Experiment No.
1 Electric Lamps - Measurement of Illuminance
Aim: to determine the luminance of different lamps by lux meter.
Objective:
To perform the lighting levels, potential glare problem and energy efficiency of the lighting system of
various electric lamps like incandescent, compact fluorescent lamps by measuring luminance.
Theory:
illuminance measurements are the core of any lighting survey and the illuminance can be measured by a
portable instrument called a lightmeter or luxmeter. A luxmeter indicates the illuminance at the point of
measurement only, not the average in the space. To find the average illuminance in an area at the time,
it is necessary to divide the area into a number of equal areas which should be as nearly square as
possible. The illuminance at the centre of each square is then measured, and the results averaged.
The lumen method is the most widely used approach to the systematic design of electric lighting and it
can be used to estimate the average illumination on a working plane. The lux is a unit of measurement
of brightness, or more accurately, illuminance. It ultimately derives from the candela, the standard unit
of measurement for the power of light.
A lux meter works by using a photo cell to capture light. The meter then converts this light to an
electrical current. Measuring this current allows the device to calculate the lux value of the light it
captured.
The most common use of a lux meter is in photography and video filming. By measuring the light in
luxes, photographers can adjust their shutter speed and depth of field to get the best picture quality.
The device can also be very useful for filming outdoor scenes of television programs or movies as it
allows adjustments to make sure scenes filmed in different light levels have a consistent brightness on
screen.
Another common use of a lux meter is in meeting health and safety regulations. It can be used to check
whether the brightness of a room is enough to meet any rules designed to protect workers from
suffering damage to their eyesight. Using a lux meter takes into account the size of the room in a way
that simply measuring the intensity of the light source in lumens would not.
Inverse Square Law, General
Any point source which spreads its influence equally in all directions without a limit to its range will obey
the inverse square law. This comes from strictly geometrical considerations. The intensity of the
influence at any given radius r is the source strength divided by the area of the sphere. Being strictly
geometric in its origin, the inverse square law applies to diverse phenomena. Point sources of
gravitational force, electric field, light, sound or radiation obey the inverse square law. It is a subject of
continuing debate with a source such as a skunk on top of a flag pole.
Formulae Used:
I =E D2
Iaverage=¿
Ftotal=4 πIaverge
F total
Efficiency=
pss
Circuit Diagram:
Results:
Table:
Calculation:
Discussions:
At a methodological level, this work contributes with the presentation and the implementation of an
engine of rules that facilitates decision-making in an efficient way, telling users if the lighting complies
with the European standard and, in the case of deviation, indicating the value of this. Regarding the
hypotheses proposed previously, they can be answered thanks to the research performed in the study.
Distance between the light source and sensor: As the light energy spreads out away from the source the
area it covers is greater, meaning the intensity of the light decreases
The transparency of the transmission medium: any dust or gases in the air between the source and the
sensor could affect the intensity of light that reaches the sensor. The luminosity and size of source: the
luminosity is the energy that a radiation sources emits every second, the higher the luminosity, the
greater the light intensity. Background light: When measuring the light intensity there is bound to be
some background light that interferes with the reading and will change it slightly. Colour of source: If
the colour of the light is different than it means that the light will have a different wavelength or
amplitude. This would affect the intensity as a shorter wavelength (such as a violet wave) would have a
higher intensity.
Measuring Light intensity use the lux meter because it is the only one that uses a direct measurement of
light intensity.
Conclusion:
This study was intended to examine the luminance changes according to the altered distance to analyze
the relation between the targeted light source and the result using the instruments. From the
experiment in relation to the luminance changes according to the distance, the results show that the
difference in luminance value under the same conditions was around 5% when the point and surface
luminance meters were used. With the point luminance, there was a difference of around 3% as the
distance from the measured point increases by 1m. However, the impact of distance on surface
luminance was smaller compared to the one of point luminance. This study’s results imply that
luminance values vary according to the measurement distance. It can impact the luminance values.
Thus, it requires a reasonable standard on calculating the luminance under the “Act on Prevention of
Light Pollution caused by Artificial Lighting.
Recommendation:
