candescent Light Bulb Life Hours

The supply voltage is crucial, but contrary to a misconception, the turning off and often a light bulb plays little on his life.

How to increase the life expectancy of incandescent bulbs?

By reducing a little tension to their terminals. By reducing the voltage, reduced temperature, which significantly increases life expectancy.

By increasing the supply voltage (230V to 232.3V) + 1%, we get:

+ 3.4% of luminous flux (lumens)+1.6% of power consumed (+ 1.4% to + 1.55% according to other sources)+0.6% of current consumption (+ 0.4% to + 0.55% according to some other color temperature sources)+0.42% – 16% of life)))

(source: DealLEDLights “incandescent light bulb”)

+ 1% voltage made more 16% decrease the life expectancy of an incandescent bulb!

The life expectancy of an incandescent bulb is approximately doubled with 5% voltage and less (218.5V for 230V) but the brightness is also reduced by 17% (= 5×3.4) about.

Comparison in Economics: elasticity

These related changes are accurate locally around the nominal voltage. These are reports of related changes, so reports of two reports. This definition is to compare, in economics, elasticity (rated e) demand.

If the price increases by 1%, how many % varies the application?

Mathematical Note: logarithmic differential

It recognizes that the relative increase in power consumption is the sum of the relative increases of voltage (+ 1%) and current (+ 0.6%), which gives + 1.6% power. It is a reasoning about infinitesimal variations. The transformation of the product (P = IU) in short (or variations) is found by logarithmic differential.

Theory of radiation: Stefan’s law

Stefan Act gives the black body radiation. The total flux emitted (radiated) is proportional to the power fourth temperature.

This suggests that the relative variation of temperature of the black body is equal to 4 times the relative variation of flow emitted.

We use the approximation:

If we assimilate the filament of a light bulb filament to a theoretical black body, we get as a variation of power (absorbed electrically, so issued in the form of radiation) of 1.6% causes a variation in temperature of 1.6 / 4 = 0.4%. Here, the literature gives a variation of 0.42% in color temperature.

Temperature and color temperature are almost equal since we are in the case of a black body. The emitted light is related to the temperature (and the glass of the bulb, but it is not dyed).

In practice: diode in series

You can insert a diode in series with the light bulb. The current can no longer spend half of the time. The power consumed by the bulb is reduced by about 40% (not 50% as the filament is cold: his resistance is lower). The brightness is reduced by 70%. Light efficiency is reduced. This situation is interesting for incandescent bulbs in places difficult to access.

Under very reduced voltage (5V instead of 12V) halogen bulb filament

Start smoothly (softstart)

Little use. There are electronic components that reduce current to the ignition of the bulb (resistance NTC).

These resistances are worth 10 or 20 Ohms when cold lighting and drop a few ohms in operation (to hot).

In reality, this increases hardly the life expectancy of the incandescent light bulb. This helps reduce the current peaks, but the filament about to jump is already very worn. Hopefully a few % at the most.

Continuous feeding with voltage?

Quite possible if you have the same effective value. An alternative 230V bulb can be fed by a continuous 230V if there is such a source of tension. Similarly for halogen 12V bulbs who know the continuous 12V (cars), the 12V 50 Hz (ferromagnetic transformer) and effective 12V high frequency (electronic transformer).

Continuous feeding has the advantage of not vibrate the filament on the sector frequency. In some cases, this vibration can shorten the life of the bulb. However, this is rare.

Continuous feeding also has the advantage of not varying the temperature of the filament around its average temperature. It’s better that a filament to 2500 ° C continuously rather than alternate between 2400 and 2600 ° C. The loss of life to 2600 ° C is greater than the gain to 2400 ° C.

Gallery

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