Why LED?

In the last 10 years led technology ha enjoyed a technological boom, much like the gains made in solid state memory devices. In just the last 18 months white leds have doubled their luminous output from 50 lumens per watt to a 100 and over. Their colour has improved from a bluish white to a clean white, their cost has dramatically decreased, and are now finding many mainstream applications.
Indoor or household use a comparative study:

Technology Solid state lighting (LED) Cool White Incandescent Fluorescent 5–24 W Fluorescent 34 W (T12) Fluorescent 36 W (T8)
Luminous efficacy (lm/W) 100 16 45–60 50 up to 93
Lifetime (kh) 100 1 6-10 6-10 6-10
Hazardous substances No No Mercury Mercury Mercury
Mechanical Rugged will not break easily Glass Technology Glass Technology Glass Technology Glass Technology
On/Off Switching detoriate useful lifespan No Yes Yes Yes Yes
Color Rendering Index (CRI) >80 95 82 82 82

NOTES
HID lamps are not recommended for household and indoor use due to their low CRI Index; high pressure sodium lamp CRI 22, low pressure sodium lamp CRI 0.

LifeSpan
In all lightning technology except LED lightning, lifespan is defined as point of failure, i.e. the point where the light no longer works. In LED lightning lifespan of the led (usually stated between 50K and 100Khrs) is the point where the light output has only dropped by 30%

Outdoor use:

Technology Solid state lighting (LED) Cool White Incandescent Fluorescent high pressure sodium lamp low pressure sodium lamp
Luminous efficacy (lm/W) 100 16 45–93 39-140 100-160
Lifetime (kh) 100 1 6-10 24 16-30
Hazardous substances No No Mercury sodium sodium
Mechanical Rugged will not break easily Glass Technology Glass Technology Glass Technology Glass Technology
On/Off Switching detoriate useful lifespan No Yes Yes Yes Yes
Color Rendering Index (CRI) 70-93 95 40-90 20-40 20
Colour 4000K (Very close to Black body radiation curve in visable region) 2700K (Almost ideal to Black body radiation curve) but lots of power in IR region. 4200K (Very close to Black body radiation curve in visable region) 2200K (Bad Black body radiator) 2200K (Bad Black body radiator)
Dimmable Easy, PWM or current control Easy. However Triac chopper dimmers have been outlawed in many countries. Not Easy or not at all depending on light Not Easy or not at all depending on light and ballast Not Easy or not at all depending on light and ballast
Power Factor Easy to keep close to unity power factor (PF1) Easy to keep close to unity power factor (PF1) Easy to keep close to unity power factor (PF1) Not quite as easy to keep unity power factor (PF1) Not quite as easy to keep unity power factor (PF1)
Good lightning for reaction time, peripheral vision distance judgment Good Excellent Good Poor Poor
Power Applications Poor. Need to keep semiconductor junction tempreature below 125degC-145degC Good but not more then a few 100 Watts Good but not more then a few 100 Watts Excellent Kilo Watts can be achieved Excellent Kilo Watts can be achieved

Notes
When Scotopic/Photopic light calculations are used, it can been seen how inappropriate HPS lamps are for night lighting. White light sources have been shown to double driver peripheral vision and increase driver brake reaction time at least 25%. When S/P light calculations are used HPS lamp performance needs to reduced by a minimum value of 75%.

Scotopic vision is the monochromatic vision of the eye in dim light. Since cone cells are nonfunctional in low light, scotopic vision is produced exclusively through rod cells so therefore there is no colour perception. Scotopic vision occurs at luminance levels of 10-2 to 10-6 cd/m².

Mesopic vision occurs in intermediate lighting conditions (luminance level 10-2 to 1 cd/m²) and is effectively a combination of scotopic and photopic vision. This however gives inaccurate visual acuity and colour discrimination.

In normal light (luminance level 1 to 106 cd/m²), the vision of cone cells dominates and is photopic vision. There is good visual acuity (VA) and colour discrimination.

When examining costs it is important to assess the total lifecycle cost of a particular lightning application. WE ARE CURRENTLY DOING A STUDY TO EXAMINE PLAYBACK PERIODS, NPV, ROI FOR ALL THE LIGHTNING ABOVE. KEEP POSTED!