What is LED luminous efficacy (lumens per watt)?

What is LED luminous efficacy (lumens per watt)?

Luminous efficacy measures how effective a light source produces visible light. It is the ratio of luminous flux to electric power, the value of 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 performance LEDs with an efficiency of less than 99 lumens per watt.

Top performance LED High Performance LED Good Performance LED Low 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 the following 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 a high energy efficacy lighting installation, we also have to consider how the light output is transmitted to the required area. The is called illuminance (light falling on a surface) and is based on the fixture design and light source viewing angle. 



The image below shows that the same light source can have a different illuminance when placed in different fixtures. For the same power consumption we can have too less, just right, even and optimum illumination or too bright illumination in some spots.


This introduces the concept of useful light output, or useful lumens. If we use a non-directional 360° light emitting lamp, such as an incandescent bulb, to light the surface or our desk, we will have a very low luminous efficacy because much of the light is emitted in other directions. However, by using a light source such an LED strip is a 120° view angle or a LED spot with 90° or less, we can achieve the same illuminance on the desk with lower power consumption and less total lumen output, thus the term "useful lumens".


At Lumistrips 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 highest luminous efficacy on the market, the Nichia 757G LEDs.

LumiFlex with Nichia 757G 220 lm/w LEDs