David, thanks for your reply. Will the LED CR4 simply screw into my existing can, or does the housing need to be retrofitted?

If the existing housing is similar to the HI99CAT in depth, yes the CR4 will just screw into the E26 base socket.
The model number of the Home Depot CR4 is ECO4-575L.

Today I picked up an Ecosmart LED PAR20 40W equivalent at HD for $20. I'm waiting for night to fall to see if I get any more brightness out of it compared to the others. With this I will have tried incandescent, halogen, CFL and LED.

I saw the CR4 ECO4-575L when I was at HD. Everyone on this board and others says they're a snap to install in 4" receptacles. I have no electrical chops so if I go that route (which is looking more likely), I'll need some help with retrofitting.

Not all LEDs lamps are created equal.

The CR4 is really easy to fit (assuming a standard depth 4" edison base recessed can). - just screw in the pigtail, make sure the 3 prongs are fully extended and push in the module, giving it a slight clockwise twist.

The clockwise twist will ensure that the 3 prongs are fully extended and will grip the can properly.

No electrical know how is required other than the standard safety precaution of not installing the lamp when the circuit is hot/ on.

The procedure is almost identical for the CR4, except that the CR4 has an attached pigtail unlike the CR6.

Here is a link that might be useful: CR6 install

David, thanks for the vote of confidence. Electricity is a mystery to me and I have a healthy respect for it. :)

What happens to the existing can? Does it have to come out first, i.e., is the CR4 replacing the whole unit, not just the light itself? I found some videos on Youtube and they took out the can (receptacle + trim). The guy was futzing around with little doo-dads up there.

Am I making this harder than it really is?

One of my 4" cans with 45W Philips incandescent:

The existing can remains in place.

Why so many steps for the CR6/ LR6 (Edison base)
Most of the videos are about the CR6. For a standard can, there is an adjustable plate to which the E26 socket is attached. This plate is there to allow the use of various bulbs - short /long neck bulbs

The socket needs to be removed from the plate and left dangling.

For the CR4,
1. Unscrew the bulb.
2. Remove the existing trim. If your can is similar to the HI99CAT, there will not be an adjustable plate. This is most likely the case.
3. Make sure the 3 tabs are fully extended.
4. Screw in the E26 end of the pigtail.
5. Push the lamp into the existing can and give it a slight clockwise twist at the end.

David, you are most kind to take the trouble to explain this to me. I realize I have been saying can and trim interchangeably. I know they're different. It sounds like the existing trim just pops out? Is the end of the pigtail like the end of a regular bulb? If something goes awry, would I remove the CR4 by turning counter-clockwise? I'm gonna try this!!!

Yes to all.

The existing trim on your recessed can will be attached to the can by springs. This needs to be removed as the CR4 comes with the trim attached.

The end of the pigtail is the standard E26 connector.

If you need to remove the CR4, turn it counter-clockwise while pulling it out.

Picture says a thousand words.... this is the ECO4-575L (CR4) with the included, built-in trim ring and pigtail connector:

I'm back yet again. :) Before buying the ECO4-575L, I decided to remove the existing trim. It seems to be in there pretty good and doesn't want to budge. I tried to unscrew it. Nothing. Should it just pop out? I get some slight downward movement, but if it's got a mechanism to hold it in place, I don't want to bust it out and damage it.

The trim is held in place using springs which need to be unclipped/ un-hooked. Pull down slightly on the trim to find the springs.

Okay, I was able to remove the trim from a different can. It seems to have been held in by 4 springs around the sides. I can see that it's meant to go in easily, but don't see any way to get it out with risking damage to the springs or ceiling texture. Any ideas how these guys are supposed to be removed correctly:

The springs need to be forced inwards simultaneously. Probably a circular clamp could be used like a strong nylon string tied around the springs, worked upwards and tightened while you pull the trim down gently.

Yippee, success!!! I'll have to wait until nightfall to see what the light really looks like, but I can see it is much brighter than the 45W in the other cans.

The hardest part was screwing in the end of the pigtail. It was tricky holding on to the main unit with one hand while getting inside the small housing and getting sufficient purchase to engage the screw threads. Good thing I have small hands.

The trim is a little whiter than my other cans. If this is as good as I think it will be, I'll gradually swap out the others, and it'll all be good.

Thank you all for your kind and patient help. Without your encouragement, I wouldn't have dreamed I could do something like this.

Great news!

And all five of your LED lights put together will use less electricity than the one old 6" light did.

lee676, I know! How crazy is that? Of course, they will end up costing me $250 but if I live long enough, I'll recoup the cost.

And oh my, it is so much brighter than the regular cans. A very nice color and broad, even spread of light.

The LEDs will probably outlast all of us....

But replacing halogen PAR bulbs when they burn out adds up oveer time as well. I try to catch people before they install their recessed cans and tell them about the LED modules, since they'll save about $12 on each trim baffle they won't need.