Saving Energy is Cool: The actual energy savings of LED lighting in an air conditioned environment

What if we told you that the energy savings associated with switching to LED lighting might be more than double what you immediately perceive them to be? You might think, "what do you mean? I can do simple math. The savings are just the difference between my existing lighting solution and the replacement. 100 (watts existing) - 25 (watts replacement) = 75 (watts saved)." You're right, for the most part, until we introduce the often important - and sometimes forgotten - variable known as air conditioning to the equation.

If you are keeping up with the exciting "green" revolution that is currently taking place in the lighting industry, you are probably already aware that switching to LED lighting technology has many benefits. The most obvious and significant benefit is the energy savings that you can achieve by making the LED switch.  But how significant is it? Well, that answer may surprise you... Let's take a look at an example or two.

Before we get started, let's cover a couple of assumptions that we'll make in order to simplify things:

1) Relative to conventional lighting technologies, LEDs are very good at converting electrical energy to light energy.  We are going to assume that the LED light source is 100% efficient at converting electrical energy to light energy.

2)  The average air conditioning system is only about 70% efficient.

 

Now on to our examples:

Let's take the most historically dominant consumer bulb on earth; the 60 watt incandescent bulb.

Let's say that you are replacing a 60 watt incandescent bulb in an outdoor post light with a new "light equivalent" 9 Watt LED bulb (when we refer to "light equivalency" of an LED light vs. the conventional alternative, we mean an LED light that produces the same amount of useful light energy as the existing lighting solution). In this case, the 9 Watt LED bulb yields an 85% reduction in energy usage over the 60 watt incandescent bulb which translates to an 85% monetary savings in energy usage for that application. The math is straight forward because 9 is 85% less than 60.

Now, let's look at a different application.  You want to replace a 60 watt incandescent bulb that is installed in a floor lamp in your living room. Let's also say that you live somewhere where it is warm enough outside that your air conditioner is running.  In this situation, the actual energy savings becomes much more significant and the math to calculate the savings gets a bit more involved. In order to correctly calculate the financial benefits of switching to a "light equivalent" 9 Watt LED bulb in an air conditioned environment, you must account for the AC-factor.

What's the AC-factor? Well, it turns out that almost all of that power difference between the new LED technology and the conventional lighting is actually excess heat energy, which gets dissipated into the environment (an air conditioned room, in this case) as a result of the fact that old lighting technologies are less efficient at converting electrical energy into light energy.

OK, so what's the big deal?

Well, the fact of the matter is that accounting for the excess heat of the conventional technology in an indoor air conditioned environment results in an overall LED energy savings that will be more than two-times your calculated savings of our first outdoor example.  Let me explain.  Because that simple 60 watt incandescent bulb is actually adding 51 watts, (60 watts minus 9 watts), of additional heat into the space that your air conditioner is already trying to cool, that requires the air conditioner to use extra energy to get rid of that added heat.  In fact, because the average air conditioning system is only about 70% efficient, that extra energy used by the air conditioner is even more that the energy added by the bulb. In this case, the extra energy is an additional 66.3 watts to offset that 51 watts of heat added by the 60 watt incandescent bulb.

I realize this might be a little confusing but if you add up all of the energy savings of switching to a "light equivalent" 9 Watt LED bulb, the savings looks more like 117.3 watts of savings. This would actually make the savings more like 93%.  This is because when adding the extra air conditioning burden of operating a 60 Watt incandescent bulb,  the power company would need to supply 134.1 Watts of energy vs 9 watts for the LED bulb. Now imagine the energy savings that would result from switching to LEDs in large indoor commercial spaces!

Check out some of BrightWay's great products for interior LED Lighting by clicking HERE.

 

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For those of you who are really interested in the math of these examples, you may take issue with my analysis. OK, yes, I have simplified things a bit.  If you were to really scrutinize the analysis, it would be concluded that the actual savings is more like 89% rather than 93%. Here's why. I stand by the statement that "relative to conventional lighting technologies, LEDs are very good at converting electrical energy to light energy". However, the truth is that although they are good, they are not 100% efficient. Semiconductor companies are investing heavily to continue improving the efficiency of LED's.  In actuality, a good quality 9 watt LED bulb will actually produce about 5 watts of heat energy. Mathmatically, I assumed that 51 watts of heat is produced from the 60 watt incandescent bulb.  Incandescent bulbs are only 5% efficient, thus the actual heat produced is more like 57 watts.

All in all, the simplified model yields pretty good approximations for the energy savings. The model is meant to give a fairly close estimate while keeping the math simple and straight forward. For those of you that you who like to really crunch numbers, send us an email at customerservice@brightwaysupply.com and we can provide you with a spreadsheet that allows you to more accurately control the parameters of the calculation.

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