Just to prove they exist, here are some F18T8 cool whites. Don't look at the price unless you're sitting down with a stiff drink! 17W should be much easier to find, that is possibly the most common 24" tube now. Still likely to be twice the price of a 48" tube of similar quality! HD staff have no clue what they are talking about. 15W, 17W, or 18W will all run fine on your 18W ballast. The difference is well within the variation in ballast factors between different ballasts anyway, which means that some 15W ballasts will actually drive a tube harder than some 18W ballasts.

One way to turn your open IE off.... is to touch top of the display and drag it down to the bottom of the display. 2nd way would be to touch left side of screen and drag slightly to right to open the history... and then touch and drag IE out and down to the bottom of the display. /// One way to find Windows Updates would be to touch upper right side of screen and drag slightly to the left.. there you will open the Charms Bar and see the search icon. Search Updates and you'll see windows updates in the list. /// From that Charms Bar you will also see the gear for 'Settings' from that you can access the Power icon allowing you to restart or shutdown.

Well, seems I now have W8.1 on my subject Laptop. I made numerous requests to the MS Store and left my computer on overnight a couple times, nothing. Then suddenly this afternoon, about a hour ago I get a notice that MS wants to update to W8.1. a "restart" was needed. I click go ahead and forget about doing any work while that is going on. The "you can work applied only to the download which it seems was completed without any notice on my part. But, from there it takes at least 20 minutes for Update to do its work, including a second password code being required. I agreed that the "code" could be telephoned to me. After about a 5 minute wait I went back and requested the "code" be sent to my email address... I have another computer on-line to catch the email. Got the password/code there within the next two minutes. Some of the other "stuff" I am not yet altogether comfortable with, but what choice do I have: 1) The legal stuff seems to give MS lots of access to my computer 2) It appears W8.1 introduces "cloud" storage for those of us who have thus far gotten by just fine without it. This seems to be the purpose of the "Sky Drive" on the W8+ Set of tiles and it seems some of the operational OS stuff is backed up, but not sure I understand yet what else of "mine" is simply taken by MS and put on the "Sky Drive" and anywhere else pleases them. The update chanced the desktop boot up desktop from a scene of Seattle with an enlarged Space Needle to a colorful circular pattern, not better but I was not given a choice. The display on my Laptop seems brighter, maybe more HD, is that a possible effect of the W8.1 upgrade...right I didn't read the MS marketing stuff. Well for better or worse I now have W8.1 on my one and only W8 machine: still have one W7 and numerous XP only one of which is still active. Thank to all as I worked to get W8.1 upgrade on my qualified (free upgrade) machine.

If you want detailed advice about energy efficiency and building science, start at greenbuildingtalk.com. It's a good forum with many professionals chiming in.