Nightlight Pad Temperature Rating

I own the Nlight and Tlight. As far as I know, insulation contributes an R-value which is then added in to the other layers of your sleep system (ground sheet, tent floor, foam mat, inflatable mat, sleeping bag, bivy sack, tent dead air space, tent wall, etc..)
Therefore it would be difficult to estimate at what ground or air temperature you would be comfortable using a Nightlight without knowing your BMR(search the forums) and all components of your sleep system.
Personally, I'm good down to 0'C with a 1" inflatable foam pad, and the Thinlight inside a single wall tent; using a 1 lb down bag and a 1" loft jacket. But I sleep warm. Sorry I could not be more help. Maybe if you describe your sleep system…

Brett, my BMR is 1526 kcals/day (http://home.fuse.net/clymer/bmi/) and my current sleep system consists of
– 2mm painters plastic ground cloth
– GG Nightlight 3/4 length
– WM Ultralite (20F) bag
– SMD Gatewood Cape

Supplemental sleep insulation
– Patagonia long underwear bottom (light weight)
– Sekri zip tee long underwear top
– merino socks
– OR Ion wind jacket
– Micropuff pull over
– Polar Buff hat
– Montbell fleece gloves
– 2 bagel sacks (hand/feet protection)
– GG Mariposa+ with Sitlight pad (currently pillow)

I am not worried so much about loft over the top of me, but want to make sure I have enough insulation below me.

Edit: I also carry a dentist mask to help with respiratory heat loss.

I would say that if you are unsure that it would be better to play it safe and bring along the ThinLight. Its cheap enough and light enough that it won't be a huge inconvenience plus you could try without it one night to see how much of a difference it makes.
I have a NightLight Torso and 1/8" ThinLight and used them both this past weekend. It was about 46*F when we woke up and I could definitely tell that my feet were hanging off the ThinLight, as they were considerably colder. I can't say for sure whether my torso, which had the combo of TL and NL, was warmer than my legs with just the TL though.
Where's Richard, with all of his hard and fast numbers regarding heat, clo, R-value, etc, when you need him? :)

Adam

Should add that GG Thinlights come in 3 thicknesses: 1/8 (R.45), 1/4 (R.90) and 3/8 (R1.42). GG Nightlight is R2.27.

Steve, you have a great setup.. I don't see any full length ground insulation on your list so I would add the 1/8" thinlight. Last winter I slept on solid ice and could not detect any cold feeling when testing only the Thinlight. As you probably know, the foam insulation is critical under your body because any compressible insulation is flat and not very useful. My hiking companion slept on an inflatable mattress (no foam), and lost heat down to the ground.

I don't see any full length ground insulation on your list

That is because I am a side sleeper and have my entire body scrunched on the Nightlight (59"), with my pack and Sitlight pad as a pillow.

Steve,
I have used the Nightlight/Thinlight combo down to the mid 30's without any discomfort, but I am sceptical that you could take it down into the teens(I have a BMR of 1350, although I'm not sure what that has to do with this problem; it is a function of weight*calorie constant/kg body weight, as I understand how it is calculated). One sure way to find out is to try it and see. It would also seem to me that as you graduate to thicker Thinlights you will, at some point, run into bulk problems; This may, or may not, matter depending on your pack, hiking style(trail, bushwhacking, scrambling, etc), but perhaps you might consider an inflatable pad/Thinlight combo at some point in that progression. In my case I rapidly reached that point, since a substantial portion of my trips are at least partially offtrail/bushwhack/scramble terrain where bulk, especially lashed to the outside of my pack is not a good option; For those trips I use a heavier(~5 oz) Montbell/Thinlight combo which has worked, so far, down into the mid 20's. I still use the Nightlight/Thinlight combo for trail hikes, however. One last thought: I have glued a ~8" section of an old Thinlight pad over the foot end of my working Thinlight(1/8" in both cases, to provide extra warmth/padding for my heels, which tend to compress the 1/8" foam and cause both discomfort and coldness for my heels, especially when I'm sleeping on my back. Would you please post back the results of your problem solving? This would be of interest to a lot of us, I'd bet.

Steve, like Tom said, I am also interested in your results; I just could not get comfortable on the Night/Thin light combo. I believe it would be insultative enough, but not 'cushy' enough for me. More power to you for being able to go that light..

This has been a really interesting thread for me to follow as I'm in the process of putting togethere a lightweight sleep system. Thanks for all the info and hints.

However, I'm curious what you guys do when it gets really cold outside in the winter? I assume the Thinlight/Nightlight combo will only take you down to the mid 20s. What about colder weather?

According to the most recent gear list I could find for Ryan’s SUL Winter Challenge he took two foam pads:

3.7 Gossamer Gear NightLight Torso (R2.27)
5.7 Gossamer Gear Thinlight 3/8 19.5 x 59 (R1.42)
====
9.4 oz

Edit:
And from an email I received yesterday from Grant at Gossamer Gear, “I asked Ed Viesturs what he uses when climbing and sleeping on snow/ice and he said always foam.”

Personally, I go heavy. I use an Exped downmat 9 which has an R value of 8.0 and is rated to -36. I've only had it down to -10 so far but I stayed warm and I'm a cold sleeper.