How to Choose Home Lighting: Incandescent, Fluorescent, CFL, LED, Sodium, and Metal Halide
What Lighting Should I Use?
Did you know that a "normal" incandescent light bulb only converts about 5% of the electricity used into useful light? The remaining 95% ends up as heat. There are lots of other options in home lighting which are much more efficient.
In this article I cover the pros and cons of various interior and exterior lighting types, give a simple explanation of how the lamps work and how they compare in terms of energy cost, price and lifespan.
What Difference Does it Make What Lighting I Use?
Well basically some lighting types are more efficient than others and use less electricity while producing the same light output. However there are other issues to consider when buying lamps and light fittings such as the initial cost of lamps/light fitting, lifetime of bulbs and the color of light produced.
- Ballast or Switchgear The electrics/electronics used for controlling the switch on and regulation/limiting of current passing through a lamp
- Lumens The output light flux from a lamp. A traditional 100 watt incandescent bulb gives out about 1600 lumens of light
- Candela or millicandela The brightness of a lamp. A reflector at the back of a lamp (eg on a floodlight or car headlamp) increases the brightness in the forward direction, even though the lumens output of the lamp stays the same.
- Luminous Efficacy Output in lumens per watt of electrical power input
- PIR Passive Infra RED. A technology used in switches for turning on a light when someone walks in front of the PIR sensor
Types of Lamps and Lighting
Lamps are the parts of a light fixture which actually produce the light output. There are several types and all have their advantages and disadvantages.
Lighting can be broadly divided up into incandescent, discharge and LED types.
Incandescent lighting is based on the principle of heating a metal to a high temperature. At temperatures of over 1000C, metals glow white hot.
- Standard incandescent bulb
- Quartz halogen tube
- Halogen bulb
- Halogen spotlight
Standard Incandescent Bulb
This is the original form of lighting which has been used in the home for over a hundred years. Bulbs or lamps consist of a glass envelope containing a filament made of tungsten or similar metal of high electrical resistance and melting point. An electrical current is passed through the filament which glows white hot and radiates light and heat. The glass envelope is filled with an inert gas such as argon to isolate the filament from oxygen in the air and prevent it from burning out.
Incandescent bulbs are made in all sorts of shapes, sizes, wattages and base styles; bayonet cap (BC) and Edison screw (ES). They are also the least expensive type of lamp and don't require any special holders or electronic/electrical switch gear. They can be plugged into a simple holder. However they are woefully inefficient in terms of light output versus energy input. An incandescent bulb converts most of the electricity input to heat - typically about 95%. So these types of lamps are basically glorified heaters! Lifespan of a bulb is the shortest of all types of lighting at approx 1000 hours.
Cost of Running a 100 Watt Incandescent Bulb
If a bulb is switched on for about 10 hours per day in the winter, and 4 hours per day in the summer, this works out at 7 hours per day on average for the whole year.
So this is 365 * 7 = 2555 hours per year
Cost per kilowatt hour (kWh) or unit is about 12 cents
Cost of running bulb = (power in watts / 1000) x number of hours running time x cost per unit
= (100/1000) x 2555 x 12
Quartz Halogen Lamps
These take the form of a tube about 1/2 an inch in diameter and from 3 to 5 inches long made of quartz glass. A tungsten filament is mounted internally in an inert gas to which a small amount of a halogen such as bromine or iodine is added. In a normal incandescent lamp, tungsten vapor "evaporates" from the filament blackening the glass envelope, reducing the light output and the lifespan of the lamp. This phenomenon would become more severe as the temperature of the filament increases. An object becomes more efficient at radiating light as it becomes hotter. So it is desirable to increase the efficiency of a lamp by increasing the filament temperature .The added halogen combines with evaporated tungsten producing a halide, effectively "mopping up" the tungsten and keeping the quartz clear. So the lamp can be run at a much higher temperature and this increases light output for a given wattage. The quartz glass envelope is important in order to withstand high temperatures, and the increased pressure also reduces tungsten evaporation from the filament. These lamps are commonly used in exterior floodlights (e.g. 150, 300 and 500 watt types). The disadvantage is that the lighting fixture can become quite hot and must be kept at a minimum distance from flammable materials to reduce the danger of fire. The lamps are prone to failure also as dampness condensing on the surface of the tube due to moisture in the fitting, or from the lamp being touched during installation, can cause failure. This is because hot spots caused by contamination can crystallize the glass making it leak or rupture.
These are shaped like standard incandescent bulbs and available in similar wattages and shapes. However they contain a quartz halogen capsule. They use about 70% of the energy of a standard incandescent bulb. The commonly available 50 watt spotlight bulbs are of the halogen type.
These are usually 50 watt and are commonly available in a light fixture which takes 3 or 4 lamps which can be pointed in different directions. So they can be used in a kitchen for instance for concentrating light onto a worktop.
Discharge lighting works on the principle of passing an electric current through a gas. This ionizes the gas, and the electrons give out light as they return to their non-excited state. This is similar to how an electrical spark from a spark plug or lightning produces light.
- Sodium vapor
- Metal halide
Fluorescent tubes are a type of discharge lamp. They contain a gas and mercury vapor. When a fluorescent lamp is switched on, a current passes through filaments at the end of the tube causing them to glow. This produces electrons in the vicinity of the filaments. A high voltage pulse then "strikes" the tube causing electrons to be accelerated down the tube. These electrons collide with atoms of the mercury vapor and excite them, making their electrons jump to higher orbits and then fall back, radiating UV light in the process. This radiation hits the inner surface of the tube which is coated with a phosphor and the UV is converted to visible light.
Fluorescent lamps give 4 to 5 times more light output per watt compared to incandescent bulbs. However the tubes are more expensive and special fixtures incorporating switchgear for controlling the lamps are required, adding to the cost. In the medium term, fluorescent lighting pays for itself because of the lower running costs. So it is used widely in the workplace and stores. The disadvantage of fluorescent lighting is that the spectrum of the light veers towards the green and blue end of spectrum unlike the warm glow of incandescent lighting. However tubes are commonly available which somewhat correct this at the expense of light output. Another disadvantage is that the flicker of fluorescent lighting can be irritating to some people and could trigger epilepsy or migraine in susceptible individuals. Newer type electronic ballasts in fixtures raise the flicker frequency and this may lessen the potential for this occurring.
Fluorescent tubes are available from 4 inches in length to 8 feet long. Variations in shape are available e.g circular shapes.
CFL (Compact Fluorescent Lamp)
A CFL is basically a folded up fluorescent tube. The plastic section of the lamp incorporates the switchgear. This is electronic, and the switching frequency is high, minimizing flicker, unlike older type inductive ballasts. CFLs act as "drop in replacements" for standard incandescent lamps, and like fluorescent tubes, their efficiency is higher than that of incandescents. So a 20 watt CFL is equivalent to a 100 watt incandescent (In practice it is closer to about 90 watt). CFLs have dropped in price over the years as production and demand has increased. This is due to mandatory bans on widespread incandescent lamp use in some countries in order to reduce energy consumption.
Sodium Vapor Lamps
Sodium lighting will be familiar to you in the form of the orange/yellow lamps used to light our streets. This is another form of discharge lighting just like fluorescent lamps. The tube is made of borosilicate glass to withstand pressure and temperature and contains some sodium metal, neon and argon. When the lamp is switched on, the sodium vaporises and an arc is established. There are various types of sodium lamps; high pressure. low pressure, SON, SOX etc. Sodium lighting has the highest efficiency of all lighting. This is due to the fact that the light output is in the yellow range of the spectrum and the human eye is most sensitive in this region. However there are several disadvantages. Firstly it takes several minutes for a lamp to reach full brightness, so switch on by a PIR is not an option. Also switchgear is necessary to control the lights. Because the light output is yellow, this can be a problem where color rendition is important. Sodium floodlights are advantageous for lighting up a yard or garden for instance because of the low running cost, and the light can be switched on at dusk by a photoelectric switch.
Metal Halide Lighting
Another form of discharge lighting. Not quite as efficient as sodium, but the light output is white in color so it is useful for lighting up a yard for instance when color rendering is necessary. The lamps contain gases such as xenon and a mixture of mercury and metal halides. Metal halide fittings are used for flood lighting sports stadiums, car parks, store yards etc. and as display lighting in stores. The lamps are also used in car headlights (the ones which appear slightly bluish)
These devices work on the principle of light emission produced by passing a current through various types of semiconductor material. The lamps are made up of a structure onto which hundreds of LEDS are bonded. LED lighting is steadily replacing other types in numerous applications such as domestic lighting, workplace and street illumination and vehicle lighting. LED lamps/bulbs offer many advantages. Firstly they are even more efficient than CFL. Another advantage is that they run cool and produce less heat output. They are rugged and don't have a fragile glass envelope unlike a CFL. They are available in a multitude of colors and are easily dimmable. At present, they are quite expensive but costs will fall as production and demand increases.
LED lamps have a theoretical lifetime of 50000 hours, 50 times that of an incandescent light bulb. LED lamps are available as drop in replacements for standard incandescent bulbs, halogen spotlights, halogen tubes in floodlights and fluorescent tubes.
A 100 watt incandescent bulb can cost up to $30 a year to run, if switched on for about 7 hours on average per day. An LED lamp will cost only about 1/5 of this to run.
Outdoor Lighting and PIR Sensors
When controlled by a PIR sensor which detects someone walking by, a lamp should light up instantly. Bulkhead or similar light fittings can be fitted with incandescent or LED lamps which are suitable for this application
Luminous Efficacy (lumens/watt)
Color of Light
10 - 15
Least expensive lighting, no switchgear needed, reach full brightness instantly
Low efficiency, shortest lifespan (1000 hrs)
20 - 25
Relatively cheap - no switchgear needed - more efficient than standard incandescent
Run very hot
50 - 80
Warm White, Cool White
Very efficient, run relatively cool, 5000 hr life span
More expensive than halogen or incandescent, special fixture needed
50 - 90
Very efficient, run cool, drop in replacement for incandescent bulbs, very long lifespan (50000hrs), reach full brightness instantly
Expensive at present
80 - 200
Most efficient form of lighting
Expensive, switchgear needed, take a long time to reach full brightness, not suitable when it is necessary to differentiate between colors
60 - 120
Very efficient but not as efficient as sodium, light output is white
Expensive, switchgear needed, take time to reach full brightness
Questions & Answers
© 2012 Eugene Brennan