A three-way bulb uses 50,100, or 150 W of electrical power to deliver 665,1620, or 2285 lm in it

step 1 Okay, so we have a light bulb with three different power settings of 50 watts, 100 watts, or 150

A three-way bulb uses 50,100, or 150 W of electrical power...

A three-way bulb uses $50,100,$ or $150 \mathrm{W}$ of electrical power to deliver $665,1620,$ or $2285 \mathrm{lm}$ in its three settings. The bulb is placed $80 \mathrm{cm}$ above a sheet of paper. If an illumination of at least $175 \mathrm{lx}$ is needed on the paper, what is the minimum setting that should be used?

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Key Concepts

Luminous Flux

Luminous flux is a measure of the total amount of visible light emitted by a source, measured in lumens. It quantifies the perceived power of light, taking into account the sensitivity of the human eye, and is used to compare the brightness of different light sources.

Illuminance

Illuminance is the measure of the amount of light arriving on a surface per unit area, expressed in lux. It defines how bright the light appears on a surface and is calculated by dividing the luminous flux by the area over which the light is distributed.

Inverse Square Law

The inverse square law explains how the illuminance from a point light source decreases with increasing distance. Specifically, as the distance from the light source is doubled, the illuminance falls by a factor of four, since light spreads over an area proportional to the square of the distance.

Point Source Approximation

The point source approximation assumes that a light source emits light uniformly in all directions from a single point. This simplification allows the use of the inverse square law to estimate the illuminance on a surface at a given distance from the light source.

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