Light Sensor

 Experiment Guide

   

Light Sensor

Introduction:

Part of the Eisco series of hand held sensors, the light sensor allows students to record and graph data in experiments on the go.

This sensor is very versatile with applications in many areas of the natural sciences. It can be used to study photosynthesis in biology, light-emitting chemical reactions in chemistry, the effect of changing voltage on a light-bulb’s output in physics and more. This sensor measures illumination with three ranges; it can be used in low light environments such as in a classroom, or high light environments as in daylight outdoors. With both fast and slow modes, it can be used to measure fast light changes such as those produced by light bulbs connected to an AC supply, as well as the almost steady levels outside on a sunny day.

Sensor Specs:

Range 0-1000 lux | 1 lx resolution | 3000 max sample rate Range 0-6000 lux | 1 lx resolution | 3000 max sample rate Range 0-150000 lux | 6 lx resolution | 3000 max sample rate

ACTIVITY – Color Dependent Reflectivity of Light

General Background:

The amount of light reflected from various surfaces depends on many factors, including the type of material and the color of the surface. Light that is not reflected off of a surface is absorbed as heat in the material. One may think of a variety of useful reasons for determining the best colors of objects based upon their reflectivity, such as keeping the interior of a house or vehicle cool.

In this activity, you will measure the amount of reflected light off a variety of color surfaces to determine how color affects the percent reflectivity. You will calculate the percent reflectivity of each color surface using the following equation:

%  𝑟𝑒𝑓𝑙𝑒𝑐𝑡𝑖𝑣𝑖𝑡𝑦 =  𝑎𝑚𝑜𝑢𝑛𝑡  𝑜𝑓  𝑙𝑖𝑔ℎ𝑡  𝑓𝑟𝑜𝑚  𝑠𝑎𝑚𝑝𝑙𝑒  𝑠𝑞𝑢𝑎𝑟𝑒𝑎𝑚𝑜𝑢𝑛𝑡  𝑜𝑓  𝑙𝑖𝑔ℎ𝑡  𝑓𝑟𝑜𝑚  𝑎𝑙𝑢𝑚𝑖𝑛𝑢𝑚

 ×  100

This value will give the percent reflectivity of each surface in proportion to a highly reflective material.

Required Materials:

Eisco Light Sensor & Handheld Unit 2 - Eisco Metalware Sets (base retort stand, rod, clamp with bosshead) [MS-ST1] Eisco Light Box and Optical Set [PH0615] Eisco Battery Eliminator [PH0971A] 2 - 4mm connecting leads Aluminum foil Black cardboard paper

Procedure

1. Assemble the apparatus as shown in Figure A. Using a clamp attached to a base retort stand, situate the lamp 10 cm above the surface of a table pointing downwards. Using the 4mm banana plug cords, plug the lamp into a power supply of 9-12 V. Insert the wide slit cover into the lamp side of the light box.

Figure A

2. Set the Eisco Light Sensor to detect in the range 0-6000 lux. 3. Using a second base retort stand, situate the Eisco light sensor such that the

sensor points at the region directly beneath the light box. The sensor should be positioned about 5 cm above the surface of the table, and pointing at about a 45° angle with respect to the surface. Block as little light from the light box as possible with the body of the sensor unit.

4. Place the square of aluminum on the table directly under the light source. Record the amount of light the sensor receives in lux in the table below. The room lights should be turned off during data collection.

5. Replace the aluminum square with a white square, the black square, and each of the other color squares included in the optics kit to measure the amount of reflection for each square. Record in the data table. For the white square, the reverse side of one of the color cards may be used. Be sure to not disturb the position of either the light box or light sensor during measurement.

Data Table

Color/ Material

Aluminum White Black Purple Yellow Orange

Light (Lux)

% Reflectivity

100%

Color/

Material Red Pink Blue Green Violet

Light (Lux)

% Reflectivity

Analysis

1. Using the formula given above, calculate the percent reflectivity for each of the different color surfaces measured. Show at least one calculation. The percent reflectivity in this activity is given in proportion to aluminum, so we assume that the aluminum square is 100% reflective.

2. What squares were most reflective? Which squares were least reflective? 3. What color vehicle would you want to paint your car to keep it coolest in the

summer? What is the best color for the roof of your house to keep it warm in the winter?

Sample Results

Color/

Material Aluminum White Black Purple Yellow Orange

Light (Lux) 130 30 0 8 33 35

% Reflectivity

100% 23.1% 0.0% 6.2% 25.4% 26.9%

Color/

Material Red Pink Blue Green Violet

Light (Lux) 26 24 20 14 18

% Reflectivity

20% 18.5% 15.4% 10.8% 13.8%

Answers to Questions

1. %  𝑟𝑒𝑓𝑙𝑒𝑐𝑡𝑖𝑣𝑖𝑡𝑦 =   !"#$%&  !"  !"#!!  !"#$  !"#$%&  !"#$%&!"#$%&  !"  !"#!!  !"#$  !"#$%&#$

 ×  100   so for the white square,

%  𝑟𝑒𝑓𝑙𝑒𝑐𝑡𝑖𝑣𝑖𝑡𝑦 =  30130

 ×  100 = 23.1% 2. The white square, and the lighter colors (yellow, orange, red, pink) had

highest reflectivity. The darker colors (purple, green, violet) had lower reflectivity. The black square did not reflect at all.

3. A white car, or one of the other lighter colors would keep a car coolest. A black roof will absorb the most heat from the Sun.