Do all bulbs of the same wattage emit the same amount of light?
No, they consume the same amount of energy.
Check for Lumens, that is the rating for amount of light put out
In fact the difference between light output for a given wattage (or conversely, the wattage required for a given lumen output) is absolutely huge between incandescents and more efficient technologies – CFLs consume about one-fifth the power of incandescents for a given light output, and LEDs even less. Incandescents turn most of the input energy into heat – the emission of light is essentially a minor side effect!
I assume you are talking about incandescent bulbs here. Generally tungsten filament light bulbs are pretty consistent from bulb to bulb over different manufactures. You can move the efficiency around some by running the filament hotter or colder. Generally hotter is more efficient as more energy is released in the visible spectrum instead of infrared, but that decreases the life of the bulb.
LEDs and compact fluorescent bulbs are very different from incandescent and there is a lot of variation from manufacturer to manufacturer and bulb type.
And neither do sound systems. Wattage is only telling you how much power it draws. not how much light or sound it outputs. It always confused me why anyone ever started using wattage as a measure of performance. People who buy lights and sound systems based upon wattage often end up buying expensive inefficient heaters.
Umm…no.
Wattage in sound systems is a rating of how many watts (usually per channel) that the amp can deliver to the speakers at a specified distortion level. When the input is not cranked to 11, the amp will not consume nearly it’s rated wattage.
Right, but a 60 watt incandescent is much the same as any other 60 watt incandescent- there may be some slight variation, but for all intents and purposes they’re fungible. They put out somewhere between 800-900 lumens. (the one I looked at on Home Depot’s site put out 830 lumens @ 2700 k)
Same goes for CFLs of the same equivalent wattage (i.e. 60w equivalent)- they all roughly put out the same amount of light as the aforementioned 60w incandescents, but they do it on something like 14 actual watts.
60w equivalent LED bulbs are more efficient yet, putting out roughly the same lumens for about 9 actual watts consumed.
So yeah, all 60w equivalent bulbs put out between 800-900 lumens, but the actual wattage used varies significantly.
In about ten seconds of Googling, I was able to find a long-life 60 W bulb at only 780 lumens. That one was billed as “double the life”; I’m sure a more diligent search could find more extreme examples.
And the wattage of a bulb absolutely is relevant, as it will determine what wiring you’ll need for the circuit, and how much heat your fixture will need to be able to deal with. It’s just not the only relevant stat.
As an aside, it’s not very relevant now that incandescent bulbs are so rare, but long-life bulbs are almost never a good idea, unless the bulb is in some location that makes it extremely inconvenient to change it. The replacement cost of a bulb is far less than the cost of the energy it uses over its lifespan.
As said watts can vary all over the place depending on the technology. There is this term called lumens that perhaps will become common someday, till then you can use the ‘Watt Equivalent’ which relates the light output to the wattage of a standard IC bulb.
Bulbs sold in the US now have to indicate brightness in lumens and power used in watts on the packaging. It has to be displayed in a standard format much like nutrition information of packaged foods. I think that this has been the case for a few years.
It may be required to have lumens, but my statement was more that people don’t use that measure, and many still look for watt equivalent.
The current trend is to ban (simple, traditional) incandescent and allow the halogen incandescent aka “halogen”. The difference is that the halogen bulb has the filament surrounded by halogen gas, and the halogen gas is deliberately raised to a high temperature.
To the consumer this means that the bulb looks , at the outside, like an incandescent, but the halogen feature makes it brighter, for the same power.
Simple incandescent turns about 2% of the consumed power into light.
Halogens do the job a bit better and turn about 3.5% into light.
So basically a 60 Watt halogen is as bright as the old 100 W incandescent…
Some packaging may not make it clear that the halogen bulb is that much brighter than regular.
At least in my area, they’ve recently begin marking them as say… “60w Equivalent”, so people do have some idea how they compare.
Interestingly enough, halogen bulbs aren’t that much brighter. I did some quick calculations to figure out the lumens per watt of the 4 main types of bulbs and here’s what I found:
Incandescent: 13 lumens / watt
Halogen: 15 lumens / watt
CFL: 65 lumens / watt
LED: 84 lumens / watt
So the halogens are brighter for the same power, but not even in the same league as CFL or LED bulbs. Basically a 60w equivalent halogen would be in the 45-50 watt of consumed power range. Great back in 2000, but not so great nowadays.
Depends on what you are looking for, there is light quality to consider, CRI is just one of these measures but not perfect. So yes you can get ‘light’ for 9 watts, or you can get LIGHT for 60 Watts (or 43 for Halogen).
Admittedly LEDS are a vast improvement over CF, but not quite there yet, but close.
What happens to the rest of the energy? Where can it go in a sealed bulb?
It gets out as heat.
The wattage of a light source is no longer useful as a guide to how much light you will get from it. In Europe at least, the Lumen is taking over as the standard method of comparison.
We should also learn about colour temperature - correlated color temperature (CCT) which uses Kelvin temperature measurement scale to describe the relative color appearance of a white light source. This ‘K’ number indicates the brightness of the light - whether it appears warm or cool. A typical 8000K LED would be bright white and a 3000k lamp would look more like the current CEF or incandescent lamps.
To convert Watts to Lumens go here
For a CCT chart, go here
As an aside - many people think of LEDs as tiny little lamps. They can now mimic most types of light fitting, including fluorescent tubes.
In general, whenever the question is “where does the energy go?”, the answer is almost always “heat”.
It’s a good question.
This leads directly to the issue of why LED lamps have strange heat-spreading devices on them, something that regular lamps don’t. A standard incandescent lamp operates at a much higher temperature than an LED - the materials it is made of (glass and metal) can withstand many hundreds of degrees, and so most of it’s waste heat gets radiated away. LEDs need to operate at much lower temperatures (well under 100C, for long life). Because of these, most of their waste heat needs to be convected away - the operating temperature is too low for radiation to play a significant role.
Most of the energy output from an incandescent bulb is in the infrared range, which does not help you see any better, but does keep you warmer. However, enough of it is in the visible range to serve as a “light” bulb.