Highschool electronics- Illumination

[physics_bro]

Homework Statement

I have done an experiment at school, where the voltage drop across an LDR was measured at varying light intensities. The light intensity was determined by the distance of a light globe from the LDR (the light globe was part of an external circuit). Also the current flowing through the LDR circuit was measured at each distance.

Bacically I have voltage drop across LDR, current in circuit, distance of globe from ldr and resistance of LDR using ohm's law.
oh yeh and i have the wattage of the globe and its supply voltage
Is it possible to calulate the light intensity in lux by using an equation or did this have to be measured using a lux meter?

I realize the distance of the light globe from the LDR is effectively the light intensity, but i need it to be in lux...

Homework Equations

The Attempt at a Solution

 

[andrevdh]

This is the age old problem of calibrating an instrument. Meaning that you have to draw a calibration curve of illumination in lux against the resistance of you device.

This can either be done with sources of known illumination (not a recommended procedure) or using another measurement device that will give you the readings in lux (not very helpfull is it!).

Try and borrow a lux meter from a photographer to calibrate your resistor.

 

[m2003]

I commend you for conducting an experiment to explore the relationship between light intensity and voltage drop across an LDR. It is important to understand the principles of illumination and how external factors, such as distance and current, can affect it.

To answer your question, it is possible to calculate the light intensity in lux using an equation. Lux is a unit of measurement for illuminance, which is the amount of light that falls on a surface. It is defined as one lumen per square meter (lm/m^2). In order to calculate the light intensity in lux, you will need to know the luminous flux (in lumens) of the light source and the area (in square meters) on which the light is falling.

The equation for calculating light intensity in lux is:

lux = lumens/area

In your experiment, the luminous flux can be determined by multiplying the wattage of the light globe by its efficacy (lumens per watt). The area can be calculated by multiplying the distance between the light globe and the LDR by the surface area of the LDR. By plugging in these values, you should be able to calculate the light intensity in lux.

However, it is always recommended to use a lux meter for accurate measurements. This is because the relationship between distance and light intensity is not always linear, and external factors such as ambient light can affect the readings. A lux meter is specifically designed to measure light intensity and will provide more accurate results.

In conclusion, while it is possible to calculate light intensity in lux using an equation, it is always best to use a lux meter for accurate measurements. Keep up the good work in your exploration of electronics and illumination!