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A common misconception we often hear at LED Light Guides is that you can determine the brightness of a light bulb by its wattage but more watts does not necessarily mean more light. The correct way is to look at the lux or lumen of the light source for a better indication of its illuminance.
Another misconception is that lux and lumen refer to the same thing. Though they are both an aspect of brightness, they measure different things and so cannot be used interchangeably.
Read on for a quick explanation of what lux and lumen is and how to interpret their values.
How to Read Lux
Lux is the number of lumen per square meter, sometimes also referred to as the amount of illuminance from a light source. The closer to the light source, the greater the amount of lux.
If you look at the animation, you will see that the center of the square has a higher lux value than the left and right side of the square. This is because distance and direction affect this value.
This is why the same LED seems brighter in a small enclosed room than in a large open room, it is one of the advantages of LED. In a smaller space the light touches more surfaces at a closer range while a larger space has more light dispersion.
Knowing this, it is important to have a distance associated with the given lux value so you can make comparisons between different products and imagine how it impacts the task and space. Without a specific distance, this brightness indicator is incomplete and so is not informative.
What Are Lumen?
Lumen, also known as luminous flux, is the total amount of light released by a light source. Unlike with lux, this value does not change with distance.
Looking at the animation, lumen can be described as the total number of yellow specks that you see so, what is actually emitted by the light source. Since this indicator looks at what the light source releases as a whole, distance or direction are irrelevant.
Both lumen and lux can be a valuable piece of information. Where lumen gives you a global idea of the brightness, lux can provide you with more details and you may want both indicators to calculate how much you need for a specific task or space.
Let’s say the animation has a brightness of 100 luminous flux with a rating of 100 lux 1 meter away from the source. To get the same lux at a distance of 2 meters i.e. double the distance, the lumen must be doubled, as well.
Another example: your path lights cover too much area on your lawn but you still want enough brightness to see the cobble stones so what should you replace them with? Avoid glare by choosing a product with lower lux but equal amount of luminous flux.
For this same example, remember that the lighting angle should be aimed at the ground for a better focus of lux.