# How Do You Convert Watts To Lumens And Vice/versa?

Lumens and Watts are measuring different things, therefore they can not easily be converted into each other directly. The lumen is the unit given to luminous power, which measures the change in light from a surface, such as a mirror. This all comes under photometry which is the technique of measuring the brightness of light seen by the human eye.

Luminous energy is the distinguished energy of light. The human eye changes sensitivity to light with different wavelengths in the visible spectrum of the electromagnetic wave spectrum, (The human eye can only see light from the visible spectrum), and the eye is at the highest sensitivity to light when the wavelengths are 555nm (green part of the visible spectrum).

Whereas the watt is the unit for power, which is defined as one joule per second and this comes under radiometry. The Quantity that uses watt as a unit is called radiant power and it is the measure of electromagnetic radiation, such as infra-red and ultraviolet, emitted from a source.
The only main difference between lumens and watts is that luminous power accounts for human perception and the sensitivity that the eye has to different colours.

Photometric and radiometric are different from each other, however the quantities are in parallel with each other, meaning one quantity from one system will have a similar quantity from the other system. For example luminous flux and radiant flux are comparable.
Watt is the unit of power, and power isn't the measure of brightness, but it is the measurement of how much energy an object will consume.

Here is a situation, if a torch says it has an output of 4 watts and there is another torch with an output of 7 lumens, the torch with the output of 4 watts is not telling how much light energy it will produce, but just the energy it will use and this energy will be lost as heat energy, however the torch outlining that it produces 7 lumens is explaining how bright the light would be, when  produced. To convert between the two just remember 1 watt is roughly 680 lumens, because of the eyes' sensitivity to light of 550nm, but remember when looking, for example at the torches it is not about the optical power, but the brightness.
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To convert Lumen's to watts - multiply the Lumen's by 0.0015.
Watts to Lumen's - divide the watts by 0.0015
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9W Energie Savings Light is = 360Lm (lumen), so if this is true, then a 30W Energie Savings Light is = _____ Lm?

The convertion chart here and all over the internet tends to differ from site to site, and from country to country.  You would have to ask the manufaturer(s) of these light how many lumens thier Energie Savings Light is from the wattage given; they should and need to know this info.
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