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Dan, I think you can find the sensor pieces to make a reasonably-priced setup with good spectral matching, but the tricky part is the integration of the total bulb output, on a "hobby" budget. Commercial measurements would use an optical integrating sphere or a purpose-built structure, which can get very spendy in sizes big enough to say, stick a whole PAR LED lamp into its port. I'd recommend looking at commercial setups for ideas, and maybe you can come up with a home-made thing that will be "good enough" for your needs.

Ed

On 26 June 2018 at 00:50 "Daniel Koller via Groups.Io" <kaboomdk@...> wrote:


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.
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

On 26 June 2018 at 06:39 "Ed Breya via Groups.Io" <edbreya@...> wrote:


The integrating cube sounds good if sufficient. You can improve the uniformity and efficiency to arbitrary degrees by adding more surfaces, say starting in the corners, making it k-hedral, approaching a sphere as k goes up, but of course it quickly gets a lot more complicated and tedious. Just doing the eight corners should give a large improvement - beyond that it's diminishing returns, and lots and lots of pieces to deal with. Another option for larger sized ones that's occurred to me over the years, is to put a reasonably-accurate, suitably-sized sphere - like an over-inflated beach ball - inside a cardboard box, and fill the outer volume with polyurethane foam. After it all sets up, you can cut ports and other access to the inside, and roll the liquid coating. You could even slice it in half, and gain full access to the insides, then put the two pieces back together for use. This whole thing would be basically plastic and cardboard, so could melt or burn if you put a very hot source right in a port.

Your flat white paint should be pretty good. It may be worthwhile to see if there's any kind of super-reflective paints or coatings available, like maybe what's used on projection screens, if you want a slight improvement. The coating on my real 12" sphere looks like a flat white TiO2 DAG of some sort. I think when they make these, they pour in the DAG and roll it around to coat the insides, then dump out the excess. Also, as I recall, there's a baffle between the orthogonal ports to block any direct passage. This is more important as the ports get bigger, relative to the sphere size.

Ed

On Jun 25, 2018, at 12:11 AM, Ed Breya via Groups.Io <edbreya@... <mailto: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.

Ed,
(Sorry, careful searching for Ed’s actual email address revealed nothing.)
I know someone who is very strongly opposed to LED lamps of all kinds (also to halogen lamps). She is certain that LED lamps are very, very bad for humans.
I have not investigated the situation, but I suspect that SOME LED lamps actually put out a chopped, non-continuos light. Do you know anything about this? It seems that the normal tubular fluorescent lamps we have used for many decades do in fact emit a pulsating light, and that some few people are actually do have a negative reaction to the light.
On a related topic: just how much mercury is in the compact fluorescent lamps that are apparently not on the market any more.
In both these situations, I suspect that a heavy dose of alarmism based on some very poor science and the absence of relevant facts is in play.
Roy

I've bought some cheap led lamps (1w) for use as night lights on the landings, they actually provide useful normal levels but they do "strobe". This is only apparent when you move your hand close to them. I see blue and yellow flashes out of the corner of my eye when i blink under certain types of fluorescent lighting.
Geoff.

From: Roy Morgan <k1lky68@...>
Sent: Jul 14, 2018 3:47 PM
To: [email protected]
Subject: Re: [TekScopes] OT: LED lamp bulbs at ridiculously low prices at (some) Costco stores

Ed,
(Sorry, careful searching for Ed’s actual email address revealed nothing.)

I know someone who is very strongly opposed to LED lamps of all kinds (also to halogen lamps). She is certain that LED lamps are very, very bad for humans.

I have not investigated the situation, but I suspect that SOME LED lamps actually put out a chopped, non-continuos light. Do you know anything about this? It seems that the normal tubular fluorescent lamps we have used for many decades do in fact emit a pulsating light, and that some few people are actually do have a negative reaction to the light.

On a related topic: just how much mercury is in the compact fluorescent lamps that are apparently not on the market any more.

In both these situations, I suspect that a heavy dose of alarmism based on some very poor science and the absence of relevant facts is in play.

I have both LED and CF lamps here. I can see some strobing
from the CF but none from the LEDs. Perhaps they use a high
frequency. There are different types, for instance some cars have
LED brake and rear lamps. I can see strobing on some and not on
others.
Fluorescent lamps strobe. When I was a kid they gave me a
headache. I could see the strobing all the time. I was also aware
of the flicker on British TV. The worst was lamps at Niagra Falls
in Canada where the house current was 25Hz.

On 7/14/2018 1:04 PM, Geoffrey Thomas wrote:

I've bought some cheap led lamps (1w) for use as night lights on
the landings, they actually provide useful normal levels but they
do "strobe". This is only apparent when you move your hand close
to them. I see blue and yellow flashes out of the corner of my
eye when i blink under certain types of fluorescent lighting.

Geoff.