Integrating sphere #4 (the fast and cheap one)

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djozz
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Ah, I see. My spheres are for measuring, yours is to make what they call a lambertian light source Smile Then my story does not apply to your situation. And yes, you can paint any sphere flat white on the inside, styrofoam spheres are simply the cheapest and most available spheres, that is why I use them.

I found that any white coating of the sphere warms up the light of the source, typically by 500K to 1000K (some blue is lost) It will depend on the coating. If that is not a problem, any coating will do.

I was just discussing spheres with member Moderator007 the other day and he found that molds for “Atlas stones” may be a good material for an integrating sphere. Unfortunately that is a very US product so on top of them being more pricy than styrofoam, shipping will be high to Denmark.

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Thanks Djozz! I will look for Lambertian light to see what’s up =)

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So I’m learning that my DIY sphere (shown back at post# 64) is apparently wildly inaccurate at higher lumen levels (+/- 400 lumens and above) and it doesn’t seem to matter what size flashlight is in the hole (so I don’t believe it’s related to light reflecting off the bezel/glass lens). I’m wondering if it’s related to light loss through the sphere wall, where lower lumen levels wouldn’t see much light loss, but higher outputs would. Thoughts? A few years back I posted these lux readings where I experimented with covering my sphere with a thick black towel, but I only used my Convoy S2 EDC (high mode on that light is only +/- 500 lumens). FYI – my sphere calibration/multiplier is derived from measuring three different Fenix HL55 headlamps and averaging the results. (Note that I’ve never had a light that shows steady well regulated output at levels about +/- 400 lumens, so my multiplier(s) are computed with “low” and “medium” output levels). I’m not trying to nail down exact lumen #‘s from lights (I understand I’ll be off +/-10% of “true”), but looking to have a multiplier that works consistenly from 1 lumen to +/- 2,000 lumens.

Here are 3 sphere results that have led me to question my calulated lumens at higher levels (all lights measured using fully charged hi-drain cells):

Sofirn SP40 (XP-L 4,000k):
Low = 6.6 Lumens
Med = 62.8 Lumens
High = 306 Lumens
Turbo = 798 Lumens

Sofirn SD05 (on a brand new Molicel P42A 21700)
Low = 277 Lumens
Med = 792 Lumens
High = 2,223 Lumens

Astrolux HL01 (XP-L 4,000k)
Stepped Ramp Levels:
Step 1 – 13.0 lumens
Step 2 – 43.9 lumens
Step 3 – 124 lumens
Step 4 – 162 lumens
Step 5 – 253 lumens
Step 6 – 404 lumens
Step 7 – 690 lumens
Turbo – 992 lumens

I immediately questioned my results on all three lights above 300 lumens. In this post, user YogibearAl gave me his calculations for the SP40 (which sound good to me) and so I used those to re-calculate new multipliers for each mode. My previous multiplier was 0.4275, and now trying to calibrate to Yogi’s #‘s I am getting varying multipliers, with the #‘s for the high outputs being significantly higher (my expectation – that my sphere is “good” at low outputs, but gets exponentially worse at higher levels). Multiplier’s I get:

SP40
Low – 0.4516
Med – 0.4422
High – 0.5000
Turbo – 0.5158

If I then run with the multiplier of 0.5000 from high mode, run that back against my SP40 measurements and also on my SD05 & Astrolux HL01 (XP-L 4000k) measurements, I get:

SP40
Low – 7.8 lumens
Med – 73.5 lumens
High – 358 lumens
Turbo – 934 lumens

SD05
Low – 324 lumens
Med- 926 lumens
High- 2600 lumens

Astrolux HL01
Stepped Ramp Levels:
Step 1 – 15.2 lumens
Step 2 – 51.3 lumens
Step 3 – 145 lumens
Step 4 – 190 lumens
Step 5 – 296 lumens
Step 6 – 472 lumens
Step 7 – 807 lumens
Turbo – 1160 lumens

So now my higher numbers seem much more in line with expectations, but I suspect I’m showing lumen #‘s that are too high for the lower levels. So what am I supposed to do, use different multipliers for different lumen output ranges??? And how would I know what I am doing is reasonably accurate?? Is anyone else using these round styrofoam spheres seeing the same issue I am? Do I need to paint the outside of my sphere to stop light loss? Should I test lux readings with the towel again with higher output lights? Is a towel really causing light not to get “lost”.

Thanks,
-Garry

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I will have a closer look at your numbers above, but there are a few things that I am fairly sure of:

*luxmeters are as far as I know very lineair, so if you start with a reading at a low setting, then 10 times as much light should get you a 10 times as high reading, and 1000 times as much light should get you a 1000 times as high reading.
*same goes for light loss through the sphere wall (light loss is no problem at all as long it does does get over a certain percentage), the same percentage is lost from very low to very high light levels.
*and thus: for the same spectrum (tint+CRI) the same multiplier should be used for all output levels.

So either your numbers are “more right” than YogibearAl’s, or something is going on with your measurements that I do not understand yet.

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Thanks for checking into things djozz! The statements you’ve made above I’ve read elsewhere, but puzzle me since they don’t seem to be holding true for my sphere (i.e. that one single multiplier computed from lower lumen levels should work for higher outputs). I don’t trust my higher lumen numbers at all. I’m sure that the SD05 on medium should be at least 900 lumens, if not more. I’ve not scoured BLF looking for user’s results who have the same lights measured in light measuring devices which seem verified as trustworthy – I only posted asking in the SP40 thread and Yogi responded. It also seems it would be difficult to try to “calibrate” to a light with a higher output as most high outputs are not steady (as I’m sure you know). The SD05 is one that is fairly steady on medium, although another user would probably have to test it with an identical battery for me to compare to. I have one bike light (highly modded though) which seems very stable at higher output levels, but I would need someone else to measure my own light as no other light exists modded like mine.

Here is a recent video showing measurement & analysis on my SD05 (on a different battery) for what it is worth.

Thanks!
-Garry

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I’m also wondering if I should be adding diffusion material (like trying to put a sheet of DC Fix across the bottom of my sphere opening – though I could see it peeling away and being a constant problem). Any change with my sphere means trying to get a hold of those Fenix headlamps I originally calibrated with which is now much more difficult to do!

Also, what about the fact that my luxmeter is simply pressed into the side of the foam without the foam actually being fully cut out? Should light in the sphere reach the luxmeter sensor itself withut going through foam?

Thanks,
-Garry

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Okay, I’m planning to build sphere #2. I’ve picked up another (2) hollow 12” styrofoam balls identical to my first sphere. I did catch that I believe my styrofoam balls seem to have thinner walls than djozz’s (could this be part of my problem? – Perhaps why so much light seems to escape through?). Mine looks like this one|540:540.

Anyway, with this one I am looking to still have a +/- 90mm entrance hole, but this time fit a piece of glass with DC Fix attached to the underside of it into the entrance hole. Sourcing a 4” round piece of glass is more difficult than I thought it would be! I have looked into obtaining diffusion lenses used in LED recessed lighting, but that seem difficult and expensive if buying the entire light for the lens. It also seems that the 6” recessed lights frequently have a lens that is only about 3 1/2”. I did manage to pickup a clearanced recessed light which I was able to remove a 3 1/2” × 3 1/2” square diffusion lens. It is plastic, does a wonderful job of diffusing a flashlight beam into a smooth wide wall of light without any throw, but seems it would be difficult to mount and would be too small to still have a 90mm round hole. I think on this sphere I will paint the inside with white acrylic matte finish paint (after sanding the foam). I then think I will cover the outside of the sphere with brown paper and glue (got the idea reading this technical article on a cheap I.S.).

I’m unsure if I should change anything with the luxmeter. I might just start with the same setup I have now – dig out some of the wall (perhaps a bit more this time) and mount the luxmeter against it. I was also thinking to fully remove the styrofoam creating an opening for the luxmeter, but first attach a PVC pipe 90º elbow so that the light can’t directly reach the luxmeter sensor. Also thinking to maybe add DC Fix at this opening as well. I’m considering adding a baffle in front of the lux meter opening too, but not sure if it’s needed or not. Maybe I’m already changing too many things to see what the problem on the first sphere actually was!

So any thoughts on what I’m planning? Does any of this seem wrong? Djozz?

Thanks,
-Garry

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djozz
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I like those styrofoam balls from your link, they are nicer than mine because they are completely spherical on the inside while the balls that I buy have some holes that I have to fill up. The wall thickness looks fine to me, similar to the 2cm of my spheres.

About light passing through the wall, don’t worry about that, reflectivity will not be 100%, almost 90% if you are lucky, that 10% will go somewhere and part of it makes it through the wall and can be seen. What is important is the 90% that is reflected, not what happens to the 10% that is lost with each reflection.

Coating the ball with brown paper in the article is to prevent ambient light to enter the sphere and influence the reading. My integrating sphere is built into a plywood box that works as such (and is convenient because you can put stuff on top of the flat top).

You can try all sorts of diffusion but mind that every diffusion step selectively removes some blue light from your lightsource, so lightsources with a high blue peak in the spectrum will more and more undermeasure compared to souces with little blue. (but I don’t know by how much). So keep the diffusing steps limited.

In case you make a hole for the sensor: a baffle before the sensor is not good, the sensor should “see” as much of the sphere as possible, only the hole where the light comes in must not be in sight for the sensor, it must be blocked by a baffle, about halfway the entrance hole and sensor.

Btw, I still do not see what is wrong with your first sphere, when you posted pictures it looked pretty ok to me.

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Umm . . . I started working on my new sphere and ran into an issue. While sanding the inside with 400grit sandpaper, the sandpaper would pull small pieces of styrofoam out causing what look like gouges. Is this going to be a problem for me? I’ve already applied two coats of matte white acrylic paint to the inside, plan to apply two more coats, but the paint isn’t really filling in the gouges.

Some pics:

And Painted (one coat in this pic):

-Garry

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djozz
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Should be no problem at all for integration of the light.

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Ok, good. I’m still trying to decide how to proceed with the rest of the construction – paint outside black? (Read in a forum post not to because black absorbs light. Also, will it matter since I am painting the inside with paint? I’m not trying to keep ambient light out, I’m trying to keep the source light in.) Cut mount hole for lux meter sensor completely through to inside of sphere? Set lux meter sensor back off sphere surface with PVC? Add neutral density filter in front of lux meter sensor? Add baffle(s)?

One thing I will definitely do is add diffusion film/lens at the light entrance hole. I can’t think of a good solid way to mount that to the inside edge of the foam, so I’m planning to cut slits into the sides of the entrance hole and insert the glass/lens into those slits. I will have to do this where the two foam halves meet so I can assemble the halves together with the glass/lens in the slits. I can only find a 4 inch glass at 3/32 inch thickness and even that is a little costly. (It happens to ship from just 30 miles away from me, so I’m tempted to try to pick it up when I’m nearby.)

I know what will happen – I will go through all of this and still have a sphere that gives erroneous readings at certain levels.

I wish more foam sphere builders would post up their findings on what works, what doesn’t, etc. I did find a post over at CPF where the person used their sphere for awhile and discovered it to be inaccurate above +/- 400 lumens just like me.

-Garry

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I wonder how you are sure that the reading of your sphere at higher lumens is much off? Nothing what I know of the construction of spheres or the working of luxmeters, supports that. I’m not saying that is not possible (I do not know everything) but please also consider that your readings are correct and your outside information about the lights you are measuring is wrong or incomplete (like they fail to mention that it was measured at 0 seconds instead or 30 seconds, things like that).

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Sorry I haven’t read this whole thread.

I know for higher output lights you really want a bigger sphere.

Have people tried mixing barium sulfate into a paint like mixture to coat the insides?

Texas Ace Lumen Tube and JoshK Sphere calibrated with Maukka lights

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djozz
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Directly for the measurement itself, the size of the sphere is unimportant, a sphere integrates the light and does that regardless of the amount of light.

But there are three other reasons for a bigger sphere at higher output:

1)A bigger sphere is needed because high output lights usually have bigger heads and thus the entrance hole must be bigger and to keep the surface percentage of the hole within the required maximum the sphere needs to be bigger.

2)the amount of heat may melt your styrofoam, going bigger spreads the heat over more material.

3)your measurement may get your luxmeter out of range, a bigger sphere increases the range. But a ND filter before the sensor does that too.

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I have done BaSO4 coatings on test spheres, tried mixed with latex paint, and mixed with PVD. I did all sorts of checks but I found it difficult to find clear advantages over bare sanded styrofoam.

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djozz wrote:
Directly for the measurement itself, the size of the sphere is unimportant, a sphere integrates the light and does that regardless of the amount of light.

But there are three other reasons for a bigger sphere at higher output:

1)A bigger sphere is needed because high output lights usually have bigger heads and thus the entrance hole must be bigger and to keep the surface percentage of the hole within the required maximum the sphere needs to be bigger.

2)the amount of heat may melt your styrofoam, going bigger spreads the heat over more material.

3)your measurement may get your luxmeter out of range, a bigger sphere increases the range. But a ND filter before the sensor does that too.


Yeah, I didn’t want to write all that out. I’m lazy. Silly

Was the coating thick enough to keep the light from going through?

I was thinking of smearing Elmer’s glue on the interior surface and then pouring the powder on it and shift it around. That way you have a thick, jagged surface to help integrate the light.

Texas Ace Lumen Tube and JoshK Sphere calibrated with Maukka lights

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I cannot see images 2 & 3 in post #100.

This seems to always happen with images hosted with Google.

djozz
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Quote:
I was thinking of smearing Elmer’s glue on the interior surface and then pouring the powder on it and shift it around. That way you have a thick, jagged surface to help integrate the light.

That suggestion was done on CPF a few years ago, I think you refer to that. But unlike some other metal salts that are used for whitening, BaSO4 cristals are fairly transmissive for light, most light will actually enter the layer instead of being reflected by the outer surface. That is why to reach the maximum reflectance for bariumsulfate, the layer must be fairly thick, several mm. A single surface coating on top of a layer of glue will hardly do much, you will deal with the reflectance of Elmer’s glue more than with that single cristal layer of BaSO4.
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Sorry raccoon city, I don’t know what to do about that. Dealing with the whole image hosting fiasco, I’ve pretty much decided to just host from Google (though I’d like to hear if this really is a big problem for a lot of people not seeing the images).

Back to my sphere problem: What first tipped me off to my sphere reading too low on high lumen levels was when I measured my Sofirn SP40, Sofirn SD05 and my Astrolux HL01 (XP-L 4000k). I posted about it over in the SP40 thread, asked for other’s tested levels, and only got one (helpful) response. Basically all three of these lights (at higher levels) gave lumen numbers from my sphere that didn’t make sense. All three lights were measured on fully charged new high-drain cells (LG HG2). As seen in the SP40 thread post, my SP40 on Turbo only came out at 798 lumens. By eye I would have guessed it was putting out at least 1,000 lumens. My SD05 (on a fresh charged new Molicel P42A 21700) on high measured 2,223 lumens and on medium 792 lumens. General consensus on the SD05 (there doesn’t seem to be any authoritative measurements posted) is that it is putting out between 900 and 1,000 lumens in medium (which is a very solid stable regulated level) and +/- 2,500 lumens in high. My HL01 on turbo measured 1,030 lumens at start and 992 lumens at 30 seconds. I was expecting more like 1,200 lumens.

And now that I’ve stumbled on this issue some of my other measurements on other lights at higher lumen levels make more sense to be too low, such as my Convoy M1 XM-L2 driven @ 3.04A only coming out at 840 lumens. I also reviewed that Imalent BG10 XHP50.2 bike light which measured lower than expected at higher levels (which at the time I just thought was the manufacturer fudging #‘s).

So in that SP40 thread, YogibearAl measured his 4000k SP40 in his Texas Ace Lumen Tube calibrated with Maukka lights:
Low = 7 Lumens
Med = 65 Lumens
High = 358 Lumens
Turbo = 988 Lumens start up 963 @ 30 sec on freshly charged 30Q. Continues to drop as battery drains.

So I re-ran my lumen calcs based on YogibearAl’s posted #‘s above to compute a new multiplier. My previous multiplier was 0.4275, and now calibrating to Yogi’s #‘s I am getting varying multipliers, with the #‘s for the high outputs being significantly higher (my expectation – that my sphere is “good” at low outputs, but gets exponentially worse at higher levels). Multiplier’s I get:

SP40
Low – 0.4516
Med – 0.4422
High – 0.5000
Turbo – 0.5158

If I then run with the multiplier of 0.5000 from high mode, run that back against my SP40 measurements and also on my SD05 & Astrolux HL01 (XP-L 4000k) measurements, I get:
SP40
Low – 7.8 lumens
Med – 73.5 lumens
High – 358 lumens
Turbo – 934 lumens

SD05
Low – 324 lumens
Med- 926 lumens
High- 2600 lumens

Astrolux HL01
Stepped Ramp Levels:
Step 1 – 15.2 lumens
Step 2 – 51.3 lumens
Step 3 – 145 lumens
Step 4 – 190 lumens
Step 5 – 296 lumens
Step 6 – 472 lumens
Step 7 – 807 lumens
Turbo – 1160 lumens

So now my higher numbers seem more in line with expectations, but I suspect I’m showing lumen #‘s that are too high for the lower levels. My sphere was originally calibrated with the average of (3) Fenix HL55 headlamps averaging modes Low, Medium, & High (i.e. dropping Eco & Turbo), where ANSI ratings are Low = 55 lumens, Med = 165 lumens, High = 420 lumens, however I held Selfbuilt’s tested numbers which differed slightly from ANSI: Low = 55, Med = 161, High = 402.

I’ve now finished 4 coats of matte white paint on my new foam sphere halves. I quickly held up one of these halfs to the ceiling light (a standard lightbulb, LED 60 watt equivalent) and the outside of the foam no longer glows like the original sphere, so I think this has helped immensely in keeping light inside the sphere. I’m going to try to test this with a flashlight and luxmeter tonight comparing the lux reading through each foam (unpainted vs. painted). I still don’t have a piece of glass to use, so I’m not ready to assemble the sphere yet.

-Garry

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Wouldn't lining the interior with aluminum tape work better?

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LumenMax wrote:

Wouldn’t lining the interior with aluminum tape work better?


No, it should be white and as flat as possible, ideally a photon hitting the surface from any angle has an equal chance to leave again at any angle (so-called Lambertian reflection), that is key to the integrating properties of an integrating sphere.
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djozz wrote:
LumenMax wrote:

Wouldn't lining the interior with aluminum tape work better?

No, it should be white and as flat as possible, ideally a photon hitting the surface from any angle has an equal chance to leave again at any angle (so-called Lambertian reflection), that is key to the integrating properties of an integrating sphere.

 

So, why not paint the interior with a flat white acrylic paint to mimic ceilings vs an ideal laboratory condition? I get that companies want the best possible ratings for their products.

djozz
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LumenMax wrote:

djozz wrote:
LumenMax wrote:

Wouldn’t lining the interior with aluminum tape work better?


No, it should be white and as flat as possible, ideally a photon hitting the surface from any angle has an equal chance to leave again at any angle (so-called Lambertian reflection), that is key to the integrating properties of an integrating sphere.

 


So, why not paint the interior with a flat white acrylic paint to mimic ceilings vs an ideal laboratory condition? I get that companies want the best possible ratings for their products.


You could do that. For a discussion on integrating spheres you could follow the links in my sigline to some posts that I wrote on my journeys towards a working sphere. A very nice read on integrating spheres in general, if you are into that, can be found here: https://www.labsphere.com/support/system-product-brochures/tech-guide-a-...
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So I ran those checks on “light leakage” between my old unpainted sphere and the new painted half round foam. The pained foam (4 coats now) is definitely blocking light! I took my Convoy M1 XM-L2 (high at 3.04A) pressed it right against the foam on the inside and placed the luxmeter sensor right against the foam on the outside directly across from the light. Here are the results:

Unpainted foam
Low – 4,280 lux
High – 12,920 lux

Painted Foam
Low – 118 lux
High – 337 lux

Some pics (painted foam is the one where the light looks yellow):

My dilemma now is how to mount the luxmeter. This time I’m going to put the sensor hole 90º away from the light input hole. I’m going to open up the sensor hole completely to the inside (the wall is now painted, so I pretty much have to). I can either mount the sensor directly at the hole (the face of the sensor will be set back from the inner sphere wall since I can’t get it fully into the foam without some extreme cutting), use PVC pipe to “couple” the sensor to the sphere wall (inserting the PVC until it’s flush with the inner wall and painting the inside of the PVC matte white also) using either straight pipe, a 45º bend, or a 90º bend. With the bends I’m guessing I may get away without using a baffle inside the sphere. I’m concerned though about light reflecting off that PVC even with it painted matte white except maybe in the case of using a piece of really short straight piece of PVC. Any thoughts on this? Some mock up pics:

90º Bend:

45º Bend:

Straight Section:

By the way, anyone looking for glass like I have been, search for “clock glass” in order to find various size round flat glass that is readily available and doesn’t cost an arm and a leg.

-Garry

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Still working on my new sphere (slowly). I happened to take my company truck to get a new windshield installed and they were able to cut me glass to size, so I got (2) 4 1/2” diameter pieces for $5. Now I’m struggling with what to do about a baffle. I think I read that it’s best if the baffle is made of the same material as the sphere, or at least has the same coating. So I’ve picked up a flat piece of this same “smoothfoam” and have painted it matte white on all surfaces. This material is about 23mm wide, so it’s kinda big (thick). I was thinking to mount it using small wood dowels glued into the baffle and into the sphere (dowels painted matte white as well). My biggest problem is coming up with the proper shape/size. I think I read somewhere that light should reflect at least twice before reaching the sensor. Well if this is the case it seems you’d need quite a large baffle, because you’re not only blocking direct light from the entrance hole, but also beams from that first reflection. Also with the sphere surface being round (and hence a “sphere” – lol), you’d have to block from numerous directions.

What about this idea for a baffle?

Or is this layout preferred? This seems to be the more common approach. And is the 2nd baffle necessary?

Will it matter how close the baffle is to the sensor? Obviously I won’t put it extremely close, but is there a point where it’s too close and affects the luxmeter sensor’s readings adversely? Any help/guidance is appreciated!

Thanks,
-Garry

My Bike Lights Thread, Optics (TIR) Comparison Beamshots, Diffusion Techniques

, MTBR’s Lights & Night Riding Forum
NOTE: Now hosting my photos from my Google account. Post up if you can’t see them. Older photos hosted on Photobucket or Flickr may disappear (PM me if you want access to them).
jon_slider
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@garrybunk
I cannot see your pictures

good luck with your sphere

WTB Novatac Pocket Clip

garrybunk
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jon_slider wrote:
@garrybunk
I cannot see your pictures

good luck with your sphere

Aarrgghhhh! I wonder how widespread this issue is (percentage of people that can’t view my photos). I finally settled on using Google to host my pics (I wasn’t happy with alternatives I found and Google is super simple to utilize) and now run into people not seeing them. This might be better suited for a new/different thread rather than being discussed here.

-Garry

My Bike Lights Thread, Optics (TIR) Comparison Beamshots, Diffusion Techniques

, MTBR’s Lights & Night Riding Forum
NOTE: Now hosting my photos from my Google account. Post up if you can’t see them. Older photos hosted on Photobucket or Flickr may disappear (PM me if you want access to them).
JasonWW
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I can’t see any pics in #115 and #116.

The baffle is just to prevent direct light and should be opaque.

Texas Ace Lumen Tube and JoshK Sphere calibrated with Maukka lights

Click this to go to signature links. I'm still around, just not reading many new threads.

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Ok, I finally see the issue by using another browser on my phone. I’ve looked in Google Photos for sharing settings, but don’t see anything to change. And googling the issue doesn’t lead to anything helpful. Guess it’s back to the drawing board for photo hosting.

-Garry

My Bike Lights Thread, Optics (TIR) Comparison Beamshots, Diffusion Techniques

, MTBR’s Lights & Night Riding Forum
NOTE: Now hosting my photos from my Google account. Post up if you can’t see them. Older photos hosted on Photobucket or Flickr may disappear (PM me if you want access to them).
garrybunk
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JasonWW wrote:
The baffle is just to prevent direct light and should be opaque.

Ok, any ideas on a material to use that’s stiff enough to stay in place? And I guess styrofoam is not a good choice.

-Garry

My Bike Lights Thread, Optics (TIR) Comparison Beamshots, Diffusion Techniques

, MTBR’s Lights & Night Riding Forum
NOTE: Now hosting my photos from my Google account. Post up if you can’t see them. Older photos hosted on Photobucket or Flickr may disappear (PM me if you want access to them).

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