In my particular case, I've been using the Sylvania brand CFLs that have the spiral elements, the ones that advertise that they put out 5 Watts or 13 Watts, but claim to deliver more "Light" than that, I suppose more light with respect to lumens than the wattage ratings would otherwise be anticipated to deliver from a conventional/incandescent bulb.
Here are the links to the exact ones I'm using via Lowes.com regarding the 5-Watt and the 13-Watt Versions:
Here is the link on Lowes.com to the 5 Watt ($4.57 each):
Here is the link on Lowes.com to the 13 Watt ($6.98 each):
Sylvania also manufactures a 23 Watt version, and here is the link to that one as well, but I haven't used it because I figured that the lumens rating is too high for my tanks, which are small, only 10 gallon, 20 gallon, and 28 gallon (Cube).
The 23-Watt ($10.61 each) might be applicable too your request for a listing. I'm not advocating the use of CFLs particularly for use in aquarium light fixtures, but I do like that they're at least in the light color range that has relevance to aquarium lighting, versus the incandescents. I am curious to know if the CFLs can be used to reliabily calibrate the CEPs, and whether those readings can be relied upon to design other more sophisticated fixtures to PAR.
I recommend testing these models above because they are commonly available, from a well known manufacturer, under or about at the $10.00 amount Hoppy mentioned depending on size, and other forum members can easily obtain them throughout the entire country.
The other thing is they have a very small footprint, and I've been able to incorporate them into fixtures very easily. But, I have to admit, I haven't tried some of the other brands that might be out there. But, these in particular do burn cool, and can be easily incorporated into a home-made fixture. I'm sure there are much more sophisticated fixtures out there that are being built, ones that are really far superior than just a couple of CFLs. But, if we are trying to establish PAR for calibration of a CEP, and that PAR number from the CFLs can be established to be consistent between other types of bulbs and fixtures, using a commercially produced PAR meter, then we have a very convenient way of getting "close" with respect to calibration of the CEP without having to have a commercially produced PAR meter in our possession, or having to send our CEPs off to those members that might have a commercially produced PAR meter.
In the interest of being totally thorough, it will be necessary to test between several of the same model CFLs to establish a consistency level between CFL bulbs of the same model, but also between Lot Numbers, in order to establish a consistency expectation between CFLs of the same brand. And, to be really enterprising, perhaps comparing CFL PAR using a high quality commerically produced PAR meter to other types of light emitters.
We'll probably have to factor-in some kind of (+) or (-) statistcal deviation. But, I am hopeful the CFLs are relatively consistent between lot numbers, etc...and that the PAR readings from the CFLs are consistent with other types of emitters. If so, then theoretcially we could be relatively confident that we'll be able to calibrate our CEPs based on particular models of CFLs that have been tested for consistency, provided we use the same testing methodology by which Hoppy's testing process is conducted. And, of course, there is also the inconvenience of having to re-test when new designs come on the market, which is bound to happen.
I would also suggest that brand new bulbs be used to calibrate at all times, unless we can somehow forecast when the consistency in the bulb's life begins to drop off. If we can establish a length of hours that the bulb's performance is on "PAR," no pun intended, then we could conceivably save bulbs year after year for calibration purposes. But, even if we have to buy a new bulb each year, costing $5.00-$10.00, it's not particularly expensive to know that our CEPs are on PAR. But, having to buy a new bulb year after year, when there is a high likelihood that new models will emerge on the market that are untested, makes saving the bulbs for many years of use much more attractive.
I think it would be very interesting to see what the deviation is between different brands, such as Hoppy's GE, versus the Sylvanias I mentioned. It would really be quite a revelation if PAR readings are also consistent between various brands and lot numbers of CFLs. If that turns out the be the case, then the likelihood of new models throwing a wrench into past testing is significantly reduced.
This only works if those who are making a PAR meter have access to one of the bulbs used, and at a price that is far less than a good PAR meter. If that bulb costs $5 I think the idea works well. It it costs $15 I suspect that would discourage anyone from using this method.
I know that CFL bulbs, with a color temperature in the range of 6500K, will work for either an Apogee meter or a DIY PAR meter made similar to what I was making or what mistergreen makes. I'm not yet convinced that an incandescent bulb will do it, even though it works fine for re-checking your PAR meter once it is adjusted to read correctly. If there is a problem with that use it is the probable very low PAR reading you would get if you used it like I show here. At low readings there is a big inherent error just from the inability to read enough significant numbers.
What is a widely available CFL bulb, 6500K, that costs under $10 per bulb?