Summary

Lighting can use 25% of a household energy bill, so it is worth doing the numbers to save waste.

Incandescent lights, with the white hot tungsten filament, are only 2% efficient. 98% is wasted as heat. Compact fluorescent Lights CFL are 8-15% and the new LED lights are 8-22% efficient.

LED lights are claimed to last 50,000 hours, (25 years), 35 to 50 times longer than incandescent lighting, and about 2 to 5 times longer than fluorescent lighting.

As well as economy lighting can vary in quality. Some light sources show colours accurately, while some lights have colours missing.

Efficiency and quality

There are two challenges in lighting:

1: the efficiency of how much energy is needed to produce the light.

2: The colour and quality of the light.

Comparing Lights 

How much light do we need?

The design of the reflector and the distance make a dramatic difference to the size of the light and how much is wasted.

The table below gives the lumens a light needs to produce the desired lux.

So bringing the light closer to the source and not spilling any, can dramatically save power.

We can produce these light levels with the following lights:

So a desk lamp with a 40 W incandescent globe shedding all it's light over 0.5 sq metre will give about 900 lux which is suitable for study. 10 Watts of CFL, or 8 Watts of a good LED, will do the same.

The new GE LED light due mid 2014 has different specs. 1,600 lumens, 27 watt of power, 3,000^oK, dimmable, life 25,000 hrs, self cooling, cost $29-39, .

It is very difficult to get consistent data on this. The data in the table comes from the Aust. government and Cree LED.

Free sunlight indoors

If you look at the table on the right you'll see that sunlight is 100,000 lux. That is 500 times the illumination needed in a house. So a skylight need only be 1/500 th of the floor area to give the enough light to turn off the lights altogether. Allow for losses so it could be about 1/200 th the area. In a 4 x 4 kitchen = 280 mm square.

Light can be piped along a reflective tube, a hollow clear tube, or optical fibres. Thus dark areas in the depths of a building can be illuminated with beautiful sunlight for nothing.

Ref:  Wikipedia: Light tube,  Solartube

Lumens and Lux

The standard units of illumination we'll use here are lumens and lux.

Lumen is  a measure of the amount of light energy a source puts out.

E.g. a 100 Watt light bulb gives off 1,500 lumens of light.

1 lux =1 lumen / sq m. It is the brightness of a position, eg a surface .

E.g. we like to have 220 lux on a kitchen bench in order to see clearly. 

Light levels in lux produced by light sources at different distances.

This has been calculated assuming all light is radiated out in all directions. A mirror shade will recover wasted light, sending it in the desired direction.

Summary of information below​

Comparing Light​s to 50 watt QI down light

Despite wonderful hype and promises on the various websites, a simple comparison can be quite surprising, if expensive. I bought a few lights and compared them with each other.

I used a camera light meter for measuring light level

Some lights produced a spot only, so score was reduced by a very rough visual estimate. I've taken a QI down light to be 100% and made a very rough judgment on the other lights. It is simply a rough and ready check on the manufacturers specs showing lumens.

LED = Light Emitting Diode

CFL Compact Fluorescent

Downlighting - 60º wide flood beam angle version is ideal for general illumination. Suitable for Hotels, Apartments, Office & Sh​oplighting
Spot Lighting - 30º spot beam angle version is ideal for accent lighting. Suitable for Museums, Hotels, Apartments & Shoplighting

Brightgreen manual

Efficiency of light sources

Very little light energy is produced by most light sources. Most of the energy is given off as heat.

Lumens are a measure of visble light.

A perfect light would produce 683 lumens of light for every watt of energy and it would be 100% efficient at producing visible light. We are most interested in how many lumens of light is produced per watt of electricity put in.

It is also interesting to know how efficient the process is. All real light sources produce Infra red, IR, (heat) and sometimes UV as well. If is not visible so is counted as 0 lumens.

So to work out how much light a 100 watt incandescent globe will produce:

15 lumens/Watt x 100 Watts = 1500 lumens.

Gravity light

Because LEDs require so little energy, they can even be run with simple wind-up mechanisms. One charity has designed a light to be run by a weight on a rope. Pull the loose end of the rope to lift the bag of stones and this stored potential energy can run the light for half an hour. Very similar in design to the old grandfather clock.

It can also charge batteries.

The light is not powered by gravity, energy is simply stored as potential energy.

 Video

Cost savings of LED or CFL lights

Cost of an LED light

A 10.5 watt LED in its 50,000 hour (25-30 years) lifetime will consume about 525 kilowatt-hours. At say 30c/KWh this will cost $160.  During that time, it will never need to be replaced.

The Cost of Incandescent Lamps

 To match the light output and longevity of an LED light it would consume 3,250 kilowatt-hours, costing over $1,150 at todays prices. As well it would need to be replaced about 25 times. 

A typical 65 watt incandescent light lasts for 2,000 hours. 

Compact Fluorescent Lights CFL

CFLs are simply miniature versions of full-sized fluorescents. They screw into standard lamp sockets, and give off light that looks similar to the common incandescent bulbs - not like the fluorescent lighting we associate with factories and schools. The will use a little more power than the LED and be replaced about 5 times.

Coloring Rendering Index (CRI)

CRI represents the quality of light and its faithfulness to render colors correctly, that is, to enable us to perceive colors as we know them.

The ideal CRI is 100, and some incandescent bulbs approach this level.

LED bulbs CRI ratings range from 70 to 95.

The best CFLs have ratings in the mid 80s. 

Black body radiation

If a block of black carbon is heated it will become red hot, then yellow hot, white hot, them blue hot. 

There is a different amount of energy given off at each wave length (colour) for each temperature.

The temperature is always given in degrees Kelvin. This is a temperature scale starting at absolute zero (-273^oC). To convert Kelvin to Celsius subtract 273.

Energy given off at various wave lengths (colour)

Correlated Color Temperature (CCT)

CCT is the measure used to describe the relative color appearance of a white light source. CCT indicates whether a light source appears more yellow/gold/orange or more blue, in terms of the range of available shades of "white." CCT is given in kelvins (unit of absolute temperature). 2700K is "Warm" and 5000K is "Cool". The typical light color we are used to in indoor home lighting is "warm", 2700 - 2800K.

Emission spectra

There are other ways of producing light. They all involve exciting the electrons in the outer shell of an atom raising them to outer energy levels (orbital), then letting them fall back to their original energy level. The may happen in stages. Each fall down an energy level gives off a single pulse of light called a photo. Each energy difference produces a photon with an exact wave length.

So, if we excite sodium vapour, it will give off only two wave lengths.

Each element gives off it's own emission spectra and this is used to detect elements ina sample.. The process is also very efficient converting  energy into light.

The problem is that it looks awful. If we look at a loved one under sodium vapour light it will only reflect yellow. Any other colour will look black.

Here we can see the yellow of sodium vapour, the green of mercury, and the warm light for another source.

Flame

A fire is a mixture of red hot carbon and gas, and emission spectra from various elements in the flame.

You can see that the remaining daylight on the snow is very blue in comparison to the fire. Our eyes normally adjust to this and we don't see it until the photograph is printed.

Sometimes the waste heat is welcome.

The colours in fireworks come from burning different metals which give off their characteristic emission spectra.

Red is strontium, or lithium, Orange - calcium, gold - iron, yellow - sodium, green - copper or barium,  More

Calculating lux from lumens

Area of sphere = 4 pi R²

12.6 lumens will produce 1 lux at 1 metre.

After that divide by 12.6  (4 x pi)

e.g. 12.6 lumens will produce 1/9 lux at 3 Metres

Lux = Lumens/4 pi R²

         = 0.796 x Lumens /R²

New rese​ar​ch

Field-induc​ed polymer electroluminescent (FIPEL)

Scientists at Wake Forest University have developed a flicker-free, shatterproof alternative for large-scale lighting that they claim is at least twice as efficient as CFL technology and less expensive than LEDs. The lighting is based on field-induced polymer electroluminescent (FIPEL) technology, which uses a nano-engineered polymer matrix to convert the charge into light.
 

Induction light

An electrodeless lamp or induction light is a light source in which the power  is transferred into the lamp via electromagnetic fields. A normal electrical lamp uses metal connectors. There are advantages:

• Extended lamp life, because the electrodes are usually the limiting factor in lamp life.
• The ability to use light-generating substances of higher efficiency that would react with metal electrodes in normal lamps.
• Improved collection efficiency because the source can be made very small without shortening life, a problem in electroded lamps

In plasma lamps, radio waves energise sulfur or metal halides. A microwave beam can light a lamp 1,000 KM away.

Fluorescent lamps can be driven by a magnetic field.

Theoretically they have high efficiency and life. However present models are not yet achieving either.

Wikipedia