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LED Light Brightness, Lumens and Colour Temperature and Manufacturer Claims

Lumen Levels and Manufacturer Specifications

LED Chip vs LED Globe lumens. The measurement of luminous flux or lumens (Lm) is most commonly specified by LED bulb manufacturers but customers need to be careful to inquire whether the Lm measure is that of the actual LED chip provided by the manufacturer or that of the LED light bulb once the LED is placed inside the bulb housing.

For example, one of CREE’s (LED light manufacturer) latest chips is an XT-E LED chip which is rated as having a total luminous flux (Lm) of 780 Lm at approximately 7W or 1A which is a whopping 111 Lm/W. However,

(a) There are different bin numbers meaning that this type of chip at the lower end only has 87 Lm/W. Rarely do manufacturers use the highest possible Lm/W rating due to the increased cost of the chip.

(b) When the XT-E LED chip is inserted in the LED bulb the lumen output is further reduced due to the effects of current variations and losses from the LED lens, which amounts to a still reasonable but much lower 81 Lm/W, which is a loss of 27% over the original chip manufacturers specifications.

Therefore, with these technicalities and losses taken into account a luminaire or LED bulb which is rated at 780Lm in practicality only produces approximately 570 Lm.

LED Globe total luminous flux (lm) vs Zonal Lumens. Another area wich can be a cause for confusion is the measurement point whether the manufacturer is specifying the total luminous flux of the globe across 180° or specifying the zonal lumens or centre beam lumens or lumens within a certain angle. In such cases a globe with a narrower beam angle such as 35° will produce a higher centre beam lumens that a globe with a wide beam angle such as 60° just due to the different lens type. Yet the total luminous flux will be very similar. 

The important point here is to be weary of very high lumen values being quoted for narrow beam angle LED globes. 

Lumen Levels and Colour Temperature

Another factor which will affect lumen output is colour temperature such that warmer colours (yellow-white light) have inherently lower lumen output than cooler colours (white-blue light). See example below. Few LED light bulbs of 10W or lower will produce > 500 Lm. The 500 downward lumens represents the minimum cut off to qualify for most government programs. If you see much higher claims of > 500 Lm for bulbs of 3 to 10 W then you have reason to be suspicious of the retailers’ claims of total luminous flux. Some of the older 12W LED bulbs will also be less than 500 Lm whilst most bulbs in the range of 3-8W even today will produce less than 450 Lm.

CREE XTE 2800K Warm White = 450 Lm

CREE XTE 4000K Neutral White = 490 Lm

CREE XTE 5500K Cool White = 570 Lm

Summary and Conclusion

The moral of the story is to be weary of claims of high lumen outputs and whether the manufacturer or retailer is referring to warmer or cooler colour temperatures. Below is a guide of the typical lumens level which can be obtained at various power levels from more recent chip designs from various LED bulb manufacturers including our own.

 INSERT DIAGRAM HERE

References

Cree XLamp XT Family LEDs Binning & Labeling

next.gif LED Light Brightness - Lux and Lumen levels