In this experiment, you are going to learn how the light source intensity is changing by varying distance and angle of the detector.

Material

• Luxmeter
• Filament lamp
• Power supply
• Optical bench
• Slide mounts

Task 1

1. Estimate the dependence of the illuminance 'E' on the distance 'r' from the light source. 
2. Fix the light source with a holding mount on the optical bench
3. Connect the light source with power supply and let allow the light source to illuminate uniformly (~2 or 3 minutes)
4. The luxmeter must be calibrated before actually carrying out measurements. Possible background luminance must be determined with the lamp switched off and must be taken into account during evaluation.
5. Switch on the luxmeter and measure the background illuminance
6. Set the separation distance between the  luxmeter and light source at 0 degrees 
7. Measure the illuminance
8. Change the separation distance between the light source and luxmeter, measure Illuminance 
9. Repeat the same steps for other light sources

Task 2

1. Estimate the dependence of the illuminance 'E' on the angle of incidence 'φ'
2. Fix the light source with a holding mount on the optical bench
3. Connect the light source with power supply and let allow the light source to illuminate uniformly (~2 or 3 minutes)
4. The luxmeter must be calibrated before actually carrying out measurements. Possible background luminance must be determined with the lamp switched off and must be taken into account during evaluation.
5. Switch on the luxmeter and measure the background illuminance
6. Set the separation angle between the  luxmeter and light source at a fixed distance
7. Measure the illuminance
8. Change the separation angle between the light source and luxmeter, measure Illuminance 
9. Repeat the same steps for other light sources