I wasn't sure the price was correct. Normally when I walk through Lowes, I check the price of LED bulbs. It seems they have always been between 11 and 15 dollars for the kind that would screw into a standard light fixture. This one said "$2.48". That can't be correct—but it was. At a price of under 3 dollars, this light bulb was a must buy. So I purchased it. Now for the testing.
The box says it is like a 60 Watt incandescent bulb but only uses 9.5 Watts. Let's check if this is true. Oh, and for fun I will look at some other bulbs: a compact fluorescent, and three incandescent bulbs (60 W, 100 W, 200 W). Yes, I found a 200 Watt bulb—I'm pretty sure you can't buy these anymore.
I just need to plug each bulb into the Watts Up Pro and then turn it on. Actually, I also used Logger Pro (from Vernier) to look at the power as a function of time. I wanted to see if there was a significant power change as the bulb warmed up—there wasn't. Here are the powers for each bulb.
There are actually two more bulbs in there. I had a 100 Watt incandescent bulb with clear glass (instead of the frosted glass) and then there were two compact fluorescent bulbs with different power ratings (13 and 15 Watts). Maybe this data isn't all too surprising. I did find that the LED bulb was listed at 9.5 Watts but measured at 10.43 Watts. Really, all the bulbs were off of their rating. The 200 Watt bulb only used 191.6 Watts but both 100 Watt bulbs were running at 110 Watts. Oh well, it's not a big deal.
I know what you are thinking—sure the LED uses less power, but they aren't bright enough. Nothing is bright enough for me except for the 200 Watt incandescent bulb or maybe the Sun. So, just how bright is the LED. I will first tell you that it looks fine (just to the naked eye). But how about some measurements? For this test, I am going to use the Vernier light sensor. Now, it's possible (and entirely likely) that the light intensity is different at different angles from the bulb. To make sure the bulb distributes light uniformly, I will put the bulb on a rotation sensor and rotate the bulb while collecting intensity data with the sensor that is 69 cm away. Here is the data for the LED, 60 and 200 Watt incandescent bulbs and the 13 W compact fluorescent bulb.
You should be able to notice two things. First, the light is fairly uniform as the bulb is rotated. I'm not sure why there is that dip in the 200 Watt bulb, but I am going to guess that maybe my hand got in the way or something. Second, the all the other bulbs have about the same brightness.
What if I mount the bulb horizontally and rotate it? Like this (except the data was collected in a room that was dark except for the light bulb):
There is one difference between the LED and the other bulbs. All the other bulbs increase (at least a little bit) in intensity as the bulb is rotated to its side. Why? When you look at the bulb from the top (zero radians in the graph), all the bulbs pretty much look circular. However, take a look at the LED and the 200 Watt bulb as viewed from the side. For the LED, much of the side profile is not illuminating at all. Really, it's just like part of a circle when viewed from the side such that the intensity at some distance away would be less than viewed straight on. Now take the 200 Watt bulb. Notice how long it is? All of that stuff on the side would be glowing which increases the intensity of light when viewed that way. Of course, once you start getting to viewing angles from the bottom of the bulb the intensity decreases because the bulb holder starts blocking some of the light. But is the LED as bright as other bulbs? Well, nothing is as bright as the ridiculous 200 Watt bulb. But the LED seems very comparable to the other lights. It does decrease in light intensity when viewing from the side, but it still seems bright. But what about the total light produced for each bulb? I'll look at that in a future blog post.
You can think of a lightbulb in terms of energy. You put some electrical energy into it and you get light energy out (not the correct technical terms). However, there is a problem—you also get heat energy out of the bulb. The more heat you get, the less light you get. The most efficient bulbs will have less heat output and won't be as hot. Let's look at the temperature of these bulbs by plotting temperature (at the hottest point) by power.
This doesn't exactly tell you the efficiency of the bulbs. The 200 Watt bulb gets super hot, but it also produces more light than the other ones. But still, it's not very efficient.
The hottest part is the base of the bulb where I suspect there is an AC to DC converter which is the primary source of heat for this bulb. For the incandescent bulbs, the hottest part is the top of the bulb.
"But I would never use an LED bulb. They just don't create the same color light as an incandescent." Yes, that would be another complaint. But is it true?
There is a quick and easy way to look at the colors of light produced by each bulb. If I pass the light from the bulb through a diffraction grating, different colors of light will be bent different amounts. This will allow us to see which colors a bulb produces.
I should do a more complete investigation (with better equipment), but you can still see the difference. The LED has about 5 different discrete colors where the other bulbs have continuous color distributions. Actually, I am sort of surprised that the compact fluorescent gives fairly continuous colors—I can't even tell which spectrum is for that bulb. However, the LED still produces colors in the same range. When you look at it, it mostly appears white and that's a good thing.
Is there anything else that is important about the LED bulb? Yes, there is one other major factor—lifespan. Do incandescent bulbs last forever? No. There are two problems with the incandescent bulb. First, if you shake them too hard, the fragile filament inside can come loose. Without an attached filament, you have no current and no light. Second, air can leak into the bulb over time. If enough air gets into the bulb, the filament will burn instead of just glowing. This causes the filament to melt and then you again have no light.
Fluorescent bulbs also have a limited lifespan. In order to excite the gas inside the tube, you need a high voltage created from an electronic ballast. If this ballast gets too warm, it stops functioning. Also there can be a problem with the gas in the tube—you can't let it leak out.
The LED is just a solid state device—no gas needed. Shaking it won't really do too much to it either. Of course it still has some electronic components (probably and AC to DC converter). This won't last forever, but still the box for the bulb I tested says that it has a lifespan of 15,000 hours. That's 13.7 years if you use the bulb for 3 hours a day. I guess I will have to write a follow up blog post in 14 years.
Since I didn't cover everything, here is some homework. I plan to answer some of these in a future blog post, but here they are just in case.
12v Led Swimming Pool Light
Flood Light, High Bay Light, Street Light, LED Strip Light, Tube Light - Szdera,https://www.szdera.com/