dim-up a lamp automatically, slowly?

[likeguymontag]

Another aquarium question for you all: My fish tank has something on the order of 100-120 watts of fluorescent lighting over an area 30" by 12", so it's pretty bright. I want a gentler transition from light to dark and dark to light than I have now, 'cause when the lights go on suddenly it seems as if the fish freak out a bit.

My goal is to design some kind of lighting that I can use to simulate dawn and ideally dusk too, something that would gradually fade in and out. I don't care what the light source is, whether it's incand, led, fluoro, whatever, so long as I can get the dimming effect automatically on a timer.

There are lots of options for dimming out there, but most of them are just rheostats and don't have any capability to be programmed or adjusted. I want a very slow ramp rate, something on the order of an hour would be ideal, but I'd settle for five minutes, and hell, I'd even settle for ten seconds if it were easier.

So what are my options? So far the only things I've discovered are super-expensive dawn simulator alarm clocks for treating Seasonal Affective Disorder and similarly expensive programmable lightswitch dimmers from the home automation category, some of which use X10.

I'm not afraid of soldering, but PIC programming is out. Thanks for any ideas.

[tanawah]

Take a look at some of the automotive courtesy light project kits. As I recall they do a soft start and a soft stop. Would need some changes to resistor values to get your hour effect. I would look at power LED for the light emmiters. The courtesy light kits would be around 3 watts so you would need to have a higher power drive transistor. there was also a flickering flame circuit around that used two 555 ics. I expect a modification of this would be fine. You would only need one 555 for what you need. When you shut it down you would need a switch at some point to shut it off completely.

Maybe a multi timer board? Here is AUS they are around $20 for a 4 outlet version. You could have 16 levels of lighting. The means to do this would be to have 4 sets of lights. say 2 watt, 4 watt, 8 watt and 16 watt.
Switch as follows
1. 2w - 2
2. 4w - 4
3. 6w - 2+4
4. 8W - 8
5. 10W - 8+2
6. 12W - 8+4
7 14W - 8+4+2
8. 16W - 16
9. 18W - 16+2
10. 20W - 16+4
11. 22W - 16+4+2
12 24W - 16+8
13 26W - 16+8+2
14 28W - 16+8+4
15 30W - 16+8+4+2