This document compares the light efficiencies of high intensity discharge (HID) lights and light emitting diodes (LEDs). It discusses the operation and characteristics of common HID light types including low-pressure sodium, high-pressure sodium, and metal halide lamps. It also describes the basic components and operation of LED lights. Tables provide data on the luminous efficacy, power conversion, lifetime, and illuminance of HID and LED light sources. The conclusion is that LED lights provide benefits over HID lights such as higher energy efficiency, longer lifetime, better color characteristics, and improved performance in dim lighting conditions.

1. Comparison of Light Efficiencies between High Intensity Discharge (HID) and Light Emitting Diodes (LED) Lights
Comparison of Light Efficiencies between High Intensity
Discharge (HID) and Light Emitting Diodes (LED) Lights
Mohammad Ismail Hazrati
Lecturer in Physics department, Education Faculty, Jawzjan University, Sheberghan, Afghanistan
Email: ismail.hazrati01@gmail.com
High intensity discharge (HID) lights have been widely used for indoor and outdoor lighting
applications. Light Emitting Diodes (LED) lights, which are fourth-generation light sources, have
recently appeared as an energy-efficient solution to indoor and outdoor lighting. LEDs are
semiconductors that emit light when electrical current runs through them. Comparison of LED
lights with HID lights can give more insight on the advantages of using LEDs in lighting
applications. based on the data available on various light sources, LED luminaires can be a
promising choice for lighting systems since they provide the advantages of energy efficiency,
longer life, good color characteristics, improved vision for mesopic conditions, lack of warm-up
time, compact size, directional light, reduced light pollution, environment-friendly characteristics,
dimming capabilities, and breakage and vibration resistance.
Keywords: Light efficiency, LED, High Intensity Discharge, Illuminance
INTRODUCTION
The increase in distribution and intensity of artificial lighting
worldwide has coincided with changes in the spectral
content of lighting. As they reach the end of their lifetime,
older street lights such as traditional orange high-pressure
sodium (HPS) and low-pressure sodium (LPS) lights are
being replaced with broad spectrum, high brightness
technologies such as light-emitting diodes (LEDs) and
ceramic metal halide lights (Gaston et al., 2013; Davies et
al., 2013; Frank, 1988). There are three types of lighting
sources that have been widely used for indoor and outdoor
lighting applications, including incandescent, fluorescent,
and high intensity discharge (HID) lights. The HID light
source family consists mainly of four members, including
mercury vapour (MV), low-pressure sodium (LPS), high
pressure sodium (HPS), and metal halide (MH) lights. The
generation of light is not the only purpose of HID lamps,
but it is the most visible application area of all lamps and
has an obvious effect on our quality of life. Nevertheless,
high-pressure discharge lamps are also used in many
other fields of application where electromagnetic radiation
in the UV and IR part is important.
Low-Pressure Sodium Lamp
In low-Pressure Sodium Lamp, electrons are accelerated
in an electric field and excite the sodium atoms. The
advantage of sodium is that the resonance lines (589.0
and 589.6 nm (sodium D-lines), corresponding to 2.1 eV)
are very close to the maximum of the sensitivity curve of
the human eye at 555 nm. With up to 40% conversion of
electrical power input into visible radiation, the luminous
efficacy can be up to 200 lm W−1. Nevertheless, since the
radiation power is concentrated to one single line, colors
cannot be distinguished under the light of a low-pressure
sodium lamp. However, contrasts between moving and
stationary objects are perceived faster under this
monochromatic light compared to illumination with other
(white) light sources (Meyer et al., 1988).
High-Pressure Sodium Lamp
An HPS lamp commonly consists of four basic
components, including a sealed, translucent, ceramic arc
tube, main electrodes, an outer bulb, and a base (Halonen
et al., 2010). The arc tube ceramic contains a mixture of a
small amount of xenon gas and sodium-mercury amalgam
and is used to provide a proper environment for producing
light. The xenon at a low pressure is used as a “starter gas”
in the HPS lamp. Lying at the coolest part of the lamp, the
sodium mercury amalgam provides the sodium-mercury
vapor that is needed to draw an arc. The main electrodes
are made of tungsten and carry a high-voltage, high-
Vol. 5(2), pp. 094-096, December, 2019. © www.premierpublishers.org. ISSN: 9098-7709
Review Article
Journal of Physics and Astronomy Research

2. Comparison of Light Efficiencies between High Intensity Discharge (HID) and Light Emitting Diodes (LED) Lights
Hazrati MI. 095
frequency pulse to strike the arc and vaporize the mercury
and sodium. The outer bulb, typically elliptical in shape and
made of hard glass, protects the arc tube from damage
and prevents oxidation of the internal parts. It also contains
a vacuum that reduces convection and heat losses from
the arc tube to maintain high efficacy. The lamp base is
typically a screwed base made of brass or nickel and
provides a socket for electrical connection. An HPS lamp
requires an inductive ballast to regulate the arc current flow
and deliver the proper voltage to the arc.
Metal Halide Lamp
Metal halide (MH) lamps can offer an excellent
combination of quality and performance. MH lamps not
only present more natural blue-white light compared to
HPS lamps, but also provide increased efficacy compared
to MV lamps. A standard MH lamp consists of four basic
components, including quartz arc tube, main electrodes,
outer bulb, and base. The operation of metal halide lamps
is similar to HPS lamps in that they produce light by way
of an arc tube contained within a glass bulb (LSC, 2017).
When an MH lamp is energized, the electric current passes
through the arc tube and ignites an electric arc through a
gaseous mixture of vaporized mercury and metal halides,
which are compounds of metals with bromine or iodine.
Similar to HPS lamps, inductive ballast is used to regulate
the current and the voltage to the lamp. The additional
metal atoms in the discharge have several advantages.
The visible lines emitted by the metals are often resonance
lines. Since resonance lines require the least energy to
become excited, the luminous efficacy increases. Another
advantage is the high voltage gradient due to the high-
pressure mercury (buffer) gas. This allows high electrical
power densities and small lamp currents.
High-Pressure Mercury Lamp
In a low-pressure mercury lamp with heavy particle
temperatures between 300 and 700 K and electron
temperatures above 10,000 K, the resonance lines of
mercury at 185.0 and 253.7 nm play a central role.
Increasing the pressure, the heavy particle temperature
approaches the electron temperature, both typically
between 4,000 and 11,000 K, depending on lamp current,
pressure, and position within the plasma. The mercury
discharges are very efficient at low pressures, emitting the
resonance lines at 185.0 and 253.7 nm, and at high
pressures, emitting spectral lines in the visible part of the
electromagnetic (Kettlitz and Grobjohann, 2002; Lister et
al., 2004).
LEDs, which are fourth-generation light sources, have
recently appeared as an energy-efficient solution to indoor
and outdoor lighting. They are semiconductors that emit
light when electrical current runs through them. While
LEDs have been used since the 1960s as indicator lamps
in consumer products, recent advancements have made
them practical for backlighting for cell phones, LCD
displays, automotive lighting, signals and street lighting
(Luo et al. 2009). The quality of LEDs has improved ten
times in the past decade, whereas the production cost of
LEDs has been reduced by around 90% (Xiaoyun,
Xiaojian, and Yan 2009). The major advantages of LEDs
are their low energy consumption, longer life span, good
color characteristics, improved performance in mesopic
vision conditions, instant on (no warm-up or re-strike time),
compact size, directional light, reduced light pollution,
environment-friendly characteristics, dimming capabilities,
breakage and vibration resistance, and improved
performance in cold temperatures.
The luminous efficacy of a light source is calculated by
dividing the total luminous flux of the light source by the
lamp wattage, expressed in lumens per watt. Luminaire
efficacy is computed by dividing the luminous flux of the
luminaire by the total power input to the luminaire, also
expressed in lumens per watt. The term “efficacy” is used
for these two parameters because they both have different
input (watt) and output (lumen) units. The term “efficiency”
is used when the input and output units are equal, so the
term “efficiency” is dimensionless. In simple terms,
luminous efficacy is how much light a light source
produces from a given amount of energy.
Table 1: Comparison of Heat Removal Mechanisms of
Different Light Sources (Arık et al. 2007)
Light Source Heat Lost
by
Radiation
(%)
Heat Lost
by
Convection
(%)
Heat Lost
by
Conduction
(%)
Incandescent >90 <5 <5
Fluorescent 40 40 20
High-Intensity
Discharge
>90 <5 <5
LED <5 <5 >90
Table 2: Comparison of Mercury, Metal Halide, and LED
Light Sources (Timinger and Ries 2008)
Mercury Metal Halide LED
Efficacy (lm/W) 50 110 80
Power (W) 50–1,000 20–250 2–15
Price/k lumen (€) <1.00 ~7.00 10.00–20.00
Lifetime (h) 10,000 22,000 50,000
Color White Cold white White
Efficient dimming Poor Poor Excellent
Table 3: Power Conversion of Metal Halide Lamps and
LEDs
Metal Halide Lamps LEDs
Visible light 27% 15–25%
Infrared 17% ~0%
Ultraviolet 19% 0%
Heat 37% 75–85%

3. Comparison of Light Efficiencies between High Intensity Discharge (HID) and Light Emitting Diodes (LED) Lights
J. Phys. Astron. Res. 096
Table 4: Illuminance Foot candle of HPS and LED light
sources
Illuminance Foot candle
Luminaire type Min Max
HPS 0.17 3.25
LED 0.15 3.67
According to biophysical studies, the human eye has two
different types of sensory cells known as cones and rods.
Cones are concentrated, in greater quantity, in the central
region of the retina (the fovea). These cells are responsible
for high luminosity visual response, when it’s possible to
distinguish the colors, the so-called photopic vision. On the
other hand, rods are responsible for vision at low
luminosity conditions (scotopic vision). This type of cell is
much more abundant than cones, being responsible for
perception under dim light, as well as bright and dark
differentiation. Under high luminance levels (above 3
cd/m2), the pupil dilation is small, so the image focusing
happens in the fovea region, where cone distribution
prevails. This characterizes the photopic condition of
vision. But when luminance gets lower (below 0.01 cd/m2),
the pupil dilation is greater and light is projected in a wide
retina region, thus sensitizing more rods than cones. This
effect implies on the scotopic visual response. In between
the photopic and scotopic conditions is the so-called
mesopic condition, which includes any intermediate
luminance level and is an interaction between both kinds
of sensory cells (Shreuder, 2008).
CONCLUSION
LEDs are fourth-generation light sources that have
recently appeared as an energy-efficient solution to
lighting. LEDs are semiconductors that emit light when
electrical current runs through them. An LED light consists
of LED chips, LED module, heat sink, optics, control circuit,
and power supply/driver. LED luminaires can be a
promising choice for lighting systems since they provide
the advantages of energy efficiency, longer life, good color
characteristics, improved vision for mesopic conditions,
lack of warm-up time, compact size, directional light,
reduced light pollution, environment-friendly
characteristics, dimming capabilities, and breakage and
vibration resistance. Comparison of LED lights with metal
halide and HPS lights can give more insight on the pros
and cons of using LEDs in lighting applications.
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Accepted 22 November 2019
Citation: Hazrati MI (2019). Comparison of Light
Efficiencies between High Intensity Discharge (HID) and
Light Emitting Diodes (LED) Lights. Journal of Physics and
Astronomy Research. 5(2): 094-096.
Copyright: © 2019. Hazrati MI. This is an open-access
article distributed under the terms of the Creative
Commons Attribution License, which permits unrestricted
use, distribution, and reproduction in any medium,
provided the original author and source are cited.