What should you know before buying LED Bulbs (Part:3)

 (4) Color Rendering Index (CRI):

  • There are two standard measurements for the color characteristics of light: “color rendering index” (CRI) and “color temperature”, which expresses the color appearance of the light itself.
  • Color rendering index measures the ability of a light bulb to reproduce colors.
  • CRI is described How artificial light source is able to render the true color of objects as seen by natural outdoor sunlight which has a CRI of 100
  • The higher the CRI rating is, the better its color rendering ability.
  • Color Rendering Index (CRI) is a scale from 0 to 100.Incandescent bulbs are rated at 100 and most LED bulbs are usually rated somewhere between 80 and 85
  • CRI scoring of 100 is best and a CRI of zero being the worst.
  • CRI of 0: For a source like a low-pressure sodium vapor lamp, which is monochromatic compare to a source like an incandescent light bulb which has CRI of 100?
  • CRI of 62: A standard “cool white” fluorescent lamp will have a CRI near 62.
  • CRI of 70: Lamps with CRIs above 70 are typically used in office and living environments.
  • CRI of 82 to 86: Compact fluorescent lamps are graded at 82-86 CRI, which is considered high quality color rendering. CRI is a more important consideration for retail lighting design than it is for office lighting.
  • CRI of 80 and above: It is considered high and indicates that the source has good color properties.
  • Incandescent lamps and daylight have a CRI of 100, the highest possible CRI.
  • The higher the CRI of the light source, the “truer” it renders color.
  • The CRI can only be used to compare two light sources that have the same color temperature. A 5000 K, 80 CRI light source is not necessarily superior to a 4000 K, 70 CRI light source.
Color Rendering Index
Light source CRI
clear mercury 17
white deluxe mercury 45
warm white fluorescent tube 55
cool white fluorescent tube 65
deluxe warm white fluorescent 73
daylight fluorescent 79
metal halide 4200K 85
deluxe cool white fluorescent 86
metal halide 5400K 93
low pressure sodium 0-18
high pressure sodium 25
100-watt incandescent 100


Color Temperature & CRI
Lighting source Color Temperature Color Rendering Index
High Pressure Sodium Lamp 2100K 25
Incandescent Lamp 2700K 100
Tungsten Halogen Lamp 3200K 95
Tungsten Halogen Lamp 3200K 62
Clear Metal Halide Lamp 5500K 60
Natural Sun Light 5000K to 6000K 100
Day Light Bulb 6400K 80


Color Temperature & CRI
Kelvin Light Effect CCT CRI
Below 3600K Incandescent Fluorescent (IF) 2750 89
Below 3600K Deluxe warm white (WWX) 2900 82
Below 3600K Warm white (WW) 3000 52
3200K to 4000K White(W) 3450 57
3200K to 4000K Natural white (N) 3600 86
Above 4000 K Light white (LW) 4150 48
Above 4000 K Cool white (CW) 4200 62
Above 4000 K Daylight (D) 6300 76
Above 4000 K Deluxe Daylight (DX) 6500 88
Above 4000 K Sky white 8000 88

 (5) Beam angle:

  • How the light spreads out from the bulb (Beam Angle) is very important.
  • The beam angle determines how light is spread from the bulb into a given space.
  • The beam angle is the degree of width that light emanates from a light source. Specifically: The angle between those points on opposite sides of the beam axis where the intensity drops to 50% of maximum.
  • Typically a narrow beam angle is a ‘spot’ of light and called “Spot Light”. While a broader beam angle ‘floods’ with light, called a flood light. There are a number of much more specific designations of beam angle.
  • Beam angles of LEDs vary greatly and depend on their application. The shape of an LED bulb determines the direction light is emitted.
  • Narrow Spot Beam Angle: 05-15 degrees
  • Spot Beam Angle: 16-22 degrees
  • Narrow flood Beam Angle: 23-32 degrees
  • Flood Beam Angle: 33-45 degrees
  • Wide flood Beam Angle: 45+ degrees
  • Narrow angle bulbs less than 30 degrees are usually used when placing multiple down lights close to each other, such as in a hallway or when lighting cabinetry.
  • Larger beam angles are used with high-power LEDs for floodlighting. If you’re replacing incandescent or halogen lamps with LEDs, make sure the beam angle is similar to the old bulb.
  • Very large beam angles are sometimes found in pantries or walk-in wardrobes. As beam angle increases, we require more lumens (light output) to maintain the light’s intensity.


  (6) Efficacy (Lumen / Watt):

  • It is another important parameter to decide the performance of the LED bulb in terms of lumens.
  • It indicates effectiveness of the light bulb by converting electrical energy into visible light energy on watts used by Lighting Bulb; hence efficacy is total lumens per watt.
  • Example: 9W light bulb comes with lumens of 800 has an efficacy of 90 Lumens per Watt.
  • Incandescent bulbs give us light by passing electricity through a filament which heats up and emits light. In fact, 95% of the energy in these bulbs is lost to heat and only 5% is what produces light Hence, incandescent bulbs produce only 16 lumens / watt.
  • CFLs in the way they are built are more efficient and can give us between 50 to 70 lumens / watt (at least 3 times more than incandescent bulbs)
  • LED bulbs on the other hand, can output up to 100 lumens / watt – which make them one of the most efficient sources of lighting.
Parameter of LED Bulbs
Parameter Average Good Best
Lumens/Watt 75 90 100
Power Factor 0.7 0.8 0.9
CRI 60 70 80
LED Life in Hours 15000 25000 50000

 Other Technical Parameter:

(1) Instant Light:

  • LED Bulbs must be instant start and gives full Lumens from Starting.
  • When turning on CFLs and Fluorescent light bulbs, there is a slight hesitation before brightness is achieved, and some bulbs may flicker during warm up or even during operation.
  • Unlike fluorescents, LED bulbs, like incandescent bulbs, reach full illumination as soon as they are turned on.
  • LED lights produce a steady light which does not flicker.

(2) Dimming Capability:

  • Earlier versions of LED bulbs had the disadvantage of not being dimmable. Today, many LED bulbs are designed to work in dimmable switches which are provided in many lamps and home lighting fixtures.
  • Dimmable LEDs cost about 40% more than non-dimmable LEDs of similar wattage

(3) LED Driver:

  • The main cause of LED bulb failure is the driver. The driver is a small transformer that steps down the voltage from 230V AC to a much lower DC voltage for the LED.
  • It’s usually located inside the back of the bulb. A poor quality driver could result in bulb failure within months. The LED chip itself rarely fails until driver fails.

(4) LED Chip:

  • LED chips are manufactured by various big and small enterprises in the world. Some Good Suppliers make LED Chip of highest quality for longer life and more reliability.
  • Larger chip provide more lights, good stability against current variations, but it costs more.
  • Cheap and small led chip provides less light and stability. Ceramic COB lights are totally different in terms of size; they use multiple small chips to provide more lights and stability.

(5) Weight

  • LED lights need good heat dispassion, this can achieved by good amount of aluminum. Aluminum is generally used to provide better heat sink and extends the life of LED chip.
  • Thin heat sink can provide more area in less weight, but transfer enough heat for the removal.
  • Some lower quality products provide 12 to 20W lights in very low weight in plastic body. These products would not perform well even in small span of time.

(6) Heating:

  • Although LEDs don’t produce much heat they can overheat in operation if they’re not cooled correctly. Cheap LED’s are less efficient, produce more heat and are more heat sensitive. Operating above 60°C can damage cheaper LED’s shortening their life, reducing light output and efficiency. Generally the higher the wattage/power of a GU10 LED bulb, the more heat it produces requiring a more thermally efficient bulb body to keep the LEDs cool. Therefore beware of cheap higher wattage bulbs that don’t have a metallic or ceramic finned body. Another issue is that higher wattage thermally efficient LED bulbs may be so large that they are no longer a suitable size.

About Jignesh.Parmar
Jignesh Parmar has completed M.Tech (Power System Control), B.E(Electrical) from Gujarat University. He has more than 13 years experience in Power Transmission-Power Distribution-Electrical energy theft detection-Electrical Maintenance-Electrical Projects(Planning-Designing-coordination-Execution). He is Presently associate with one of the leading business group as a Deputy Manager at Ahmedabad,India. He is Freelancer Programmer of Advance Excel and design useful Excel Sheets of Electrical Engineering as per IS,NEC,IEC,IEEE codes. He is technical Author for "Electrical Mirror" and "Electrical India" Magazines. He is Technical Blogger and Familiar with English, Hindi, Gujarati, French languages. He wants to Share his experience & knowledge and help technical enthusiasts to find suitable solutions and updating themselves on various Engineering Topics.

5 Responses to What should you know before buying LED Bulbs (Part:3)

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