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Light measuring engineering

Approximately 80% of allsensations are experienced by theeye. Light is required for thispurpose. 25% of human energy isneeded for the seeing process.

The light parameter

Humans are day beings, i.e. we areused to a light intensity such asthat which is available during theday. Values lie between approx.5000 Lux on a dull Winter´s dayand approx. 100 000 Lux on asunny Summer´s day.

The light intensity of artificial lightsis usually between 100 and 1000 Lux.

Sunny Summer´s dayoutside Approx. 100 000 Lux

Overcast skyin Summer Approx. 20 000 Lux

Sunny Winter´s dayoutside Approx. 10 000 Lux

Dull Winter´s dayApprox. 3 000 Lux

Good workplace lighting1 000 Lux

Good street lighting 40 Lux

Full moon 0.25 Lux

Starlight 0.01 Lux

Light intensities:

Fatigue on account of too little lightoccurs more in the organism as awhole than in the eye itself. For thisreason insufficient or bad lightingconditions cannot be identified asthe cause of accidents or fatigue.

According to the documentationavailable approx. 30% of allaccidents result directly orindirectly from inadequate lighting.In the interest of accidentprevention it is imperative thatresearch is done in this area.

Different light intensities arerecommended by standards bodies,depending on the task. Lightintensities of approx. 100 to 250Lux are sufficient for simple tasks. A minimum of 1000 Lux is requiredfor precision work.

A light intensity measuringinstrument must be able toreconstruct exactly theresponse of the human eye.This is achieved by specialoptic filters. A specialmeasuring cell (photo diode)converts the incident lightinto an electric signal whichis then shown.

Effects

green yellow

blue red

UVlight infrared

Wavelength

Sens

itivi

ty

400

500

600

700

800

1.00

0.90

0.80

0.70

0.60

0.50

0.40

0.30

0.20

0.100.00

Unit: LuxLight intensity is the ratio of the lightflux on an area to the area.

Light intensity (Lux) =light flux (lm)area (m2)

E = ΦA

Spectral response of the eye:

Light is made up of very highelectromagnetic oscillation between380 and 770 nm. They areexperienced by the eye as light.

Light intensity:

Examples of lightintensities:

Light flux:

Unit: 1 lumen (lm)Light flux is the total radiationpower emitted from a light sourceand photometrically assessed.

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