The Call of the Open Sidewalk

We had a wet spring and as a result my bedroom window looked like this;

It and some of my other windows of that type had looked like that in the past but this seemed a bit extreme. Some hunting around on the web revealed that people were sometimes managing to dry out multipane windows by drilling holes in them. Most were making 2 holes. I thought it might be interesting to just make one hole and see the results.

The thinking here is that I live in a cold and dry climate that has wide temperature swings. The water vapour might get pumped out by the trapped air expanding and contracting over each day-cycle. After all, that is likely how the water got in there in the first place.

The window is triple-pane and the fogged bit was of course on the other side from the drier environment outside. This meant drilling through two panes. I used this;

I would not recommend this tool for this application. It grabbed badly when clearing the hole on the outside pane. I did take reasonable precautions but this was still a bit scary with all that breakable heavy glass above the work area. There is some potential for serious injury with this activity. Something like a small diamond core drill would of been better as the hole can be made quite small. Using such a large tool wasted much time.

I used the felt like material from an old floppy disk as the filter. What is needed is something to keep small insects out that will not rot. I used a piece of a plastic pipe end cap as the rain cover. I used clear RTV sealant to hold everything to the window after cleaning the surfaces with alcohol.

I first put a thin coating of sealant on the edges of the filter. Using the point of a knife I positioned it over the hole. The rain cover then had a thin layer of sealant applied before it was placed on the window. A bit of duct tape held it in place while the sealant dried. Some glass dust ended up between the window panes. I wasted some time with a tube trying to vacuum the dust out. The dust fell to the bottom after the static electricity discharged.

The window took about a month to clear. I was left with very small water droplets that were mostly invisible in the summer. They froze in the winter and are a bit obvious now at 4 months into the experiment;

I am happy with the result and have no plan to add a second vent. If I do this again with another window I will put the vent at the top of the window in the centre. This would be better because;

• The vent would be better shielded from rain by the eave and window frame.
• The vent would be out of the reach of curious people.
• Drilling the vent would be safer as the glass would be below the work area.
• The window would defog from the centre top which might look nicer.

posted at: 13:52 | path: /house | permanent link to this entry | Comments (0)

I seem to be stuck on the low level lighting thing. An advantage to not working is not having anyone to tell me to get back to work...

Here is an approachable introduction to modern colour vision theory. It helped me a lot. The rest of the site (watercolours) is a bit too technical for me but I think I now know what to expect when I mix single colour LEDs.

For my bathroom night light I now think that just green and red LEDs would of worked fairly well. I could of balanced them to give some sort of yellow. A problem would occur if the colour was exactly the same as the perceived light colour. It would not be visible against white. The 3rd colour in between removes that ambiguity. That is assuming that the green and red LEDs do not balance out to the in between colour. The apparently excessively bright green LED is thus a feature as it moves the balance point well away from the yellow LED wavelength.

Another possible problem with just using green and red (or blue and red) is that you would end up with more green light. Green (and blue) can blind night vision when not used in moderation. I now think of my bathroom night light as primarily yellow with a bit of some other wavelengths thown in to allow some colour discrimination.

posted at: 17:13 | path: /ledlight | permanent link to this entry | Comments (0)

Some wisdom came out of my night light projects. I'll share that here.

Are light emitting diodes ready for prime time residential lighting? That question is surprisingly controversial. I am not really sure myself about the answer to the general question. I am sure that for low level lighting LEDs entirely rule.

Up to this point in the history of the world there has not been a practical and efficient way to make a small amount of light for a long time. Incandescents are particularly bad for efficiency and life. Electroluminescent were the closest thing pre-LED era but they are an area emitter and are thus hard to shade effectively. They also need high voltage wiring.

The result of this is that the system of vision intended to allow people to function at night is not really used by most people. People can see at levels down to 0.01 lux. Typical residential living spaces are lit to levels between 50 to 100 lux. That is as much as 4 orders of magnitude more than the absolute minimum required.

It may be that we have hit a technological threshold. If low level lighting is more practical then perhaps it will become more common. It is interesting to consider how a hypothetical low level lighting enthusiast would arrange the lighting in a house.

Let us first invent a specification. All living areas should be lit to the level of moonlight on a clear night. One source claims this is .3-1 lux. Brighter would interfere with things like sleep. Darker would mean a longish time to adapt after turning off a light. Tropical moonlight would be a bit bright I think so let's aim for the lower end of .3 lux.

For a 3m X 3m room we would have around 10m2 to illuminate. Lux is lumens per square metre so to hit .3 lux we would need 3 lumens. LEDs with an efficacy of 30 lumens/watt are available so our power budget could assume around 0.1W per lamp. Since this is mostly best case I'll double the assumption to 0.2W. It would likely take 7 of these lamps to light my house. So the total power draw is 1.4W giving us a yearly power consumption of 12 kW/h. That would cost me $0.72CAN a year.

The fixtures could be built in at time of construction. Retrofit would be easy as you would only have to snake in something like alarm wire to power the lights. The lights could be designed to run off the door bell transformer. If instead you ran them off a small sealed lead acid battery charged from a wall wart you could claim that you had established a sort of residential emergency egress lighting system.

The proposed level of lighting would of course mostly serve for navigating through the house. This would still simplify things. Most rooms would not need any ceiling lights and associated switches/wiring. Hallways and stairways would not need three way switched lights.

In general safety would be greater at night. I used to fall over the stool in my kitchen on a semi-regular basis before I installed my always-on counter light. I did get quite good at it but it would be unrealistic to think I would not eventually do it badly. The compact fluorescent that lights my basement stairs sometimes likes to wait just long enough for me to miss the top step before producing light after I turn it on. A little bit of light would help there too.

Our house of the future would probably need some built in higher level lighting. A ceiling mounted light for the dining room table is nice. Vanity lighting for the bathroom mirror is essential to allow the residents to maximize their apparent reproductive fitness. Kitchen counters and the stove would need bright lighting. Pretty much the rest of the lighting inside the house would be provided with lamps.

When one deals with lighting one is dealing with some fairly primal stuff. I always need to turn on the main light in the bathroom before having a bath. I think I am afraid to go in the dark water. Perhaps at some level I am afraid of alligators. When fluorescent lighting become popular people immediately started illuminating work spaces to some almost insane levels. Legend has it that photographers of that era used to have trouble believing the result of their light meter readings. They were seeing outside daylight levels of lighting inside buildings. A decade or so later "de-lamping" became popular when it became fashionable to care about power consumption. My point is that people like it when it is bright indoors and the brighter the better. Perhaps low level lighting as a way of life will never become popular simply because of that.

Here are some interesting/related links;

• Don Klipstein's Lighting Info Site
• The LED Museum
• Color Vision
• Scotopic Vision

posted at: 22:37 | path: /ledlight | permanent link to this entry | Comments (0)

Greg Moeller said:

I run normal incandescent in the main and second floor lights, motion sensors turn them on at about 5-10% for just a few seconds so you can walk up/down stairs without tripping. The kitchen has a compact florescent for dim lighting if you're grabbing water, also motion sensed. (5 minute timer on this one)

... which is a good point. You can use your regular lighting at a really low level at night especially if you can tell there is someone there. I guess incandescent is the only common type of lighting that this can work with.

I suppose I can generalize this a bit more. This is really all about low level lighting.

posted at: 16:08 | path: /ledlight | permanent link to this entry | Comments (0)

The issues I wanted to address with this design were my unhappiness with the colour of the light produced by white LEDs and the apparent inefficiency of my second generation design.

White LEDs are blue LEDs with a yellow phosphor that is excited by the blue light. The amount of yellow light emitted is adjusted to produce something that looks like white. You end up with mostly blue and some yellow. (Reference) This light reminded me of dawn for some reason. I apparently don't prefer that part of the day. Recent research strongly suggests that blue light is the portion of the spectrum that synchronizes the circadian rhythm in people. In general blue light tends to wake people up, even at surprisingly low levels. That is pretty much the last thing you want to have happen when you are on a late night bathroom mission. Thus we can assume that my bias had some level of backing from actual science. I decided that I might be happier if I had a light source without blue light that would still allow colours to be distinguished.

If one wants to use LEDs (and I totally did) you are left with some sort of mixture of light from single colour LEDs. People make white light by mixing red, green and blue LEDs. Since I wanted to get rid of the blue that left red and green. I knew enough about colour vision to know that the RGB thing is a bit bogus so I decided to throw in something in between. Yellow was the only colour left over in my LED assortment so I ended up with a RYG mixture. The first combination I tried worked well enough:

I tack soldered some LEDs together and did some testing. I had 4 LEDs worth of voltage so I doubled the yellow component on the basis that I did not like green as much and the red was not very well perceived by human vision. The resulting light did not look very white. It did not really look like anything I could describe to anyone. Sorta greenish yellow. ...or yellowish green. ...but not really. I tested my ability to distinguish colours with the colour photographs in a magazine. I was surprised to see that the colours could not only be distinguished but actually looked more or less OK. Dark blues came out black of course but the colours seemed more or less right. Even the skin tones looked sorta normal which is the last thing I expected to see with light that looked yellow/green. I tried blocking the red LED as it did not seem to be contributing all that much to the mixture. The colours immediately went really strange. In fact blocking any one of the 3 colours made the colour rendition quite noticeably worse.

My extensive research on the light source now complete I turned my attention to the efficiency issue. The root of the problem is that all illuminated surfaces have to be below the level of the edges of the pot shade. The LEDs have to be below the top edge of whatever is shading the wall. The top edge of whatever is shading the wall can not be higher than the edge of the pot. The pipe cap shade used in the second generation light needed to be fairly tall because of the curved position of the LEDS. This put the LEDs fairly low in the pot shade. This caused the LEDs to spend much of their light illuminating the blackened interior of the pot shade.

Here I hit a bit of a creative crisis. Up this point I had been exclusively using plastic pipe end caps to build my lights. The problem is that they do not have many straight edges. So I ended up betraying my medium with the use of aluminium sheet as a wall shade. Here is the actual drawing I used to visualize the angles:

This is a side view of the flat top LED and some 1/16 inch (1.6mm) aluminium sheet bent at a 90 degree angle. This gives a shadow with an edge that extends up at around 60 degrees. For the pot shade I used some 2 inch (50mm) water supply pipe thereby extending my run of misusing plumbing supplies. Here are some pictures that pretty much show what I did next:

A few notes on the proceeding pictures:

• Hanging the pot shade from a single screw is not very secure.
• I messed up on the bending. I cheated and just trimmed the corners of the wall shade based on my knowledge of the size of the room.
• I tried to polish the aluminium. It helped a bit but was probably not worth the bother.
• The resistor value is 150 Ohms. With a 12V supply this works out to about 15mA which means that the light consumes about 0.2W.
• The light mixture is nothing like the colour shown in the shade test picture.

There is what the light looks like on the wall. Rumour has it that there are solvents that can be used to remove the text from the pipe. I seem to have some sort of function over form thing going on right now so I'll probably leave the text.

This is what my bathroom looks like at night. I adjusted the angle of the wall shade once everything was in place. The yellow fan of light on the wall behind the light could be eliminated by blackening the inside of the pot shade. I will probably not bother as it is fairly dim. It is yellow because the yellow LEDs are outermost so they are closest to the inside of the pot shade. Again, the weird colour shown here is not realistic. The light is actually a different weird colour.

So far I am happy with the results. The light is not entirely mixed when it hits the ceiling and so looks a little yellow/green blotchy on the ceiling. I noticed that for approximately a day. I suppose the inhabitants of other planets might associate things with the colour of the light but I do not get out that much so I really do not notice it now. It does seem brighter than the last light. It is using twice the power so that fact does not prove much of anything about the design.

The question of what this all means will be addressed in a future episode...

posted at: 15:24 | path: /ledlight | permanent link to this entry | Comments (0)