26
A. Funde and A. Shah
Fig. 2.7 Comparison of the intensity of sunlight through window glass with the light intensity from
manufactured lamps. The spectral irradiance of artificial lamps is very small in comparison with
the sunlight that we receive indoors through a window glass [9]
without the need for changing pre-existing infrastructures. These applications can
function on their own with a less intense indoor light originating either from sunlight
through the window, or from artificial indoor light sources.
Indoor lighting by artificial lamps is very weak in intensity, typically 200 times
less than sunlight entering though window glass, as shown in Fig. 2.7. It is very
much weaker than direct sunlight, as was depicted in Fig. 2.1. The spectral nature of
artificial light sources is depicted in Fig. 2.8.
Note that in all museums, halogen lamps are used, and not LEDs, because the
spectral irradiance curve of a halogen lamp comes, in its form, nearest to the spectral
irradiance curve of the sun, whereas the spectral irradiance curves of LEDs have a
totally different form. Thus, if we illuminate a painting with a halogen lamp, the
colours of the painting are rendered correctly—whereas this is not at all the case
if the painting would be illuminated by LEDs. One could even argue that halogen
lamps are best suited for all situations, like reading, where good lighting and comfort
are important, as the human eye is genetically adapted to sunlight, and halogen lamps
imitate sunlight better than LEDs.
5
Solar Cell Applications of Indoor Light
There are a large variety of applications, where solar cells are used under indoor
conditions. This is the case of most pocket calculators, which are generally fitted
with amorphous silicon solar cells, and are destined to work even at very low light
intensities. In fact, we would expect our calculator to work if the illumination level
5 There have been investigations (albeit controversial ones), which claim that very intense LED lights
are harmful to the eye and lead to macular degeneration. Given that lighting generally accounts for
less than 5% of Electricity Consumption, the authors hold that it is basically unjustified to prohibit,
in the EU and in Switzerland, in the near future, the sales of all incandescent lamps, including
halogen lamps, in the name of Energy Saving.
A. Funde and A. Shah
Fig. 2.7 Comparison of the intensity of sunlight through window glass with the light intensity from
manufactured lamps. The spectral irradiance of artificial lamps is very small in comparison with
the sunlight that we receive indoors through a window glass [9]
without the need for changing pre-existing infrastructures. These applications can
function on their own with a less intense indoor light originating either from sunlight
through the window, or from artificial indoor light sources.
Indoor lighting by artificial lamps is very weak in intensity, typically 200 times
less than sunlight entering though window glass, as shown in Fig. 2.7. It is very
much weaker than direct sunlight, as was depicted in Fig. 2.1. The spectral nature of
artificial light sources is depicted in Fig. 2.8.
Note that in all museums, halogen lamps are used, and not LEDs, because the
spectral irradiance curve of a halogen lamp comes, in its form, nearest to the spectral
irradiance curve of the sun, whereas the spectral irradiance curves of LEDs have a
totally different form. Thus, if we illuminate a painting with a halogen lamp, the
colours of the painting are rendered correctly—whereas this is not at all the case
if the painting would be illuminated by LEDs. One could even argue that halogen
lamps are best suited for all situations, like reading, where good lighting and comfort
are important, as the human eye is genetically adapted to sunlight, and halogen lamps
imitate sunlight better than LEDs.
5
Solar Cell Applications of Indoor Light
There are a large variety of applications, where solar cells are used under indoor
conditions. This is the case of most pocket calculators, which are generally fitted
with amorphous silicon solar cells, and are destined to work even at very low light
intensities. In fact, we would expect our calculator to work if the illumination level
5 There have been investigations (albeit controversial ones), which claim that very intense LED lights
are harmful to the eye and lead to macular degeneration. Given that lighting generally accounts for
less than 5% of Electricity Consumption, the authors hold that it is basically unjustified to prohibit,
in the EU and in Switzerland, in the near future, the sales of all incandescent lamps, including
halogen lamps, in the name of Energy Saving.