I'm working on a lighting project at the moment, and was wondering if a regular light bulb exists that takes a second or two to "fade out" (i.e. go from on to off in the course of a few seconds). Does something like this exist? I need it to be a bulb that works with a standard screw fitting, any suggestions would be appreciated.
Some halogen bulbs take about a second to stop glowing after power is removed. It's really exponential, though.
you could put a dimmer as the light switch so as you turn from on to off it would give that effect...
I've seen circuits to bring a bulb on gradually with the aim of longer life, and a similar circuit could give a fade out, but for mains bulbs you'll need triac control. Nothing around built-in to the bulb AFAIK but some of the mains touch-switches like these include such features.
Put in a big 240V capacitor in parallel, as though you were using it for decoupling -- but it'd need some sort of rectifier circuit to stop the cap exploding... ch424
http://glolux.com/, but the glow color would be yellow/green and it would take a lot longer than just a second. Else you would have to go to one of the capacitor circuits mentioned above. The energy has to come from somewhere.
Try a search for "keep warm" or "soft start" circuits. They are fairly common in industrial and vehicle lighting. The idea is to PWM the lamp at turn on and turn off so that you reduce the thermal shock to the filament, prolonging its life. On vehicles lamps or industrial lamps that flash rapidly the filament often is only reduced to a barely-visable glow, this is where the keep warm description comes from. PWM circuits have replaced the old ballast resistors that wasted power. The PWM signal generally stays at a ratio that keeps the filament warm but not visable, then increases in duty cycle to the fully on state. The idea is the same as the fan controller circuits. One of these circuits could be modified to give the result you want.
You'll need a very large and very expensive cap if you go that route. A 120uF cap charged to 170v will light a small 4w christmas tree bulb for about a second. For a 40w bulb, 1200uF, and even more for larger lamps! You could use a standard triac dimmer with the control replaced with a photoresistor and a LED in an opaque tube. A much smaller cap can be used to provide the fade effect as it only needs to power the LED.
You could go commercial and try one of the Lutron dimmers. I have the remote one all over my house. When turning off the light they dim for about 2 secs to 10 secs depending on the setting.
