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re: New Tank!
>The skylights make the space very bright, so that artificial lighting is
>probably only going to be needed to extend the photoperiod during the
>winter, and maybe augment it a little for plants that need especially
>bright light. I was hoping to put together a controller that would
>bring the lights on if the light intensity in the room dropped below a
>preset threshold. Can anyone give me input on what I need to look for,
>or where?
Remember that the reflectors for your MH lights will tend to block a
significant portion of the light from the skylights. At the very least you
will have shadow areas in your tank.
Depending on your expierience with electronics, there are several ways you
could control the lights based on ambient lightning intensity. I would use
a photocell, small transistor, and a solid state relay. By using a
potentiometer it would be possible to adjust the device so that the
transistor would trigger the solid state relay at a specific light level
present on the photocell (photocells change resistance with a change in
light level). I leave a lot out though, like a little power supply for the
circuit and...
It might also be possible to use one of the devices sold for use on outdoor
light fixtures. Most are intended to turn lights on when it gets dark,
although I have seen some that can turn lights on when it is bright or when
dark (two options). These devices are usually intended to run incandescent
light bulbs though, unless you get the commercial units that run things
like streetlights. The reason this is important is that you will be
switching a big inductive load -- your 2-3 ballasts. Lots of smaller power
switching equipment can burn out with such loads. You will need to use a
relay or solid state relay (preferable a back-to-back SCR version for
inductive loads) to actually switch the ballasts on and off, and just use
the photodetector device to control the relay. Email me off-list if you
would like some possible sources for parts.
The easiest way might just be to use a timer and adjust it so that it turns
the lights on at the time when the ambient light level is at the particular
level you want. You would need to adjust it several times a year to
compensate for seasonal light level variations, but it's lots cheaper and
easier than the "fully automatic" route.
-Bill