Filament lamp

Work in progress. Best not to rely on information here yet, errors and omissions can occur.

Terminology

Lamp

Lightbulb (the bulb only)

Fitting, luminaire

The whole lighting appliance, into which the lamp goes

Efficiency

Light output per power input. However this does not take into account that perceived brightness per output varies considerably depending on the spectrum of the light, so it doesn't tell us the brightness per power in figure.

Efficacy

Light output brightness per watt input. The best measure of lighting energy efficiency.

Cap

The base of the bulb, the bit that connects to the bulbholder.

Lighting Glossary

History

The first metal filament incandescent lamps from the early 1800s used a platinum filament. They were extremely short lived and prohibitively expensive, and never considered practical.

The practical carbon filament lamp was invented in the late 1800s, and provided lighting at around half a percent efficiency for several decades. Carbon lamps are rarely seen outside of museums today.

Filament lamps as we know them today have a metal tungsten filament. Tungsten filaments have been with us since 1910. Gas fill was introduced in 1913, preventing blackening and improving light output. Practical frosting was invented in 1924. The development of the coiled coil filament in 1936 increased efficiencies further, and this is the type of GLS filament lamp we use today. Efficiencies vary but are in the region of 2%.

Halogen lamps, popularised in the 1970s, feature some improvements which raise the efficiency of filment lamps a little. However they come with their own issues.

The latest chapter in the filament lamp story is HIR lamps with IR reflecting envelopes. By reflecting IR back to the filament, less electrical power is needed. These are still low efficiency lamps though.

Bases/Caps

• BC or B22d: Bayonet cap, Britain's most popular lamp base.
• ES: Edison screw, our 27mm version of America's most popular lamp base
• SBC: Small bayonet cap
• SES: Small edison screw, 14mm
• M17: 17mm screw cap, used for some appliance lamps
• MES: Miniature edison screw, used for torch bulbs only.
• Tubular: 221mm and 284mm filament striplights with a connector at each end.
• Linear halogen: short linear lamps

Popular domestic filament lamp types

PAR reflector lamps (parabolic aluminium reflector) produce a narrower beam than non-PAR reflector lamps.

• GLS A series - pictured above, 15w to 200w
• Golfball - small round, upto 60w
• Globe - large round, apx 4" dia, typ 60-100w
• Candle - decorative for chandeliers etc
• R50 - 50mm reflector, typ 40w
• R63 - 63mm reflector, typ 60w
• R80 - 80mm reflector, typ 60w
• R95 - 95mm reflector, typ 100w
• PAR38 - apx 5" reflector, hardened glass, rainproof. Typ 100-150w
• Crown silvered
• Tubular filament - striplight, 221mm or 284mm, 30w & 60w
• 12v halogen reflector, 20w - 150w
• 12v halogen capsule (G4) 5w - 150w
• 240v halogen (GU10, G9)
• 240v halogen GLS replacement
• Linear halogen - 150w, 500w, 1kW & more

Filament lamp specs

These figures apply to standard filament lamps. Long life lamps will have lower output and energy efficiency figures.

• Power consumption in watts (w)
• Light ouptut in lumens (l)
• Energy efficiency in lumens/watt (l/w)
• Average life in hours (hrs)

GLS, Golfball, Candle, Globe, R50, R80, R95, PAR38: 1000hrs, typical figures only:

• 15w
• 25w 200-250l 8-10 l/w
• 40w 400l 10 l/w
• 60w 660-700l 11 l/w
• 75w 900l 12 l/w
• 100w 1300l 13 l/w
• 150w 2100l 14 l/w
• 200w 3000l 15 l/w

Tubular filament:

• 30w 190l 6.3 l/w 1000hrs
• 60w

Halogen:

• 12v halogen reflector
• 12v halogen capsule
• 240v halogen reflector (GU10)
• 240v halogen GLS replacement
• Linear halogen
  • 150w
  • 500w
  • 1kw

Miniature lamp bases

BC and ES bulbholders can be installed on 5A, 6A or 10A lighting circuits. Most domestic lighting circuits are 5A or 6A.

SES and SBC bulbholders are not permitted to be installed on 10A lighting circuits.

SES and SBC lamps are often more expensive, and add yet another lamp type to keep in stock. Its thus better to only use them in applications where the smaller cap size is really needed, which means chandeliers and existing fittings such as fridges.

Appliance Lamps

Cookers, fridges and microwaves commonly use small filament lamps for interior lighting. Some of these have:

• hardened glass to reduce risk of breakage & contaminating food with broken glass
• higher operating temp spec (for oven lamps)
• M17 bases (17mm)

These lamps are usually designed to run at below 2700K to achieve longer life, at the expense of reduced light output and slightly yellowy light colour.

The differences with appliance lamps are optimisations rather than essential features, and in many cases standard SES lamps can be fitted. These have shorter lifetimes and are easier to break, but are widely available and lower cost.

Appliance lamps not rated for oven use may often be fitted in ovens. These will run outside of the manufacturer's specs, but seem to be ok in practice.

Replacement of hardened glass lamps with unhardened is only advisable where the lamp is behind a physical shield to prevent accidental breakage. Lamps housed in open wire cages should preferably be the correct appliance lamps.

For appliances using hard to find lamp types, replacing the holder with an SES is an option. Many Sharp microwaves use 120v lamps, requiring a minor change in wiring if this is done.

Lamp life

Standard British GLS filament lamps last an average 1,000 hours. Individual lamp life varies, this is only an average figure.

Filament lamps are batch tested, and lamps not meeting the manufacturer's claims would be in breach of the Trades Descriptions Act. In practice its rare to find a batch of filament lamps not meeting their claimed lifetime. Some in the batch will last less time, some more.

See main article Lamp Life

Increasing lamp life

Filament lamps with up to 5000 hr life are available. The energy efficiency of these is much worse than standard 1000 hour lamps, and the total run cost for a given light output significantly higher.

Filament lamps can be wired in series to achieve very long life, but this produces exceptionally bad energy efficiency and excessive run cost. There are better options.

A transformer may be used to reduce the supply to filament lamp by 20v to triple its life. The lamp then behaves as a long life lamp, with the same poor energy efficiency.

Because of increased running cost and energy use, increasing filament lamp life is only a good idea where relamping causes a specific problem. In most such cases other lamp types are used.

Premature failure

Premature filament lamp failure may be caused by vibration, pitted bulbholder contacts or switch contacts, or rarely overvoltage. However most complaints of high failure rate seem to be down to unrealistic expectations. Bear in mind that a lighting scheme with 10 times as many bulbs will experience 10x the rate of failures, and a lot of people grew up with one bulb per room.

See main article Lamp Life for a full discussion.

Bulb Boosting

Light output and energy efficiency of filament lamps may be boosted by running them on slighly increased voltage. This can be of use for light fittings with max power ratings below what's wanted.

Halogen lamps are not suitable for boosting. Nor are 60w golfball bulbs, these already run very close to temperature limits, and may solder themselves to the bulbholder in protest if boosted.

There are 3 ways to achieve the boost:

1. Transformer boost 240v to 260v
2. French 220v bulbs on our 240v.
3. Rectifier and capacitor booster

Transformer boost

A 20v transformer is wired to change 240v to 260v. 20v is an uncommon voltage, 18v & 24v are the closest popular values. See Droppers for details of transformer boost wiring.

French 220v bulbs

When used on our 240v, french bulbs will run at above design voltage. With filament bulbs the result is 30% more brightness and about 300hr life expectancy. More info on 220,230 & 240v

Rectifier & capacitor

Mains is rectified with a bridge rectifier, then a small capacitor placed across the rectified ac. This increases rms voltage without increasing peak voltage, leaving the power still compatible with CFL lights as well as filament.

Capacitor value is adjusted to give the wanted rms voltage boost, which is typically 20v.

A bleeder resistor is added across the capacitor to discharge it when power is off.

An rms reading voltmeter is used to set the right amount of boost. Without an rms meter, the resulting operating point would only be a rough guess, and lamp life could vary from expectation.

Required part specs:

• Bridge rectifier: 1kV, 15x lamp run current
  • 4A for 60w, 6A for 100w
• capacitor: Class X 250v ac
  • Do NOT use non class X caps marked 250v
• bleeder resistor: 270k 400v rated
  • minimum 0.5w. 0.3w & 0.25w not suitable

The one sometimes downside of this method is that the amount of boost applied will change if a different wattage bulb is fitted. A lower power bulb will get more boost with a given capacitor.

Results

A 20v rms boost results in:

• 16% efficacy boost
• 14% power consumption increase
• 31% light output boost
• lifetime reduced from 1000 hours to 280 hours
• Colour temperature increased from 2700K to 2800K

			With 20v boost
Property		60w	100w
--------		---	----
power consumption	68w	114w
light output equiv	80w	130w

Bulb Stocks

The less different types of bulb are used, the easier it is to keep spares stocked.

The more common the bulb types, the more convenient buying them will be, as popular lamps are available from more retailers.

There is talk of banning most filament bulbs on political grounds, and it seems there is a real possibility of this occurring. 2 possible solutions are light fittings that take other lamps types, and stocking up before a ban. Some stores have already withdrawn filament lamps from sale.

PAR38s

These large reflector lamps have a thick hardened glass envelope and may be used outdoors with no protection from rain (in suitable fittings). They are expensive filament lamps, and will waste money on purchase costs if used indoors.

Indoor PAR38 fittings can be fitted with GLS 100w bulbs where the bulb is not directly visible. These give a much wider beam han PAR spotlights, but in most cases this is fine. Occasionally the fitting interior is not white or silver, in which case light output would be reduced with GLS lamps. Painting the interior white avoids this.

Dimming

Dimmers

Dimming greatly reduces energy efficiency of all filament lamps. As an example, a 500w halogen lamp dimmed to put out the equivalent of a 40w bulb was found to consume 300w. Dimmers also preclude use of CFLs, which may be an issue if GLS filament lamps are phased out (which looks fairly likely).

Switchbanks

Switchbanks don't affect efficiency, and are compatible with all lighting types, but are less flexible than dimmers, both in installation and use.

Switchable Boost

Another dimming option is to use bulb boosting with a switchable boost setting. This increases energy efficiency and reduces run cost, but it reduces lamp life significantly, and only gives 2 brightness settings. Real lamp life will depend on the relative amount of time at each setting, and will vary from 280 hrs to 1000 hrs.

If implemented using the BR&C method, this type of brightness variation is fully compatible with CFLs on both settings. Other methods will work fine with CFLs on the non-boost setting. See Bulb Boosting section.

Coloured lamps

Novelty lamps

Filament lamps are available in an array of colours. Since these colours are achieved by filtering out the unwanted colours in white light, all coloured lamps have much lower efficacy than white lights. Blue filament lamps have especially poor efficacy, and when colours are mixed it is preferable to choose higher power bulbs for the blues.

Soft tinted lamps

Lightly tinted lamps can create a warm soft atmosphere. Efficacy is below standard filament lamps, but much better than that of strongly coloured novelty types. These are mostly available with peach and pink tints.

Daylight lamps

Daylight lamps have a blue coating to produce a higher colour temperature (colder) light. These are used when it is necessary to view colours as they would appear in outdoor light. The resulting spectrum is not perfect, but is close enough for many tasks.

Again these have reduced efficacy. 100w bulbs rated at 500l were spotted, versus 1300l for white GLS.

For regular users of daylight lamps, its cheaper to fit a CCT changing gel over a standard GLS lamp, and this avoids the need to buy expensive lamps, and stock another lamp type.

Painted lamps

Painted lamps have limited life. if you wish to keep your work you may prefer to paint a glass globe and fit this over a bulb. Dead painted GLS lamps may sometimes be salvageable by cutting the base off and inserting a halogen capsule lamp. Globe lamps give a bigger canvas.

Violet lamps

Used in cheap electric flykillers. Not very good at attracting flies.

Halogen

Halogen lamps are a more modern form of filament lamp. The fill gas in halogen lamps contains high pressure gas wich reduces filament evaporation, plus a percentage of iodine or bromine that returns evaporated metal back to the filament. These enable the filament to be operated at higher temperature, achieving some improvement in efficiency.

In principle halogens are slightly more efficient than GLS, but in practice the types of lighting halogens are usually used in result in much worse energy efficiency than GLS.

Linear halogen

Linear halogen lamps are available in wattages of:

• 150w
• 300w
• 500w
• 1kW

All but 150w have more light output than is useful in 99% of domestic houses. The majority of outdoor yards and gardens also only need 150w. 500w fittings have their uses for lighting large areas, but are much overused. The result is unpleasant lighting and waste of energy and money.

Outdoor 500w lamps need to be mounted high up (well out of reach) to be effective in illuminating a wide area. 1kW lamps require street lamp posts or similar to make them effective at achieving large area coverage. Without sufficiently high mounting, these high power lamps will effectively cover an area much smaller than their capability, and cause severe glare.

Due to the high power consumption of 500w & 1kW lamps, when continuous lighting is wanted at these power levels its usually better to look at some form of Discharge Lighting instead.

• metal halide produces white light
• high pressure sodium produces pink/orange light (and white sodium is an improved version)
• low pressure sodium produces monochromatic pure yellow light at exceptionally high efficiency.

These discharge lamps can hugely reduce energy consumption and run cost.

Electric sun

Linear halogen lamps are occasionally used to provide artifical sunlight where natural light is insufficient. This may be achieved by mounting a high power lamp near the ceiling by the front door, allowing it to shine through an interior window to produce a pattern that replicates that of the sun shining in through an exterior window. Where this arrangement is not suitable, its possible to mimic window shadows in other ways to make the appearance seem natural to some extent.

HIR lamps

Linear halogen lamps are now available with IR reflecting envelopes. By reflecting heat back onto the filament, less electrical energy is used.

• 375w HIR replaces 500w halogen
• ? HIR replaces 150w halogen

Dimmed PIR lights

PIR lights that run the bulb dimmed suffer a sizeable defect, and often waste thousands of pounds over their lifetime. For details see Dimmed PIR Lights

Mixed lighting

Good results with reduced energy use can be achieved by mixing reduced level background fluorescent lighting with filament lights. This works well if the fluorescent source is 2700K and high CRI. Trying this with another tube type will not work well. Most retailers would need to order in 2700K tubes. 2' tubes are useful for this.

Colour temperature

• GLS lighting is 2700K
• Boosted GLS is 2800K
• Halogen lighting is around 3000K
• Long life lamps are below 2700K
• Tubular filament is below 2700K

Other filament lamps

Soft white

About 11% less lumen output

Other lamp types

• CFL Lamps
• Fluorescent Lighting
• LED Lighting
• Discharge Lighting
• Neon (not very common) (flickering candle flame lamps)

See Also

• Lamp Life
• Wiki Contents
• Wiki Subject Categories