Energy Efficiency of Technologies... A Historical Perspective

Veritas circular Super Aladdin Famos mantle Tilley pressure wick 18CP mantle 60CP lamp 120CP mantle 300CP

A seasonal look back at some ‘vintage’ lights – putting energy efficiency into context

By Phil Harris CEng CEnv CMgr FCIBSE MIEE MEI MCMI, Immediate Past President, SCEME Lighting Technology Timeline For thousands of years, people lived without artificial light...

15000 BC – stone & wick lamps burning animal fat 1000 BC – spout lamps burning whale oil 1000 AD – rushlights (partly peeled rush dipped in tallow) 1300 AD – dipped , made from tallow or beeswax 1400 AD – moulded invented 1700 AD – spermaceti high-grade candle (British Standard Candle*) 1700 AD – Colza (vegetable oil) lamps with flat wicks 1750 AD – paraffin wax candles 1784 AD – Argand burner (circular wick) 1800 AD – development of coal gas for lighting 1850 AD – James Young patents refining process for paraffin (shale oil) 1865 AD – invention of the Hinks Duplex oil burner 1870 AD – central draught burner with circular wick 1880 AD – development of the electric light bulb by Swan and Edison 1885 AD – invention of the Von Welsbach incandescent mantle Duplex wick 1900 AD – wick/mantle oil lamps such as Aladdin, Famos lamp 20CP 1922 AD – Tilley patented the first commercially successful pressure lamp

The Standard Candle was defined in 1860... Candlepower definition and conversion factors

For financial reasons and to enable fair charges to be levied, some method of comparison of light output needed to be defined, and the result was the Standard Candle.

Defined in the Metropolitan Gas Act of 1860 as: “the light produced by a pure spermaceti candle weighing one-sixth of a pound (75g) and burning at a rate of 120 grains per hour (7.77g/h)”. Gas lighting burners were then rated as so many “candlepower”.

Later, in 1948 the SI unit of the was defined as “1/683 Watt per steradian at a wavelength of 555 nm”, and the Candela replaced the Standard Candle or Candlepower. The conversion factor is very close (0.981Cd = 1 C.P.) so for most purposes the Candlepower and the Candela can be considered interchangeable.

Modern lamps are rated in lumens. As there are 4π steradians in a sphere, and one Candela = 1 per steradian, then it follows that one Candela = 4π lumens or 12.57 lumens, making conversion possible between lamps rated in candlepower and lumens. One lumen equates to around 1.4 milliwatts of actual light power.

The main reason that gas, oil and electricity became popular was that they were all cheaper to operate than candles. Energy efficiency was a secondary consideration to cost, and as for carbon emissions and climate change, they had never been thought of!

We all think that the incandescent electric light bulb is an energy-wasting device.

We can’t wait to replace it with newer, more efficient lamps like Compact Fluorescents or LEDs.

But the incandescent lamp has been with us for over one hundred and thirty years... invented by Joseph Swan in 1878 and commercially perfected by Thomas Alva Edison in 1880. And apart from safely illuminating our Christmas trees ever since, it is a paragon of energy-efficient virtue compared with what was available before... candles, paraffin and gas lamps.

lm/W (primary energy) 6.000

5.000

4.000

3.000

lm/W (primary energy) 2.000

1.000

0.000 British Veritas Famos Tilley Gas mantle Tungsten Standard circular mantle pressure (single lamp 230 Candle wick lamp lamp mantle burner) volt lamp But... At just 5 lumens per Watt of primary energy, the incandescent light bulb is more correctly described as a heating appliance which emits a small proportion of light...

Just 0.75% of the primary energy used by a light bulb is converted into actual light! 99.25% is wasted as heat.

Newer technologies improve on this, but they’re still not perfect:

Current CFL: 3.8% efficient Future LEDs: 14.5% efficient? So we still have quite a long way to go to achieve truly efficient artificial lighting...... but we have come a very long way since the humble candle!

lm/W (primary energy) 120.000

100.000

80.000

60.000 lm/W (primary energy)

40.000

20.000

0.000 British Veritas Famos Tilley Gas mantle Tungsten Compact Ultimate LED Standard circular wick mantle lamp pressure (single lamp 230 volt fluorescent lamp Candle lamp mantle lamp burner) lamp 300lm/W Merry Christmas, everyone!