You need to go do some research on the Lighting forum...
To start, here is a thread I clipped with some basics about LED and recessed lighting.

For what it is worth, I have recessed, ICAT lights, with LED (cree) lights. Love them!

Here is a link that might be useful: kitchen lighting answers from lighting forum

IC stands for insulation contact, which means the housing of the fixture can come in contact with insulation. Non-IC, means that you need to keep insulation away from the, typically about 3". Air tight is just that, the fixture is sealed to prevent air movement through the fixture which can save on energy costs.

IC is not nearly as important if you have an LED fixture.

They are far lower power than incandescent bulbs.

If you use an LED fixture you are likely tied to the OEMs hardware.

This post was edited by brickeyee on Fri, Feb 15, 13 at 10:19

it isn't the heat of the bulb, or even bulb type
that is the reason for chosing ICAT over IC.

you want a recessed light that doesn't allow
attic temps, dust & insulation particles into the
living space.IC lights have holes in the housing
with insulation installed next to housing.
ICAT no holes in housing.

so ICAT is the choice.
once the ICAT lights are installed, the next
air leakage area is the cut in the sheetrock
around the recessed light.
once trim kits are installed this oversized
cut is hiden, but should be sealed prior
to trim kit.

I use hardcast brand #1402 mastic tape
to seal the housing to the sheetrock
within the area covered by the trim kit.
some caulk, but caulk to sheetrock cut
isn't the best method.
you can't seal to sheetrock dust, and if
you use more caulk, once it dries it
shrinks so you still have the gap.

using mastic tape is the best long lasting
way I've found to seal these and other
oversized cuts in sheetrock.
including..bath fan, and supply boxes
for hvac.

I find these leakage sites from the most
extreme temps in attic directly into the
living space to be very worthwhile sealing.

best of luck.

Kirkhall, thank you very much for the information and the link. What specific model did you buy? Would you please give me a link if possible? Is 2700K almost the same as incandescent light or would 3000K be more appropriate for me if I feel the incandescent light is too yellow. Of course, I don't want daylight color which is too cold in the evening.

Mike, thank you very much for the detailed explanation. I think air tight is important.

Brickeyee, thank you very much for the additional information, which is very helpful.

energy_rater_la, thank you so much for the very helpful information. I'll buy the hardcast brand #1402 mastic tape and ask the general contractor to seal the housing to the sheetrock with it. I've never heard of ICAT (air tight?), only heard of IC and air tight. What's a good brand of recessed light that is ICAT?

Really appreciate all your kind help.

ICAT is insulation contact air tight.
juno is a common brand in my area.
just make sure they are ICAT and not just IC.

as for expecting gc to do this type of air sealing..
good luck.
better you diy or hire someone to seal these
areas, recessed lights, bath vent fans, stove
vent & hvac supply boxes.
if trades people would seal the holes they
make it would eliminate the need for this.
but itrw..they don't.

that is why people like me are hired to oversee
air sealing details.

here is an example of how to seal hvac supply
boxes before supply registers are installed.

best of luck.

ICAT and sealed are not always perfectly tied.

what?

energy_rater_la, thank you very much for the information and the picture.

I saw some recessed LED trim was marked as IC rated and air tight. Halo recessed cans are also marked as IC rated and air tight. Do I need to choose both recessed LED trim and recessed can ICAT or the can's ICAT is enough and whether the trim is ICAT does not matter?

Thank you very much for your help.

air tight trim is a joke in my opinion.I base this on
having tested for air leakage with a blower
door while sealing these lights & trims.

the foam rubber gasket does little to stop the
air leakage from exiting the trim.

the best way I've found is to use the hardcast 1402
mastic tape to seal housing to the sheetrock.
similar to how supply box is sealed in pic of
previous posting. tape goes into edge of housing
and overlaps to sheetrock. allow 1'2" overlap
as trim will cover the tape.

this with the ICAT recessed light will stop as much
of the air leakage as possible. there will still be
a small amount of leakage, but not enough to
be of concern.

note this when you look at the recessed lights again:
Halo's insulation contact air tight lights have two
things that identify them.
no holes in housing
and a orange sticker inside the can that says
it is air tight. orange sticker, not red.

the red sticker says air tight when used with the
following trim kits. deceptive lableling IMO.

reading the small print inside IC cans the
trim kits include, insert/baffle to fit inside the can
to address holes in housing (@$14 each)
and air tight trim kit, not sure of cost.

as the insert/baffle would be needed at every
recessed light, buying ICAT makes better
economical sense. installing the baffles
is a pita. so add labor for that to cost.

buy ICAT, use mastic tape in place of 'air
tight' trim. if you are putting IC cans outside
under porches patio, unconditioned space
this is what happens.
as the install of recessed lights is ongoing,
the electrician mixes up the boxes.
some inside are ICAT, some IC. same outside.

make it easy on everyone and buy all ICAT.
wasps like IC, but not so much ICAT, less
air movement.
the cost per contractor case between the
two is minimal when you compare to retrofitting
each IC to air tight.

best of luck.

energy_rater_la, thank you very much for the information.

I went to Home Depot and did not see the hardcast 1402
mastic tape, but they have Nashua Premium Foil Tape.
Is it fine to buy the Home Depot's Nashua Premium Foil Tape?

I only found the hardcast tape you mentioned in amazon as shown in the link below. Is it the right one?

Here is a link that might be useful: Hardcast Rolled Mastic Duct Sealants Foils 3'' X100

You want a mastic tape, not just a foil tape.

I bought Lowe's brand (Utilitech) ICAT new construction 4" housings for my kitchen, and then the 4" integrated LED/trims from HD--"Ecosmart" brand. I have the usual edison base housing (no requirements for gu24, thankfully) so at my HD, I could get the Edison base LED Ecolights, not the GU24 ones (linked below). Not sure what your state requires...

One note on the integrated LED/trims like this Ecosmart brand--The trims are not wide. So, don't let your GC/electrician make too large a hole in your drywall, or you may have trouble covering it up all the way. And, using the mastic tape may be difficult to cover with the trims as well. You'll only want to extend it slightly over the ceiling drywall. Keep it mostly in the can (since most are 2" width).

Here is a link that might be useful: Ecosmart LED like what I got.

Kirkhall, thank you so much for the information. I searched online and found Home Depot sells Scotch mastic tape 1"x10'. Is it still better to order online the Hardcast one from amazon (is the link in my last post the right one?)?

Only after reading your response did I realize that there are two base choices, GU24 and Edison. I did not notice there is base difference for each LED/trim when I visited the HD and Lowe's. I am living in California, and I need the GU24 base in order to be in compliance with Title 24.

Really appreciate your help.

This post was edited by janesylvia on Mon, Feb 18, 13 at 17:07

http://www.ebay.com/itm/HVAC-Hardcast-AFG-1402-Rolled-Mastic-Duct-Sealant-Tape-3-x100-Topmost-Quality-/321032199173?pt=LH_DefaultDomain_0amp;var=&hash=item4abf029c05

sorry for the long link.
the 1" tape isn't wide enough.
the other link isn't the right product.
having used most brands of mastic tape
Hardcast 1402 is the best for multiple areas
of seal. this material will adhere to sheetrock
wood foil metal and many surfaces as long
as clean & dry.

here is the link to the hvac supply house I use.
http://www.solarsupply.us/id6.html

best of luck.

Thank you so much, energy_rater_la.

You said the one sold on amazon is not right? I saw it's Hardcast, Mfg. #: AFG-1402-3; Size: 3" x 100'. I already ordered it yesterday afternoon. If it's not right, I can still cancel it now and will order it on ebay.

Thank you so much for your help.

Here is a link that might be useful: Rolled Mastic Duct Sealants Foils 3'' X100

This post was edited by janesylvia on Tue, Feb 19, 13 at 15:06