- “How bright of a bulb do you need in that light fixture?”
- “60 watts.”
- “Ok, got it.”
We’ve all been part of a similar conversation before. But there’s a problem with it: It makes no sense at all.
It has become common and ingrained in our minds to think of how bright a light bulb or light fixture is based on its wattage. A 60-watt bulb meant you got 60 watts of light. That’s how it’s been for decades. But watts are not a measure of light output. Rather, they are a measure of how much energy a light source is consuming.
What we’re after here is brightness; the amount of light emitted by a light source. How bright is that light bulb or fixture? How much light is it giving off? The unit of measurement to determine how much light a lamp or luminaire emits is called lumens
The lumen output is what determines brightness and is the term and measurement we should all start to get very familiar with.
Older incandescent bulbs converted their used energy into visible light at a predictable rate (albeit terrible), so we were very familiar with it. But new LED technology is changing all that; requiring far less energy to give off the same amount of light. And with LED technology constantly evolving and becoming more efficient, it is becoming more and more important that we become comfortable with lumens.
Comparing the Different Technologies
So how do these all stack up? How many lumens did a traditional incandescent 60-watt light bulb give off? What’s the modern LED equivalent?
Time for charts!
This is just a general guide only, and limited to general purpose, household omnidirectional bulbs and their common brightness levels. The efficiency at which an LED converts the energy it is consuming into visible light (its efficacy) is improving all the time, so its wattage usage will continue to go down and down for the same amount of light output.
It is worth noting that as you scale up and start getting into larger bulbs and light fixtures with more intense light output, additional factors come into play when comparing different lighting technologies and you need to look beyond simply the lumen output.
is one such factor. This is increasing common in commercial and industrial applications. For example, suppose you have a parking lot light that uses a 250-watt metal halide HID lamp. That 250-watt bulb outputs roughly 14,000 lumens (on average) in all directions. But you don’t need the light in all directions; you only need the light down on the surface of the ground. With traditional lighting, a good percentage of light is lost before it hits the ground, often escaping into the fixture housing or diffusing as it bounces around the housing’s reflectors. The intensely powerful and energy-consuming HID lamp is needed in this case so that enough of its light makes it down to the ground.
Suppose you want to upgrade that same parking lot light fixture to LED. Does this mean you’d need to find an LED area light that outputs the same 14,000 lumens? No, not necessarily. Because LEDs are inherently directional, all of their light is pointed towards the target surface (in this case, the ground). Depending on the situation, you might be able to use an LED fixture that outputs only 7,000 or 10,000 lumens.
There are many other factors that affect the light output of a fixture or bulb, called Light Loss Factors. These include ballast factor, ambient temperature, voltage, optics, burnouts, lumen depreciation, and more.
While it can get confusing at first to try and factor them all in to create a true apples-to-apples comparison of high-output fixtures and lamps across different lighting technologies, the bottom line is that often you will be able to use an LED that, on paper, has less lumen output than the traditional light source
. So not only will you save energy by simply switching to LEDs, you will likely be able to step down to a lower output fixture because of the increased optical efficiencies of LED fixtures, while maintaining the same foot candle levels at the target surface.
Naturally, this can vary greatly per project, depending on various conditions. But as an overall guide, here are some common equivalents. Note the difference in lumen outputs.