There is so much more to light and its impact on our health and well-being. But I really like to the way you connected it to our living environment. We can all use more light. If we can agree that at the moment we are not getting the correct amount of light indoors, then we must do two things. One, spend more times outdoors especially early during the day, if we can. Two, redesign our living environment with a focus on health and well-being. We are part of the natural ecosystem and our built environment needs to embrace and reflect that. We need convertible spaces, soft edges, and mid-scapes.
This is a very interesting post and I need to read some of your references. At the moment I am working on a presentation for the Westford Building Science Symposium this summer called Fundamentals of Solar Energy. This has me looking at the solar spectrum, the effect on the spectrum with different glazing choices, and the spectra offered by artificial light sources.
Low-emissivity coatings vary a lot in terms of their transmissivity vs. wavelength. What I will call 'solar low-e' coatings such as hard-coat products such as Cardinal i89 (I'll use Cardinal products as they are the ones I know best) or soft coat 180 don't suppress near IR much compared to clear glass. So they let in more heat. That's desirable if a building is well oriented (south in my part of the world, central New England) and not over-glazed. The introduction of heat-rejecting low-e coatings achieve their performance by reducing VLT some, but near IR a lot. In the Cardinal product line-up, Low-e2-272 has become a pretty standard product in most high quality residential windows being sold into our market, and low-e3-366 has appeared on submittals for a number of my residential projects in recent years. This has allowed designers to use more glass in non-optimum orientations.
Here are center-of-glass values for double glazing with the three low-e coatings:
clear ext, 180 int - 0.788 VLT, 0.676 SHGC
272 ext, clear int - 0.716 VLT, 0.413 SHGC
366 ext, clear int - 0.645 VLT, 0.272 SHGC
The Solar Heat Gain Coefficient is a measure of total energy transmitted (by all processes, so includes conduction and re-radiation, etc., not just transmission). The selective low-e products attempt to suppress VLT minimally while cutting as much near IR as possible. Cardinal's data for 366 shows close to zero transmission in the near IR.
So, if these health effects are real, then it seems that proper orientation and appropriate glazing amounts become even more helpful, so as to use solar low-e instead of heat rejecting low-e. I chose triple glazing in the gut renovation of our house in 2013. There are five large fixed windows along the south side totalling about 90 sf (8.4 m2) of glazing, and the lay-up from out to in is low iron clear/180/180. VLT is 0.698 and SHGC is 0.618. That space is where we spend most of our time (kitchen-dining-living, one room). It's pretty bright!
Zooming out from windows, it feels to me that getting outdoors is most important. My own commitment to myself is to spend two hours minimum outside daily. I do wear sunglasses during much of that time, so perhaps I'm not getting the light benefits, but I'm on a bicycle pretty much daily and need eye protection from physical damage.
Marc, what glazing did you use for the rest of your windows? I used the same Low iron / 180/ 180 configuration for a house build in 2010. All of the sealed units failed and had to be replaced within 12 years. Most within 10 years. Cardinal warrantied the product for 10 years.
This is a very interesting comment, thank you very much!
The five south-facing fixed windows are 63"x43" and are glazed as described above. The renovation was done in 2013. One failed in 2016, another in 2022. Alpen replaced the first one. The second failure prompted Alpen to send four new units, so that all five would be replacement units, even though three of the original units hadn't failed. The window techs broke one unit taking it out, and I have the other two stored as potential backup replacements. These fixed units are all 3/16" lites.
The other windows in the house are operable casements and awnings, and are clear-180-180. no low iron exterior. They are also tempered (the fixed are annealed) and are 1/8" lites. None have failed. Only two also face south.
I chose three lites of glass instead of using a Heat Mirror film because in a couple of projects years ago we saw some issues with the film wrinkling pretty much when delivered, and I thought that all glass units would be more robust. (This is somewhat ironic - I was a very early adopter of Heat Mirror, framing HM units into fixed openings in New Hampshire houses before HM became available in commercially available windows - I knew some people associated with the company that made the film).
I have since heard from some people that putting a low-e coating on the middle lite is risky because the coated glass absorbs more heat than clear glass, and this can cause seal failure. Your experience which is similar to mine is perhaps an indication that this may be the cause of the failure, even though the 180 is a high transmission coating with relatively low absorption. I'm still somewhat confused as to why the conditions the windows you and I have experience with would result in higher temperatures in the lites than, for example, a double glazed unit in Arizona facing southwest with low-e 366 on the exterior lite, and 120F outdoor temperatures, and a shade pulled inside of the window.
Thanks for your input. Feel free to call me if you want to discuss further. So far, there are not tariffs on calls from Canada to the US.
Interesting piece. I found myself thinking about Norwegian design and practice. When travelling in fall and winter, the hotels would have candles on the table at breakfast. I was also struck by the number of atriums and bright yellow restaurants. I assumed that all were designed to reflect light in the dark falls and winters. Living in a city with a hefty number of overcast days, I found myself turning on bright lights to get moving and the closing curtains at night to block out the halogen street lights. But it sounds like this all may need tweaking.
Greatly informative post, Lloyd. Thank you.
There is so much more to light and its impact on our health and well-being. But I really like to the way you connected it to our living environment. We can all use more light. If we can agree that at the moment we are not getting the correct amount of light indoors, then we must do two things. One, spend more times outdoors especially early during the day, if we can. Two, redesign our living environment with a focus on health and well-being. We are part of the natural ecosystem and our built environment needs to embrace and reflect that. We need convertible spaces, soft edges, and mid-scapes.
It was your earlier provocative comment that got me into this rabbit hole, thank you for that.
This is a very interesting post and I need to read some of your references. At the moment I am working on a presentation for the Westford Building Science Symposium this summer called Fundamentals of Solar Energy. This has me looking at the solar spectrum, the effect on the spectrum with different glazing choices, and the spectra offered by artificial light sources.
Low-emissivity coatings vary a lot in terms of their transmissivity vs. wavelength. What I will call 'solar low-e' coatings such as hard-coat products such as Cardinal i89 (I'll use Cardinal products as they are the ones I know best) or soft coat 180 don't suppress near IR much compared to clear glass. So they let in more heat. That's desirable if a building is well oriented (south in my part of the world, central New England) and not over-glazed. The introduction of heat-rejecting low-e coatings achieve their performance by reducing VLT some, but near IR a lot. In the Cardinal product line-up, Low-e2-272 has become a pretty standard product in most high quality residential windows being sold into our market, and low-e3-366 has appeared on submittals for a number of my residential projects in recent years. This has allowed designers to use more glass in non-optimum orientations.
Here are center-of-glass values for double glazing with the three low-e coatings:
clear ext, 180 int - 0.788 VLT, 0.676 SHGC
272 ext, clear int - 0.716 VLT, 0.413 SHGC
366 ext, clear int - 0.645 VLT, 0.272 SHGC
The Solar Heat Gain Coefficient is a measure of total energy transmitted (by all processes, so includes conduction and re-radiation, etc., not just transmission). The selective low-e products attempt to suppress VLT minimally while cutting as much near IR as possible. Cardinal's data for 366 shows close to zero transmission in the near IR.
So, if these health effects are real, then it seems that proper orientation and appropriate glazing amounts become even more helpful, so as to use solar low-e instead of heat rejecting low-e. I chose triple glazing in the gut renovation of our house in 2013. There are five large fixed windows along the south side totalling about 90 sf (8.4 m2) of glazing, and the lay-up from out to in is low iron clear/180/180. VLT is 0.698 and SHGC is 0.618. That space is where we spend most of our time (kitchen-dining-living, one room). It's pretty bright!
Zooming out from windows, it feels to me that getting outdoors is most important. My own commitment to myself is to spend two hours minimum outside daily. I do wear sunglasses during much of that time, so perhaps I'm not getting the light benefits, but I'm on a bicycle pretty much daily and need eye protection from physical damage.
Thank you for this post.
That’s a key message of the books- get outside, especially in the morning. Thanks for the comment!
Exactly! A wonderfully low-tech solution to a genuine problem that has additional benefits to mental and physical health.
Marc, what glazing did you use for the rest of your windows? I used the same Low iron / 180/ 180 configuration for a house build in 2010. All of the sealed units failed and had to be replaced within 12 years. Most within 10 years. Cardinal warrantied the product for 10 years.
This is a very interesting comment, thank you very much!
The five south-facing fixed windows are 63"x43" and are glazed as described above. The renovation was done in 2013. One failed in 2016, another in 2022. Alpen replaced the first one. The second failure prompted Alpen to send four new units, so that all five would be replacement units, even though three of the original units hadn't failed. The window techs broke one unit taking it out, and I have the other two stored as potential backup replacements. These fixed units are all 3/16" lites.
The other windows in the house are operable casements and awnings, and are clear-180-180. no low iron exterior. They are also tempered (the fixed are annealed) and are 1/8" lites. None have failed. Only two also face south.
I chose three lites of glass instead of using a Heat Mirror film because in a couple of projects years ago we saw some issues with the film wrinkling pretty much when delivered, and I thought that all glass units would be more robust. (This is somewhat ironic - I was a very early adopter of Heat Mirror, framing HM units into fixed openings in New Hampshire houses before HM became available in commercially available windows - I knew some people associated with the company that made the film).
I have since heard from some people that putting a low-e coating on the middle lite is risky because the coated glass absorbs more heat than clear glass, and this can cause seal failure. Your experience which is similar to mine is perhaps an indication that this may be the cause of the failure, even though the 180 is a high transmission coating with relatively low absorption. I'm still somewhat confused as to why the conditions the windows you and I have experience with would result in higher temperatures in the lites than, for example, a double glazed unit in Arizona facing southwest with low-e 366 on the exterior lite, and 120F outdoor temperatures, and a shade pulled inside of the window.
Thanks for your input. Feel free to call me if you want to discuss further. So far, there are not tariffs on calls from Canada to the US.
Interesting piece. I found myself thinking about Norwegian design and practice. When travelling in fall and winter, the hotels would have candles on the table at breakfast. I was also struck by the number of atriums and bright yellow restaurants. I assumed that all were designed to reflect light in the dark falls and winters. Living in a city with a hefty number of overcast days, I found myself turning on bright lights to get moving and the closing curtains at night to block out the halogen street lights. But it sounds like this all may need tweaking.
Very interesting food for thought. Maybe we like to over glaze modern buildings because subconsciously we know we are not outdoors often enough.