LED luminous efficacy (lumens per watt) explained

Luminous efficacy measures how effectively a light source produces visible light. With LEDs and other light sources, luminous efficacy is the ratio of luminous flux to electrical power, known as lumens per watt (lm/w). For example, the light output (luminous flux) of a 1 Watt LED can be very bright for high efficacy or barely visible for low.

The luminous efficacy is one of the defining factors of LED performance. Top performance LEDs, with the highest luminous efficacy, have 220 lumens per watt (lm/w), such as the Nichia 757G LEDs. High performance LEDs, like those from many other manufacturers, have 150-200 lm/w. At the far end, we have the low cost, poor performance LEDs with an efficiency of less than 99 lumens per watt.

Top performance LED	High Performance LED	Good Performance LED	Poor Performance LED
220 lm/W	150-200 lm/W	100-149 lm/W	50-99 lm/W

The other light sources on the market today have luminous efficacy:

Category	Type	Overall luminous  efficacy (lm/W)
Incandescent	15, 40, 100 W tungsten incandescent (230 V)	8, 10, 13
	5, 40, 100 W tungsten incandescent (120 V)	5, 12, 17
Halogen incandescent	100, 200, 500 W tungsten halogen (230 V)	16, 17, 19
	2.6 W tungsten halogen (5.2 V)	19
	Halogen-IR (120 V)	17–24
	Tungsten quartz halogen (12–24 V)	24
	Photographic and projection lamps	35
Arc lamp	Carbon arc lamp	2–7
	Xenon arc lamp	30–50
	Mercury-xenon arc lamp	50–55
	Ultra-high-pressure (UHP) mercury-vapor arc lamp, free mounted	58–78
Fluorescent	32 W T12 tube with magnetic ballast	60
	9–32 W compact fluorescent (with ballast)	46–75
	T8 tube with electronic ballast	80–100
	PL-S 11 W U-tube, excluding ballast loss	82
	T5 tube	70–104
Gas discharge	1400 W sulfur lamp	100
	Metal halide lamp	65–115
	High-pressure sodium lamp	85–150
	Low-pressure sodium lamp	100–200

 

For an energy-efficient lighting system, we also have to consider how the light output is transferred to the desired area. The illuminance (light falling on a surface) is determined by the luminaire design and the viewing angle of the light source.

 

 

 

This brings us to the aspect of useful light or useful lumens. When we use a non-directional 360° light source, such as a light bulb to illuminate a surface (such a desk), we have a very low luminous efficacy because much of the light is emitted in other directions.

By using a light source with focus light, such an LED strip with 120° viewing angle or an LED spotlight of 60° or less, we will have higher illuminance on the desk with lower power consumption and for lower total lumen output.

A lower power light source with focused light can have more "useful lumens" that a high power bulb that is omnidirectional. Comparing useful lumens of different light fixtures is recommended when choosing the ones for a project.  

 

At Ledrise you will find many LED strips and modules with the highest useful lumens, because of the directed beam angle and also by using LEDs with the heighest luminous efficacy on the market, the Nichia 757G LEDs.