Do you think lighting is a big energy deal? Count the lights
in your home. We have 58 fixed lights, 11 moveable lamps, 5 flashlights, a
bunch of candles, and an oil lantern.
Lighting is 35% of Commercial Energy Usage, and 14% of
Residential. And a substantial fraction of lighting is used during the daytime
because almost all Commercial establishments are indoors.
Meanwhile we screen out free sunlight with roofs, walls, blinds,
and even our windows are coated to reduce the light coming in.
Why don’t we use this free sunlight? There are lots of
“reasons:”
- It heats up the room.
- It’s only available near windows.
- The ultraviolet, UV, in the sunlight bleaches and ages furniture and can cause sunburn and cataracts.
- The infrared, IR, heats everything up, whether we want it or not.
- It moves during the day, and we can’t direct it to where it’s needed.
- It’s too variable, sometimes too bright, other times it’s cloudy so there isn’t enough light.
- We still need light at night when the sun has set.
I love the light given off by our wood stove in the winter,
but it’s hard to read by unless you are very close, and then you get too hot. I
don’t see how Abraham Lincoln managed to study by firelight.
I have always been intrigued by Light Pipes, but have never
found a practical application in any of my homes or offices.
So I have long had the idea of using “free sunlight” but never found a practical way to do it, other than the old fashioned way: have lots of windows, and lots of supplementary lights – we have 20 windows and 3 mostly glass doors.
My ideas of filters and mirrors and lenses were always too
complex and too static to be practical.
Then last summer I saw an exhibit of Steven Knapp’s
Light Paintings at the Hyde Museum in Glens Falls, New York. WOW! They are
simply stunning: so vibrant, so colorful. Knapp uses filter/mirrors to tailor
the light to just what he wants: color, shape, intensity, and locations.
As an engineer another thing that struck me is how simple
they are to produce (of course using Steven Knapp’s incredible technical skill
to design the filter/mirrors).
While these light paintings are static, thinking about
Autonomous Vehicles made me realize that we could easily move the light around
as needed: because the sun shifted, or because we want the light in a different
place, or because we wanted a different intensity or color of light.
Reading, eating a romantic dinner, preparing the dinner,
dozing in your easy chair, all require different colors and intensities of
light. We could have them all whenever and wherever we want.
First, we can collect the sunlight we are currently
“throwing away” on the roofs and walls of our buildings. When directly
overhead, sunlight delivers just
over 1 kilowatt per square meter at sea level. Of this energy, 527 watts is
infrared radiation, 445 watts is visible light, and 32 watts is ultraviolet
radiation.
For comparison, 5’ from a 100 watt bulb gives less than 4 watts
per square meter, or less than 1/250 as much as the sun, and your microwave and
hair dryer use about 1 kilowatt of energy. Our house is about 100 square meters, so allowing for the angle of the sun, that's about 50 kilowatts of energy or 150,000 BTU/hour, which is the size of our furnace. If we turned on all the lights in our house at once it would use about 5 kilowatts of energy, but produce only the equivalent of about 50 equivalent total watts of light on the surfaces (less than 1% efficient), compared with the 44,000 watts of visible light from the sun.
Then we concentrate the light so that we can process it
efficiently in a reasonable volume. Then filter out just the frequencies or
colors we want.
For example we can separate the Ultraviolet – it’s perfect
input to solar collectors because of the high energy in each photon. We can
also separate the Infrared
or “heat” and use that as a source of high quality heat in our Integrated
Heating & Cooling System – with mirrors and lenses we can get very high
temperatures if we want, which is why I say it is “high quality heat”.
What happens at night or when clouds and rain diminish the
sunlight? Our answer today is to have lots of artificial light fixtures to meet
the various needs: locations, intensities, and moods.
Instead of lots of separate light fixtures, we could have
just one light source and use the same light processing and distribution system
I’ve described above to filter and distribute it. Thus we can use a very
efficient light source, rather than lots of inefficient ones. And we can easily
install new technologies as they become available to be even more efficient.
Surprise, another role for innovation!
The efficiency
of turning energy into visible light, varies widely depending on the type
of lighting device, and even on the specifics of the device, including it’s wattage.
Here are some sample efficiencies:
- Candle 0.04%
- Gas mantle 0.15-0.3%
- 40 W incandescent 1.8%
- 100 W incandescent 2.6%
- LED bulbs 4.2 – 14.9% (theoretical limit for white light is 38.1% – 43.9%)
- Arc lamps 4.4% - 11.4%
- Fluorescent 8% - 15.6%
- Gas discharge 9.5% - 29% (I believe I’ve seen these in the ceiling fixtures at Costco)
So we can gain a factor of 10 over conventional incandescent
lights. Efficiency tends to increase with power level and to some extent with
voltage level. Also the most efficient light sources aren’t the sort of things
you would have on your bedside table, at least until LED bulbs get closer to
their theoretical efficiencies. Thus the ability to choose our light source
based on efficiency and other characteristics, rather than whether it fits in
our table lamp or our ceiling fixture, is a major energy advantage. And we can
anticipate that the technology will continue to improve, so having the
flexibility to easily upgrade will also be important.
Next up is more on sharing.
