Robert Monsen said:
But eclipses and airplanes would be fun.
ha! actually it *would* be great if the lights dimmed a little when a
plane flew overhead! i'm thinking simulated shadows?
you guys may think i'm a little crazy for wanting my lights this way--
ok, i may be crazy, but for entirely different reasons.
here's a little more background, hopefully to put things in better
perspective: i have regular lights/lamps in the room, apart from this
project. for this project, dimmable flourescents will be mounted in a
"light box". this light box will actually be an old window i'll be
hanging on the wall, with a reflective box framed behind it (open to
the glass in front). the lights will be mounted behind the framing of
the window, the plan being that you won't see the bulbs, but only the
light. think "hangable" windows, with real light shining through. i'm
using flourescents because the natural-sunlight models are much closer
(in color) to real sunlight.
now back to the gritty. i've been reading up on voltage dividers and
op amps, but they only seem to apply when you want to change or divy
up the voltage of a known voltage source. the dimming control of the
ballast i'm using has 2 wires out for a 0-10V, .5mA, class 2(DC)
circuit. this is a voltage source built into the ballast. i can dim
the lights by adding a 100k trimmer to these 2 wires. i was measuring
today and found response on the lights came from a resistance between
15k and 75k ohm (the higher the resistance, the brighter the light).
this didn't make sense to me because when I did my equations (V=IR) I
thought response should have been when R was between 0-20k ohm. i
figure i didin't consider dynamics in the ballast or internal
resistance or one of a million other concepts i've never heard of.
the LDR, hooked in series with a trimmer on these 2 control wires,
makes the flourescents go dimmer as light hitting the LDR gets
brighter-- i need it the other way around.
i really like the idea of having an inside LDR and an outside LDR
balance each other out, because (1) i don't think i'd ever get a
linear response otherwise and (2) this will eliminate problems with
the resistance of the outside LDR changing when it get's wicked cold
out. (i understand other inside lighting may interfere, but creative
placement of the LDR should fix that.)
BUT... it there a way to do this not with voltage, but with
resistance in to the ballast control? from your suggestions maybe the
ballast 0-10v controls hooked up to one side of an op amp, a similar
but steady vcc hooked up to the other side, both sides with LDRs in
series and whatever necessary trimmers/resistors-- but how would this
raise or lower the voltage of the ballast control wires?
sorry, i'm a little dense. but i'm slowly learning