I've been looking into the same thing.
AlienBees™ Technical Specifications[/b]]
<table width="405" cellpadding="0" cellspacing="0" border="1"]
<tbody>
<tr>
<td bgcolor="#87cefa" class="bee"]
<div align="center"]<span style="font-size: 14pt;"]<span style="font-family: Arial,Helvetica,Geneva,Swiss,SunSans-Regular;"]guide numbers </div>
</td>
<td bgcolor="#87cefa" class="bee"]<span style="font-family: Arial,Helvetica,Geneva,Swiss,SunSans-Regular;"] B400</td>
<td bgcolor="#87cefa" class="bee"]<span style="font-family: Arial,Helvetica,Geneva,Swiss,SunSans-Regular;"] B800</td>
<td bgcolor="#87cefa" class="bee"]<span style="font-family: Arial,Helvetica,Geneva,Swiss,SunSans-Regular;"] B1600</td>
</tr>
<tr>
<td bgcolor="#87cefa" class="bee"]
<div align="center"]<span style="font-family: Arial,Helvetica,Geneva,Swiss,SunSans-Regular;"]Standard 7-inch Reflector</div>
</td>
<td class="bee"]
<div align="center"]<span style="font-family: Arial,Helvetica,Geneva,Swiss,SunSans-Regular;"] #118</div>
</td>
<td bgcolor="#f0ffff" class="bee"]
<div align="center"]<span style="font-family: Arial,Helvetica,Geneva,Swiss,SunSans-Regular;"] #172</div>
</td>
<td class="bee"]
<div align="center"]<span style="font-family: Arial,Helvetica,Geneva,Swiss,SunSans-Regular;"]#236</div>
</td>
</tr>
<tr>
<td bgcolor="#87cefa" class="bee"]
<div align="center"]<span style="font-family: Arial,Helvetica,Geneva,Swiss,SunSans-Regular;"]11-inch Reflector</div>
</td>
<td class="bee"]
<div align="center"]<span style="font-family: Arial,Helvetica,Geneva,Swiss,SunSans-Regular;"]#220</div>
</td>
<td bgcolor="#f0ffff" class="bee"]
<div align="center"]<span style="font-family: Arial,Helvetica,Geneva,Swiss,SunSans-Regular;"] #320</div>
</td>
<td class="bee"]
<div align="center"]<span style="font-family: Arial,Helvetica,Geneva,Swiss,SunSans-Regular;"]#450</div>
</td>
</tr>
</tbody>
</table>
<span style="font-size: xx-small;"]We get a lot of questions asking, what is the "guide number" of your flash unit? This term is not wholly reliable because it relates more to the angle of the reflector than to the actual amount of light produced. For example, a flash unit with a given amount of light output will register a much higher guide number (f-stop at 10') if it has a narrow angle reflector (for telephoto lens) than if it has a wide angle reflector. But the actual amount of light is the same in both cases…it just covers more area with the wide angle reflector (at a lower guide number). In comparing flash units, the max GN of a flash unit is usually given for ISO 100 film. When it comes to choosing a flash unit, you have to be careful, as these measurements can be altered. It is common practice within the flash unit industry (for marketing reasons) to provide the max GN at the smallest coverage, as this will provide the longest focal length. Such a focused flash unit is more powerful, which produces a higher Guide Number, implying a more powerful output. Therefore, the max GNs of different flash units are usually not directly comparable. Studio flash units are designed to be used in many different configurations, with different accessories. The angle of coverage will be different in each case as will be the achieved guide number for a given amount of emitted light. As merely an indication of output, we publish the max guide numbers, noting that they are not true measurements of what you can do with our lights, as the real output will be determined by how you choose to modify the light.
<div style="CLEAR: both"]</div>
Click here ("http://www.alienbees.com/specs.html) to go to the AlienBees™ ("http://www.alienbees.com/)web site to see this in context.