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Of course, this is one of those subjects, like religion, sex, drugs, rock-and-roll and politics that I hesitate to respond to here as there are some fanatics about incandescent light bulbs in our ranks.? ?On the other hand, it's a topic near and dear to my heart as I have only a few incandescents left in my house.? ?I replaced all the PAR30 65 Watt flood lamps with CFLs at least 10 years ago, and started replacing them with LEDs starting 1/1/2014.? Out of 37 installed LEDs of all different types,? NONE have yet to fail.
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A question I have that may be of relevance to others here is how does one measure the light output of an LED?? ?This is not at all trivial, and it wouldn't surprise me in the least if the stated output, in Lumens, on the box of many of the Chinese made LED bulbs is just a lie.? ?Lumens are not easy to determine because it's the light output of the bulb, multiplied by the response curve of the human eye (the so-called photopic response, for color daylight vision).? That means you need a sensor that is closely matched to the human eye, and then you have to integrate around the bulb.? ?? Most light meters have an extended response in the infra-red, which if properly filtered can give a better response, but they are often 10-20% off from the human eye's response.? ?You can't simply apply a correction factor because the spectral output of LEDs varies a lot and it's not a simple black-body light curve like an incandescent bulb.? You have to measure the spectrum, apply a curve to it, and then integrate around the bulb.? If I were ever so lucky as to have a 7J20 plug-in for my 7854 scope, this measurement is exactly what I would be doing with it! Interestingly, I recently discovered a TI light sensor chip which has a very accurate photopic response.? It's the OPT3001.?? ?Even better, there are Chinese companies selling breakout boards (and probably knock-offs) of this chip for $5 and I have one on its way to me fro me-bay.? ?I'll just replace the chip with a free one sampled from TI.... So I am curious to play with this chip and see what kind of measurements I get from my LEDs.? ?Does anyone here have any direct experience with such light measurements of non-black body sources? ? Dan On Monday, June 25, 2018, 12:11:29 AM EDT, Ed Breya via Groups.Io <edbreya@...> wrote:
This is OT, but I just have to say I happened to stop by the Fremont Costco today, and stumbled upon some amazing deals on certain types of LED bulbs, like six-packs of PAR-xx/xxW equivalent spots for two dollars, and other stuff. They are mostly in the good warm-white 2700K/3000K range. PGE has some promotional subsidy pricing going on in some California markets, so anyone in the right areas can pick up some great deals. This is reminiscent of what they did in the CCFL era a decade or more ago. I've been an early adopter of LED illumination, and have all kinds of them collected over the years, so of course, I had to get a bunch of different ones to try out, and some more of ones that I paid five to ten times as much for only months ago. These are even cheaper than various questionable ones I've picked up at flea markets recently - and are brand new. Only certain ones (maybe slow-sellers) are priced in closeout ranges, like six-packs or two-packs for two or three bucks, depending on the particulars, but it may be worth a look. I don't know how long the deals and stock will last, but I'll be back looking for more. Usual disclaimer - no, I don't own a Costco store. Ed |
