The criteria you should use for deciding between closed and open shape CFL is the bulb’s application. Are you going to be using it in an enclosed fixture or in a partially exposed application like in certain wall sconces? For enclosed fixtures, most people go with open CFLs for two predominant reasons. The first is that open CFLs, such as mini-twists are often less expensive and less appealing to look at than closed bulbs, so people try to use them wherever they can get away with it. Furthermore, closed CFLs are often enclosed in an additional frosted glass envelope, further diffusing the light. Enclosed fixtures often come with frosted plastic or glass diffusers, therefore by using an A-shape CFL, or other such closed CFL, in an enclosed fixture you could be softening the light excessively or simply using redundant diffusers and wasting money. Put simply, my rule of thumb is that for closed fixtures use open CFLs, and for open fixtures use closed CFLs. This should give you the light bulb and light you want.
When it comes to choosing between the different open CFL bulbs, you’ll again, want to take application into consideration. For lamps with shades, you’ll likely want to choose an open CFL with a smaller, more slender profile, such as a quad or triple tube bulb or a mini-twist. For larger fixtures, twist bulbs are a good choice. Similar considerations should be made when choosing among closed CFLs. Globe and candelabra CFLs are typically used in more decorative or specialty applications like bathroom lighting or wall sconces, where the shape of the bulb itself is important. A-shape bulbs are good in many applications. Don’t forget about closed R (reflector) or BR (bulge reflector) bulbs either, they are typically used in recessed applications or ceiling fan fixtures. Hopefully this guide has been helpful and will assist you in navigating the numerous CFL shapes available.
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