Luminous Efficiency of Lamps

This article compares the incandescent bulbs with bulbs halogen-30% and 50% of energy as well as the 12V models.

The luminous efficiency of a light bulb is expressed in Lumens per Watt. It depends on the type of bulb but also, to a lesser extent, of his power.

Definition of the lumen

The lumen (symbol lm) is a unit of light output as the watt (W). As the conversion between dollar and euro, we have:

1W = 683 lm (at 555nm)

This conversion is valid only for the wavelength 555nm (maximum sensitivity of the eye in daytime vision). For a color where the sensitivity of the eye is 60% of the maximum (orange or turquoise for example), 1 watt will give that 683lm x 60% = 410 lm. An optical power emitted to 350nm or 900nm is not perceived by the eye and therefore generates no lumen.

In the case of white light, the report by lm/W is less than 683 because the average sensitivity of the eye, for all the colours present in the White is less than the maximum. The report is worth 240 lm/W. This is not a performance but a conversion like that between minutes and seconds: there is no energy loss between the emitted optical watt and the 240 lm perceived by the eye.

A few luminous efficiencies

683 lm/W: wavelength 555nm monochromatic

240 lm/W: white light

95 lm/W: light emission of a black body brought to 6300K (temperature where there is maximum light efficiency)

approx. 48 lm/W: luminous efficiency of tungsten on 3695K (melting point)

For electric lighting:

up to 200 lm/W: power LED (2011)

luminous efficiency of the lamps lumen per watt 0

Effectiveness of a mark CREE LED: 200 lm/W

40 to 100 lm/W: low consumption and fluorescent tube light bulb

40 lm/W: bulb halogen 24V/250W 50 h of life

14 to 30 lm/W: halogen 12V

10 to 23 lm/W: 230V halogen bulb

7 to 14 lm/W: classic incandescent bulb

0.2 to 0.4 lm/W: candle flame

Logarithmic scale with light efficiency

Luminous efficiency of incandescent and halogen bulbs

The following tables below are the synthesis of values noted in supermarkets in the light bulb aisle. All light bulbs with white light, compared with comparable luminous efficiencies.

Incandescent bulb

(Obsolete or almost 2011) incandescent bulb

luminous efficiency of the lumen per watt 3 lamps

Power, luminous flux and luminous efficacy (lumen per watt)

More the power of the bulb, the more the filament is thick. For a life equal (1000heures), its temperature can be higher, where better light efficiency.

230V halogen bulb: Energy Saver-30% of Osram or Ecoclassic30 of Philips

Different bulbs halogen 30% saving of class C and D (up to date in 2011!)

luminous efficiency of the lumen per watt 5 lamps

Power, luminous flux and luminous efficacy (lumen per watt)

Light bulbs halogen 230V Ecoclassic50 of Philips (class B)

luminous efficiency of the lumen per watt 6 lamps

Ecoclassic50 shaped “flame”

Ecoclassic50 shaped “flame”

Transparent and frosted Ecoclassic50 “ivory”

The Philips Ecoclassic50 are actually the bulbs low voltage 12V with an electronic transformer built into the base, under the hood metal at the bottom of the bulb. The use of low voltage is the secret of the high luminous efficiency.

luminous efficiency of the lamps lumen per watt 9

Power, luminous flux and luminous efficacy (lumen per watt)

Standard 12V halogen bulbs

Power, luminous flux and luminous efficacy (lumen per watt)

Halogen 12V IRC Osram bulbs

IRC (“Infra Red Coating”) technology is to place a transparent coating to the light but that reflects the infrared (heat) into the filament. Therefore the filament hotter. There thus need less energy to maintain a given temperature.

For the buyer, light bulbs 12V IRC are characterised by a form of typical strangled bulb. The filament is rather in a sphere, not a cylinder.

luminous efficiency of the lamps lumen per watt 12

Example of halogen 12V IRC

These bulbs are announcing 30% of energy consumption compared to the conventional 12V

luminous efficiency of the lamps lumen per watt 13

Power, luminous flux and luminous efficacy (lumen per watt)

Graph of the luminous efficiencies

Luminous efficiencies of different types of bulbs are summarised on the chart below.

luminous efficiency of the lamps lumen per watt 14

Luminous efficiencies compared on various types of light bulbs

There is a look of growing curve for each type of lamp. For more powerful models, the manufacturer can calculate the filament to make it hotter. Faster evaporation at high temperature is compensated by the thickness of the filament.

Equivalent to a certain power models are not quite equivalent to this power. They certainly save the advertised power (-30%, -50%) but restore 90 to 95% of the equivalent power. For example, an equivalent bulb 100W is approximately equivalent to 92W.

Another document provides these results of measurements compared to the energy classes B and C.

luminous efficiency of the lamps lumen per watt 15

Luminous efficiencies measured

Conclusion

Tungsten filament bulbs efficiency is improved by low voltage 12V supply and using a bulb IRC. A 230V/12V transformer built into the bulb allows applications in direct replacement of our old good bulbs incandescent.

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