The working principle of HID lamp and LED are different, the light spectrums of them are different, both of them have advantages and disadvantages, let's check of them deeper and understanding better.

1. HID VS LED
HID Working Principle:
High-intensity discharge lamps (HID lamps) are a type of electrical gas-discharge lamp which
produces light by means of an electric arc between tungsten electrodes housed inside a
translucent or transparent fused quartz or fused alumina arc tube. This tube is filled with noble
gas and often also contains suitable metal or metal salts. The noble gas enables the arc's
initial strike. Once the arc is started, it heats and evaporates the metallic admixture. Its
presence in the arc plasma greatly increases the intensity of visible light produced by the arc
for a given power input, as the metals have many emission spectral lines in the visible part of
the spectrum. High-intensity discharge lamps are a type of arc lamp.
HID lamp including:
 Sodium-vapor lamps
 XED lights (Xenon Energe Saving Discharging Lamp)
 Metal-halide (MH) lamps
 Mercury-vapor lamps

2. LED Working Principle:
A light-emitting diode (LED) is a semiconductor light source that emits light when current
flows through it. Electrons in the semiconductor recombine with electron holes, releasing
energy in the form of photons. The color of the light (corresponding to the energy of the
photons) is determined by the energy required for electrons to cross the band gap of the
semiconductor. White light is obtained by using multiple semiconductors or a layer of light-
emitting phosphor on the semiconductor device.
A basic LED light source is a semiconductor diode with a p region and an n region. When the
LED is forward biased, current flows through the LED. As current flows through the LED, the
junction where the p and n regions meet emits random photons. LEDs emitting in the window
of 820 to 870 nm are usually gallium aluminum arsenide (GaAIAs). Laser is also a
semiconductor diode with a p and an n region like LED, but it provides stimulated emission
rather than the simplex spontaneous emission of LEDs. The main difference between a LED
and a laser is that the laser has an optical cavity required for lasting. The cavity is formed by
cleaving the opposite end of the chip to form highly parallel, reflective, mirror-like finishes.

3. HID Lights Spectrum VS LED Light Spectrum:
All HID lights with full spectrum of visible light (Red, Orange, Yellow, Green, Blue, Indigo,
Volet), UV and infrared spectrum; LED light spectrum is combined with blue, green and red
LED, LED does not have UV nor infrared spectrum.

4. Real Light Effect Comparision:
When we use camera take videos of flowers under HID lights and LED lights, we find that
there is no flickering with HID lights, and there is serious flickering with LED.
Real Projects comparision:
 HID lights dot not have glare VS LED with serious glare problem.
Because LED working principle is similar with laser, it also creats very serious glare
problem, for outdoor Lighting, when there is glare along streets, the drivers eyes will be
blinded by glares and can not see objects, it is very dangerous and easy to cause
accidents; disability glare impairs the vision of objects.This could arise for instance when
driving westward at sunset. Disability glare is often caused by the inter-reflection of light within
the eyebal, reducing the contrast between task and glare source to the point where
the task cannot be distinguished. When glare is so intense that vision is completely impaired,
it is sometimes called dazzle.

5.  HID Lights spectrums do not have blue light damage or pollution problem, cool
white LED serious blue light can make damage of human being eyes, and make
pollution for environment.
Because the CRI and light efficiency of low CCT LED is low, to make the LED looks white
with higher CRI and lm/watt, most of LED manufactories increase the blue light-emitting
diodes (LEDs) proportion, but these LED can cause serious damages for human eyes and for
environment.
The fact that blue light penetrates all the way to the retina 'the inner lining of the back of the
eye' is important, because laboratory studies have shown that too much exposure to blue light
can damage light-sensitive cells in the retina. This causes changes that resemble those of
macular degeneratio, which can lead to permanent vision loss.
Blue light can mislead the migration of birds, causing large numbers of bird deaths; Blue light
apparently suppresses the production of melation which helps you sleep at night. And it’s not
just humans whose circadian rhythms are getting messed up — the effects are seen
throughout the animal kingdom; In rainy or foggy days, if both sides of the road are equipped
with LED lights, our vision in front of the car is very blurred, which is very easy to cause traffic
accidents.XED Lights without above problems, offer safer and more environmental friendly
solution for street lighting.

6.  Real Effective Lifetime and Failure Rate:
The mercury and metal halide lifetime of HID lamp is still short at present, several sousand
hours; but the real effective lifetime of XED light and HPS is super long now, lumen loss <30%
at 30,000hours; LED theory lifetime is 50,000hours or 10,000hours, but that is not real
effective lifetime, lots LED light go dim or fail after installed 2 year, 1 year or even several
months. so real lifetime of XED and HPS HID lamps are much longer than LED.

7.  Maintainence Differences:
HID hardware normally including separate HID ballast, HID bulb and HID fixture, if there is
one of the part failed, just replace bulb or ballast is ok, normally fixture not easy fail; Well if
there is any part LED failed and cause the whole LED can not work, normally should use a
new LED light to replace a old one, the cost is higher; and because of LED failure rate is
higher, the cost of new light, replacing labour cost and the costs of hiring lifts, finally LED
maintenance costs are much higher than HID.

8.  Applications:
From above comparision including glare, CRI., blue light damage and real lighting effects
factors, we can easyly find that HID lights are much better for big power indoor and outdoor
lighting projects, but there is disadvantages of HID lights, that HID can not be made to small
power model like 3W~50Watt, but LED can make small power bulbs, in this case, it is better
to choose low CCT warm color LED for lighting to avoid blue light damage.