DHID (Digital HID) Vs. LED; Myths and Facts
When considering your lighting application solution, it is
prudent to educate yourself on the available lighting types on
the market today. Given the recent surge of promotion and the
popularity of LED lighting, many consumers assume LED to be the
solve-all for every lighting application. Although LED technology
meets and exceeds the standards for many applications, one should
be careful when considering LED for applications where light
projection or penetration is important; i.e. applications where
the light source is mounted at long distances from the target, as
in Street Lighting, High-bay Warehouse, Sports Arena, Airport and
Greenhouse lighting for example.
Facts about LED’s
- LED’s present many advantages over traditional light sources
including lower energy consumption, longer lifetime, improved
robustness, smaller size and faster switching. However, they are
relatively expensive and require more precise
current and heat management than traditional light sources.
- It should be noted that high-power (≥1W) LED’s are
necessary for practical general lighting
applications. Typical operating currents for these
devices begin at 350 mA.
- One of the highest efficiency ratings of high-power white
LED’s is claimed by Philips Lumileds Lighting Co., with a
luminous efficacy of 115 lm/W (350 mA). Please
note that these efficiencies are for the LED chip
only, held at low temperature in a lab. In a lighting
application, operating at higher temperature and with drive
circuit losses, efficiencies are much lower.
- Independent testing of commercial LED lamps designed to
replace incandescent or CFL lamps showed that average efficacy
was about 31 lm/W in 2008 and tested performance ranged from
4 lm/W to 62 lm/W) compared with 100-116 lm/W of
DHID lighting systems.
- Solid state devices such as LED’s are subject to very limited
wear and tear if operated at low currents and at low
temperatures. Many of the LED’s produced in the 1970s and 1980s
are still in service today. Typical lifetimes quoted are 25,000
to 100,000 hours but heat and current settings can extend
or shorten this time significantly.
As a leader and one source supplier of advanced lighting systems
for commercial and industrial lighting applications, including
DHID and specific LED lighting products, Accendo Electronics has
studied and field tested both LED and the next generation Digital
Ballast powered HID (called Digital HID or DHID) technologies for
applications requiring long light penetration and retained light
quality over extended time periods. In our research, we uncovered
key myths and facts about LED’s you should consider when deciding
on your project lighting.
Myth: LED Lighting Life
Expectancy is 100,000 Hours Plus
False!
Manufacturers claim mean time before failure (MTBF) ratings on
LED’s to be 50,000 hours to 100,000 hours or more. Although in
cases LED’s do meet these extended MTBF specifications, this
number must be directly correlated to the LED application itself.
Factors such as mounting distance, the lumens per Watt (lm/W)
rating, and operating temperature all contribute to the reduction
of the LED’s MTBF. Realistically, LED’s used for street lighting,
or high-bay warehouse applications for example, may be considered
to be failed at 30,000 hours or sooner due to
the significant light diminishment incurred in the time stages of
the LED’s operation.
The most common symptom of LED (and diode laser) failure is the
gradual lowering of light output and loss of efficiency. Sudden
failures, although rare, can occur as well. Early red LED’s were
notable for their short lifetime. With the development of high
power LED’s, the devices are subjected to higher junction
temperatures and higher current densities than traditional
devices. This causes stress on the material and may cause early
light output degradation. To quantitatively classify lifetime in
a standardized manner it has been suggested to use the terms L75
and L50 which is the time it will take a given LED to reach 75%
and 50% light output respectively. L50 is equivalent to the
half-life of the LED.
Facts:
- The LED light quality diminishes or dims
over the operating lifetime of the LED bulb. This degradation in
light should be considered when reviewing the MTBF of LED’s since
the light emitted at the LED’s life start is not equal to the
light emitted at the bulbs half-life or life-end. If the LED bulb
cannot produce the light output originally specified, it is a
form of failure.
- Over time, heat created by LED’s also has an adverse
effect on the systems light quality and MTBF. Depending
on the class of the LED bulb used, factors such as powder coating
(filter) degradation and the material used to manufacture the LED
lens, further add to the truism that LED’s do not necessarily
meet their manufacturer’s specified MTBF ratings and lighting
quality claims.
-
DHID equals or outperforms the longevity of
LED in most industrial and commercial applications at
lower costs. The integrated microprocessor of the DHID doubles
the life expectancy of the HID lamp by maintaining full level
of illumination up to 28,000 – 30,000 hours.
- Studies have proven that DHID used as a direct replacement
and mounted at the same distance as the original HID lighting,
outperforms LED in many quantifiable measurements of
energy efficiency and light penetration. DHID offers a
market leading lumens per Watt rating of 114 lm/W – 118 lm/W
(which is 25% – 30% above LED’s lm/W rating) and therefore
delivers higher energy efficiency, greater light penetration, and
quality light up until its 30,000 hours MTBF; and all for a
fraction of the cost of LED.
Myth: LED’s Project/Penetrate Light at Long
Distances
False!
Our studies proved that LED’s are not well suited for
projecting light efficiently at distances exceeding 15ft (4.5m
approx.).
Facts:
- At a typical street light height mounting distance of
approximately 32.8ft (10m), the foot-candle (fc) measurements of
the light emitted from both LED and DHID were recorded at the
ground:
-100W LED street light produced 0.75 foot-candles
-70W DHID with a 70W Ceramic Metal Halide (CMH)
lamp produced 1.75 foot-candles
- For street lighting applications the high lumens per Watt
rating of DHID provides the best value
delivering higher energy efficiency, greater light penetration,
and quality of light over time.
Where to Use LED Fixtures
- Industrial and commercial applications where useful light
penetration would not exceed 7 – 8 meters such as commercial room
lighting, exit signs, target illumination in retail stores and
others.
- Flash lights, and other utility lighting.
- Instrument panel lights and other back lighting applications.
- Industrial and architectural back lighting, and other
decorative applications.
Why DHID (Digital HID) is Preferred for Street Lighting
and High-bay Lighting Projects
When selecting a lighting system, significant consideration
should be given to the performance, cost, and life expectancy of
both solutions. Given the poorer lumens per Watt rating, high
initial expense and realistic wear data of LED’s, we determined
the DHID solution to be the better value.
- Progressively thinking end-users agree that DHID is the more
robust lighting solution with value added benefits not offered by
LED; initial cost of investment, longer range of light
penetration, and low maintenance costs were noted.
- With CMH or HPS lamps, the end-user can expect brighter light
at the ground, with 30,000 hours of life expectancy and less than
5% degradation in light quality/brightness over the lifetime of
the bulb. When a DHID system CMH bulb fails, only the bulb itself
needs to be replaced making it a most cost-effective alternative
to expensive LED replacements.
- Maintenance and control of a DHID lighting systems is further
simplified by Accendo’s Light Control Software
which provides real-time tracking and performance data of each
DHID light via radio frequency (RF) communication.
Accendo Embraces the Use of LED’s for the Following
Applications:
- Wall packs and canapé light fixtures (currently under
development).
- Panel lights for architectural and special purpose lighting
applications (currently under development).
- Exit signs.
We welcome the opportunity to discuss our findings with you
further. As confirmation of Accendo’s proven product
specifications, Risk Free Trial units are now available
for your own 30 day evaluation. Accendo Electronics is committed
to the success of your lighting application; please do not
hesitate to contact us for additional information today.
Anthony Borges
aborges@accendoelectronics.com
www.AccendoElectronics.com
