jw,

Most standard dimmers are have an SCR (silicon controlled rectifier) which dims by altering the AC waveshape. Most CFL ballasts cannot handle a distorted waveshape and will not work or die (and really not work). The life of most any type fluorescent is determined by the on/off times, so they are not recommended to be used with any device that may automatically switch them off and on frequently.

I have used X-10 devices to remotely switch them on/off but CFLs often have a strange low flicker, right after being turned off, which will often trigger the X-10 to turn the bulb back on. If you plug an unused low-volt power transformer(wall wart?) on the lamp side of the X-10 relay, it will absorb the transients and the CFL will stay off.

The 400w CMH is designed to be operated vertically, but as in all HIDs, they can be used horizontally with a reduction in lumens.

Zink

I've tried dimming a CFL, no joy. Some CFLs (small domestic units) are sold as dimmable, but I haven't tried this, I imagine they are only dimmable on certain dimmers. I can check if you really need to know this.

I assume you are planning on using one of the big high power CFLs, effectively just a four or six foot fluorescent bent in half? They will dim just about as well as the straight tube would, that is not well!

I do use a timer though, no problems there. I guess it depends on the timer and the ballast on the lamp. A good timer design should prevent feedback from the switched circuit. If my timer wasn't capable of turning off a CFL then I would take it back and get a different one. Do make sure the timer is rated comfortably for the load.

I'm sure you would take a timer back if you didn't know what was happening. The X10 system is a powerline-signalled remote control device system, conceived in the UK decades before CFL's became popular. It is the electronic ballast, not the lamp section, that causes the problem by sending some unusual signals right after turning them off. Most CFLs do this, but I wouldn't take the CFL back just because of that.

I know that the X10 was not the topic here, but those who have used this system for years might wonder what is going on when this happens. I had the X10's BEFORE the advent of today's newer lighting, as many others here also might. Since I happen to be able to hack the devices to do more that they were designed for, I have no problem with CFL's either. Of the 3 possible workarounds for the problem, the addition of an unused low-voltage power transformer on the lamp side of the X10 device is the simplest solution for the nontechnical person to achieve. Especially since there are an abundance of those little black boxes around. No need to throw out your venerable X10's just because you're not electronically savvy.

This forum is to help poor folks achieve their visions of greatness with less, and I shall help with that. Maybe next time I might show folks how to use an X10 to operate a large relay, which they can easily recycle(scavenge) from other devices, to turn those high amp HIDs off/on without running it through the X10. That may be a bit technical, though, for the timer-challenged to achieve.

And yes, do check the load. Consider that an HID may consume up to 20%(a bit high) more than the lamp rating, and is also an INDUCTIVE device, which can generate a some high voltage spikes on start/stop.

Zink (on a tangent)

Thanks guys....appreciate the response. Yes, I was looking at the higher wattages. I'll let ya kow how things turn out....

I wouldn't take the CFL back, I'd take the timer back :)

Folks, I have spent many hours searching for quality dimmable CFLs, and have finally found a type that WORKS. The type is "Cold Cathode" CFLs (I'll just say CCCFL). Ever since I discovered these at CFL Universe (link attached) I have been very happy with the results. They are TRULY dimmable, not the half-dimmable / flickery ones you get at Home Depot and the like that claim to be dimmable. They are on the side (e.g. $13 ~ $18 each), but they are rated at 25,000 hours of operation and, like I said, truly and smoothly dimmable over almost the entire range (I'd say 95 ~ 98%; some flicker slightly at very bottom of range). I figure they will eventually pay for themselves due to much lower energy consumption (especially when dimmed). I did have out-of-box failure on a bulb on a couple of different orders, but I emailed the company and they promptly shipped out replacements no questions asked. Give 'em a try and let's go green together!

Here is a link that might be useful: CFL Universe

A question - why would one even want to dim a bulb used for growing? If you don't need as many lumens, get smaller bulbs!

As for a timer, I've been using 105 watt CFL bulbs for three years and they all run off a cheap timer.

Mike