400 Lumens to Watts Conversion

If you need to know how bright is 400 lumens by conventional wattage, it’s 34 watts.

That metric is however outdated as the era of incandescent lighting is over. Less power is required with LED lighting to produce the same amount of lumens, so a new comparison needs to be made.

400 Lumens to Watts By Light Type

400 lumens of light on average is:

• 34 Watts with Tungsten Incandescent
• 4.49 Watts with LED
• 5.33 Watts with CFL

Not all LEDs require the same amount of power to create the same light output. Here are some example products and their corresponding wattages:

LED Light Bulb A19

A 400 lumens A19 2700K LED bulb will use 3.85 Watts @ 104 lm/W

Candelabra LED Bulb

A 400 lumens B10 / B11 LED bulb will use 3.39 Watts @ 118 lm/W

GU10 LED Par16 Spot

400 lm Philips Master Value LED Spot GU10 4000K PAR16 uses 5.19 Watts @ 77 lm/W

LED Recessed Ceiling Light

An 400 lumen recessed ceiling light requires 5.45 Watts @ 77 lm/W

Fire Rated LED Can Light

A recessed ceiling can light with an 400 lumen output requires 5.56W of circuit power @ 72 lm/W

LED Strip

A 4.8 W/m 70 LED 3000K strip will use 4.71 Watts to create 400 lm @ 85 lm/W

Solar Security Floodlight

To achieve 400 lumens output an IP66 solar floodlight will use a 4W 6V panel to charge and power it.

Understanding Lumens vs Watts

As lumens measure the amount of light and watts the amount of power used to create that light, the only accurate way to calculate the power consumption in Watts, is to know how efficient the light source is.

Lm/W Efficacy

To convert 400 lumens to watts, we first need to know the efficacy of the light source.

Efficacy is a measure of how well a light source produces visible light. It is measured in lumens per watt (lm/W) or light output per watt.

A higher efficacy means more light for the same amount of power, with different light types and even different models within a light type varying quite a bit.

For reference, here are some average lm/W efficacies for various light types:

• Compact Fluorescent Lights (CFLs): 60-90 lm/W
• Tungsten Incandescent Lights: 12 lm/W
• LED Lights: 50 lm to 250 lm/W (varies widely by LED)

Lumens to Watts Calculation

So now a more accurate lumens to watts calculation is required to find out how much power your LED light will consume.

The power in watts (W) is equal to the luminous flux in lumens (lm), divided by the luminous efficacy in lumens per watt (lm/W):

Watts = Lumens / Efficiency

For example, an LED with an efficiency of 80 lumens per watt would require 5 watts to produce 400 lumens.

400 lumens / 80 lumens per watt = 5 watts

Andrew Orange, the owner of Orange Lighting qualified and worked as an interior designer in 1993 before specialising in lighting working on high profile projects based in London. Since starting Orange Lighting Ltd in 2003 he has been sharing his knowledge and unique teaching style mostly to his designer clients, offering practical real life advice born from running a busy consultancy and lighting supply business. Launching in 2020, his blog has evolved into Quick & Easy Lighting, curating some 25 years design experience into making the lighting choice and design process achievable and easy to understand for all.