420 Lumens to Watts Conversion

420 Lumens to watts is typically 4.7 watts using LED, but is dependent on the efficiency of the light source.

The outdated metric of using wattage to judge brightness is over, as LED lights use less power to produce the same amount of lumens and can differ according to design. So a new comparison needs to be made.

420 Lumens to Watts By Light Type

To known what is 420 lumens in watts, use each light source’s watts to lumens efficacy, typically:

• 36 Watts with Tungsten Incandescent
• 4.7 Watts with LED
• 5.6 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:

Candelabra LED Bulb

A 420 lumens B10 / B11 LED bulb will use 3.56 Watts @ 118 lm/W

GU10 LED Par16 Spot

420 lm LED Spot GU10 2700K PAR16 uses 4.47 Watts @ 94 lm/W

LED Light Bulb A19

A 420 lumens A19 2700K LED bulb will use 4 Watts @ 104 lm/W

LED Recessed Ceiling Light

An 420 lumen recessed ceiling light requires 5.45 Watts @ 77 lm/W

Fire Rated LED Downlight

A recessed downlight with an 420 lumen output requires 4.2W of circuit power @ 100 lm/W

LED Strip

A 4.8 W/m 70 LED 3000K strip will use 4.94 Watts to create 420 lm @ 85 lm/W

Understanding Lumens & Watts

As lumens measure the amount of light and watts the amount of power used to create that light, now efficiency is considerably better with LED, the wattage has become an outdated benchmark for brightness as a small amount of power will now create a lot of lumens.

Lm/W Efficacy

To convert 420 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: 50-250+ 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 5.25 watts to produce 420 lumens.

420 lumens / 80 lumens per watt = 5.25 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.