With all the talk about CFLs, incandescent bulbs and LED bulbs I was wondering... Is there a device that can be used to objectively measure the brightness of a light? Something I can use to compare bulbs in my home, auto headlights, flashlights, etc?
A light meter.
Hrm... so a heavy meter won't work? How about a kilometer?
: )
It's been close to fifty years since I've made measurements of this sort but I can recall building and using an 'integrating sphere.' The purpose is to collect and measure all of the radiation (in this case visible light) that the lamp emits. The lamp is placed within the reflecting sphere and this results in uniform brightness everywhere on the surface of the sphere. You can measure the area of the detector and the sphere and by using the ratio of these areas and the energy measured by the detector you can calculate the total energy. Many factors will influence the accuracy of the absolute measurement but for comparative measurements it's pretty straight forward.
To get a pretty good comparison I'd consider painting the inside of a large six sided square cardboard box white, placing the lamp into the box, and then measuring the brightness anywhere on the interior of the box. Be careful to not point the light meter directly at the lamp. If you place each lamp and the light meter in the same place for all measurements the comparative info should be pretty good.
if it's some odd ball bulb you can use an odometer.
s
You might compare the outputs of bulbs with similar light patterns with Robert Wilhelm Bunsen's 1844 "grease spot photometer." Put a 3x5 card with a grease spot between them and measure the distance to each bulb when the spot disappears (when it is equally-illuminated from both sides of the card.) The outputs are then proportional to the inverse square of the distances. For instance, if the card is 19" from the CF and 21" from the incandescent bulb, the CF's output is 100(19/21)^2 = 82% of the bulb's. You might screw both lamps into 2-prong sockets plugged into Kill-A-Watt meters to measure the power...
Bunsen blew himself up with explosive gases on a regular basis. He also invented the Bunsen burner, after his lab tech Desaga invented it, after Michael Faraday invented it :-)
Nick
Chances are whatever you want to measure will be a little more complex that you think. For example the light of a table lamp is one thing, but then how about a automotive head light. One needs to light up a room or maybe just your newspaper and the other needs to light up only what is in front of your car. Measuring the total light output would be OK for measuring the table lamp, but for the car you would want to measure the light getting to the road, and not any that might be lighting up the sky. Then there is the problem of color. What wavelength are you planning to measure? How about UV you can't see it, but it is light, do you measure that?
Different uses and different lamp types call for different measuring techniques and tools.
I have some fancy light meters, but one of the most useful is my digital camera.
"Calab" wrote in message news:XHP%j.177183$Cj7.174287@pd7urf2no...
If you stick with bulbs in your home, incandescents or CFLs, all you need to do is read the packaging.
As Joseph pointed out, you need different measuring techniques and tools for different types of bulbs.
The Mouser Electronics Catalog lists quite a few different bulbs and often gives the amount of light they put out. Only problem is you will have to be able to convert "End Foot Candles", "MCD", "M.S.C.P.", "Luminous Intensity", "Lumens", and probably a few more types of light measurement.
Search using key words "lamps incandescent", "lamps cfl", and "lamps led".
The Grainger catalog may have some info also.
Tony
There are meters that measure foot candles and they start around $75 and go over $200. Keep in mind, the brightness of the bulb is only one factor in proper lighting. What you generally want to measure is how much light is falling on the object you are using or working with. A bright bulb in a fixture with poor reflectivity is far worse than a less light bulb with good even light. Not to mention light color temperature.
Bright bulbs can be harsh and tiring on the eyes while a diffused light can work well for the same task. At work, I don't use any light in my office as two windows give me all the light I want most of the time. Since about early March, I've only turned the lights on maybe three times. Even then, I prefer to use incandescent over fluorescent on the desk. In the shop, we just installed fixtures with 6 T-8 lamps in them and they are very good around machines.
"Calab" wrote in news:GgS%j.305849$pM4.128336@pd7urf1no:
Barometer?
Hi, Unless you want to measure it like in the unit of Lumen, for just comparison purpose a light sensing diode and resulting current measurement possible. Stronger light produce more current.
On 5/30/2008 8:57 PM Red Green spake thus:
Sure, for bare bulbs.
Any camera which provides shutter information (shutter speed / f-stop) is a useful measurement device. Not only can a specific combination of f-stop, shutter speed, and ISO be directly translated to an objective and quantified light value, but each stop difference can be used to measure relative increase or decrease in brightness.
Smarty
Well, what I was looking for was something, with a 1" square (or whatever) sensor, that I put at a specific distance from each light source. All I want to know is how much visible light hits the sensor.
I don't need to know how well it lights a room, or the quality of the light.
Sounds like a lightmeter [light meter, luxmeter]. Measures lux- can be had for $5 at garage sales/ebay - or probably $50 or so at a camera store.
Jim
...
What's a "T-8" lamp?
Thanks!
David
Sounds like the newer, thinner fluorescent tubes.
The 6 is the number of lamps in the fixture, the 8 is the diameter of the tube (T=3DTube)
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