Experiment No.: 1
Experiment Name:
To Determine Illumination of a Surface for a Drawing Room by Means of Lux Meter
Objective:
To measure the intensity of light with lux meter of (i) fluorescent lamp (ii) compact fluorescent lamp (CFL).
Theory:
Lux meter (Light Meter): The meter or light meter measure illumination in terms of luxes(lx) or foot candles (fc). A lux is equal to the total intensity of light that falls on a one square meter surface that is one foot away from the point of source of light. A foot candle is equal to the total intensity of light that falls on a one square foot surface that is one foot away from the point source of light. Most lux meter or light meter consist of a body, photocell or light sensor, and display. The light that falls on to the photocell or sensor contains energy that is converted to electric current. In turn, the amount of current depends on the amount of light that strokes the photo cell or light sensor. Lux meter read the electrical current, calculate the appropriate value, and output the results to an analogy digital video display. Since light usually contains different colours at different wave lengths, the reading represent the combined effects of all the wave lengths. Typically standard colours or colours temperatures are expressed in degree kelvin (K). The standard colour temperature for the calibration of most lux meters is 28560K, an amount that is more yellow than pure white.
Selecting lux meters or light meters requires certain performance specifications include photo cell, illumination range. Lux resolution, operating temperature and foot candle resolution.
Analog devices display values on a dial usually with a needle or pointer. Digital devices display values as number letters. Lux meter may be portable or designed to sit atop a desk.
Lux meter are used to measure levels of light in schools, hospitals, production areas and laboratories. They are also use to monitor light sensitive display in museums, art gallery etc., special features include backlit display, low battery indicators, low voltage alarms, built in memory. Auto power off zero function.
Apparatus Used:
| Sl No. | Name of Apparatus | Quantity | Specification | Makers name |
| 1. | Lux Meter | 1 | 0-50000 Lux Digital | Waco |
| 2. | Measuring Tape | 1 | 3 m | Basik |
| 3. | Fluorescent Lamp (Double and Single) | 2 | 36 W (Single) 72 W (Double) | Philips |
Pictorial Representation:
Block Diagram of Luxmeter :
Observation table:
| Sl no | Types of lamp | Distance (m) | Light intensity, I (lux) |
| 1. | Flourescent Lamp | 1.6 | 190 |
| 2. | 1.5 | 211 | |
| 3. | 1.4 | 252 | |
| 4. | 1.1 | 330 | |
| 5. | 0.9 | 405 | |
| 6. | 0.7 | 550 |
Graph:
Remarks:
For this experiment a dark rom is needed, but in our college, there is no such arrangement is available. So that is why, the result of the experiment includes some error.
