1.3 LED Basic Parameters

Light Output

LEDs provide much higher light output on the same input power as comparable incandescent or fluorescent sources, because of their high efficiencies. This is also because the light emitted from the LED is naturally directional, and in almost all applications less light is lost in the fixture compared to traditional light sources. Colour quality is a key challenge facing LEDs as a light source for general lighting.


Various light sources versus LED, part 1:

Lamp Type Incandescent bulb Halogen lamp Metal halide lamp Mercury vapor lamp LED
  incandescent bulb Halogen lamp Metal halide lamp Mercury vapor light LED
Technical Incandescent bulb makes light by heating metal filament wire to light temperature until it glows. Halogen gas increases the lifetime of the wolfram filament and avoid the darkening of the bulb. The bulb can be operated on higher temperatures, which allows warmer CCT Adding rear earth metal salts to mercury vapor lamp enables high efficiency. It works on high pressure and temperatures, so special fixtures are required. The advantage is the compact size in comparison to fluorescents and incandescents lamps. Mixture of halides influences the CCT. After 10 000 hours the lumen output is approx. 83% of nominal. The outer bulb is coated with a phosphor for thermal insulation and converts some UV emissions into red light. After 2000 hours only 50% of nominal light output. Compact and highly durable light source enables both new designs and advantages in the light control. LEDs are switched on instantly and this makes applications with frequent switching easy. Tunable white  and RGB versions are already on the market. LEDs offer several benefits  which can be employed in combination with all well being applications.
Efficacy (lm/W) 6 - 16 16 - 30 75 - 125 40 - 75
80 - 140
Input power: (W) 20 - 60 55 - 100 20 - 24 000 50 - 500 0,2 - 100
Hazardous chemical content: no Halogens Argon, Mercury Argon, Mercury no*
Electronic ballast: no in general no needed to control the current needed needed
CRI: 100 100 70 - 95 40 - 60
65 - 97
Application: Indoor, outdoor Indoor applications like shops, residential Floodlight, outdoor, shops Outdoor applications, streetlights, facade Indoor, Outdoor
Additional information: high IR radiation high IR radiation High UV radiation High light pollution little UV and IR radiation
Lifetime: (hours) 1000 1000 - 3000 6000 - 20 000 4000 50 000
CCT: (K) 2700 2700 - 3500
3800 - 7000 3200 - 4200 2700 - 8000
Dimmable yes 
0 - 100%
yes
0 - 100%
yes
50 - 100%
no yes
5 - 100%

*LEDs have to be, as all semiconductor devices, disposed in a correct way, otherwise hazardous chemicals such as arsenic or phosphorus may occur.



Various light sources versus LED, part 2:

Lamp Type Compact fluorescent lamp - CFL Fluorescent lamp - FL Low pressure sodium - LPS High pressure sodium - HPS LED

CFL Fluorescent lamp Low pressure sodium lamp High pressure sodium lamp LED
Technical Light output decreases shortly after first use 5-10%, end of lifetime is approx. 70-80%. Full power is not reached after 1 second. The latest versions are CCFL (cold cathode). In general, for outdoor applications all FLs have problems at lower ambient temperatures, sometimes it is not possible to start lamp. The lamp reaches best efficacy if the temperature of lamp cold-spot is around 35°C. A problem is stroboscopic effect in some applications. Problems occur at lower ambient temperatures, sometimes it is not possible to start the lamp. After 25 000 hours lumen output decreases down to 50%. LPS lamps have an outer glass vacuum envelope around the inner discharge tube for thermal insulation. Yellow light is very insect maintenance friendly. The fact is the light source is quite spacious and the recycling process costs a lot of money. Practically, this type of the lamp is running out version because of low CRI. Smaller than LPS. Yellow light is very insect maintenance friendly. Compact and highly durable light source enables both new designs and advantages in the light control. LEDs are switched on instantly and this makes applications with frequent switching easy. Tunable white  and RGB versions are already on the market. LEDs offer several benefits  which can be employed in combination with all well being applications.
Efficacy (lm/W) 46 - 80
70 - 120 up to 200 100 - 150 80 - 140
Input power (W) 10 - 50 8 - 80 10 - 180
50 - 600 0,2 - 100
Hazardous chemical content Small amount of Mercury mercury, neon Sodium, Neon,
Argon
Sodium, Neon,
Argon, Mercury
no*
Electronic ballast needed or build in needed needed needed needed
CRI 80 - 90 80 - 99 30 25 - 85
65 - 97
Application Indoor applications Indoor Outdoor, streetlight, security Outdoor, streetlight, security Indoor, Outdoor
Additional information Frequently on/off reduce lifetime; high UV radiation Frequently on/off reduce lifetime; high UV radiation Full brightness rapidly; no lumen degradation over lifetime; relative big light source. Less light pollution as Mercury vapor lamps; Frequently on/off reduce lifetime little UV and IR radiation
Lifetime (hours) 15 000 15 000 - 45 000 16 000 - 23 000
10 000 - 24 000 50 000
CCT (K) 2700 - 5000 2700 - 8000 difficult to describe 2000 - 3000
2700 - 8000
Dimmable yes, 
3 - 100%, continues dim damage the light source
yes,
3 - 100%, continues dim damage the light source
no yes
50 - 100%
yes
5 - 100%

*LEDs have to be, as all semiconductor devices, disposed in a correct way, otherwise hazardous chemicals such as arsenic or phosphorus may occur.

Correlated Colour Temperature (CCT)

Did you know? CCT describes the relative colour appearance of a white light source, indicating whether it appears more yellow/gold or bluer, in terms of the range of available shades of white.

The most efficient (up to 140 lm/W) high-output white LEDs are phosphor-converted devices based on blue LEDs, characterized by very high CCTs of 5000K or above. Warm white (from 2700K to 4000K) devices are now available at efficacies comparable with FLs (up to 120 lm/W).

 
Kelvin color temperature scale chart  


Color Rendering Index (CRI)

CRI is a measure of the ability of a light source to render colors, relative to a reference light source (incandescent bulb). CRI may be compared only for light sources of equal CCTs.

 
Color rendering index  

 

 

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