it is the smaller share. Read the diagrams, not the bulbs.
- The glass temperature beside each lamp follows the waste, not the light: a filament bulb is too hot to touch and an LED is not, even when both are lighting the room equally.
A física por trás
Supply either lamp with 100 J of electrical energy. A tungsten filament transfers about 10 J as useful light and dissipates the other 90 J to the surroundings, mainly as thermal energy: η = 10%. An LED transfers about 40 J of the same 100 J as light and dissipates 60 J: η = 40%. Turn that round — hold the light fixed instead of the input — and the filament needs four times the electricity, because it keeps only a quarter as much of what it is given. Ask for 10 W of light and you are looking at a 100 W bulb beside a 25 W one, which is exactly the swap households made.