20 mm LED Lenses - Not All the Same

redfishbluefish · May 2, 2018

You would think that any and all 20 mm lenses at X number of degrees would all be the same. Well they are not!!!! This would make purchasing lenses just that much more difficult. You don't know what you're going to get!

Here's my story. I don't have a PAR meter, but do have a LUX meter. I measure the LUX with the unit turned up to 100% and get a maximaum reading of 42-43 thousand lux. On a second fixture, set the same way, with supposedly the same lenses, a reading of 16-17 thousand lux. WHAT! A close inspection of the lenses found the high lux lenses to have very little light coming out the sides of the lenses, while the low lux lenses were glowing light out the sides. My phone camera really doesn't capture it well, but here's what I got:

High Lux lenses:

Low lux lenses:

The red, blue and green LED's looked like miniture little cakes with colored icing....glowing in their respective color.

So to verify it was the lenses, I hung a fixture over the coffee table and fixed the length to the lux meter by placing it on a bin. This allowed me to move the bin (with meter on top) and take readings until I got a maximum. The meter was at 11 inches to the face of the fixture.

I got a maximum lux of 43.5K.

The same fixture was used, and I replaced the lenses with the "glow" lenses and repeated the measureements, this time finding a maximum lux of 17K lux.

So be careful purchasing replacement lenses.....especially from no-name suppliers.

dbl · May 2, 2018

Very interesting Paul. Thanks for sharing your findings.

mcarroll · May 3, 2018

redfishbluefish said:
The meter was at 11 inches to the face of the fixture.

If you measure the individual emitters with the "glow lens" does it still measure with the same spread as the "high lux"?

At 11", assuming your lenses are supposed to be 90º, that would mean a spread (diameter) of 22". (other lenses need a little more calculating....90º is easy math)

I think lenses are calculated according to FWHM though aren't they?

The angle inside which you get at least half the max. intensity of the light? I guess by whatever standard, do the different lenses measure the same coverage gradient with your meter, but just with lower intensity?

I'm wondering if you got defective lenses, or if you got (e.g.) 120º lenses when you were supposed to get 90º's or 60's or whatever else.

I know if you mix up your bags of lenses you may as well just put them in the recycle bin cuz you can't tell the difference between most of them without hooking them all the way up to take FWHM readings on each. one. of. them. ;Vomit So if anyone in the chain of custody of your lenses had a mixup....say a return order going back into the wrong parts bin....well you get the idea.

2¢

redfishbluefish · May 3, 2018

Matt, you certainly could be right about mixed up lenses. The way they were sold (in all fixtures) were 39 90 degree lenses and 16 120 degree lenses. I have no way of testing this, but certainly, some of the light "lost" could be from wider angle lenses being used. However, I think (my opinion) the majority of light lost is by it passing out the translucent sides of the lenses, while in the "non glow" this light is being reflected out the face of the lens. The photo above doesn't capture this amount of light, but in person, it's quite substantial. Interestingly, when mounted in the canopy, the "glow" lens fixture is in the middle. Note the light on the back wall of the canopy. The glow fixture is casting a nice bit of light up the back of the canopy. All three fixtures supposedly have the same lenses.

70% Blues only:

70% Blue, 40% White:

I don't believe the lenses are defective. I believe what happened is that the manufacturer changed suppliers, thinking that a 90 and 120 degree lens is a 90 and 120 degree lens. I think it's more than the angle of the lens that goes into the light coming out....what I'll call the reflective quantity. In the case of the glow lenses, very little reflective light.

Here's the bottom line.....the retailer is making good on providing all "non-glow" lenses! I'll know in a week or so.

chipmunkofdoom2 · May 3, 2018

I noticed something very similar with two different black boxes, a Vipar Spectra and a Galaxy Hydro. The Vipar Spectra produces about 500 - 600 PAR at 100% blue and 20% white, measured 14" below the fixture. The Galaxy Hydro at about 40% blue and 20% white (per the knobs on top) measures the same PAR at 12" below the fixture. Either the diodes are significantly different between the two fixtures (they don't appear to be), or the optics are different.

redfishbluefish · May 3, 2018

Chipmunk, take note of the light coming out the sides of the lenses....that is the tell-tale sign with the lenses I have. The non-glow, this light coming out the sides was negligible.

redfishbluefish · May 14, 2018

My replacement lenses arrived and they were installed and tested and I'm back in business with lux comparable to the other two fixtures.

It still amazes me that by outward appearance these lenses look pretty much the same, but one set provided only 39 percent of the light (Lux). Here is a side by side picture of the two sets.

The "good" set is on the right (off-white), and the "bad" set is on the left (white-white). Other than the slight color difference, the only other thing I notice in closely examining these lenses is that the good set, the clear lens appears to be more silvery looking and the frosted lens appears slightly more frosted. Otherwise they appear to be similar 20 mm lenses. It just boggles my mind that one set, although looking very similar, only produces 39 percent of the light. Buyer beware!

mcarroll · May 27, 2018

redfishbluefish said:

Hard to be sure from the pics, but the lenses on the left (bad lenses) also appear to be able to fit a larger bead size than the ones on the right. Even if that's only an illusion from looking down through the lens in the pic, that's at least one additional way the lenses do in fact look different. (Mostly comparing the two non-frosted ones, which means the right-hand lens of each group.)

redfishbluefish · May 27, 2018

Matt, your post caused me to look at the bottoms of the lenses very closely, for the first time. My guess of what you're seeing is my haphazard placement of the lenses, with the slots not all going in the same direction. So the bottoms, the openings appear to be the same size. The only noted difference is that the slot on the "bad" lens goes all the way through, to the sides of the lenses, while the "good" lenses, this small portion is filled in.

mcarroll · May 27, 2018

(I dunno if you're as curious about this as I am since the problem has already been solved, so fee free to stop me....but in case you are...

)

If you pop the lenses out of their holders so you can see only the clear piece, do they still seem pretty identical?

redfishbluefish · May 27, 2018

I've never "popped" out a lens....and they don't appear to pop easily. I'm guessing they are glued in??? Can't get them out. Closely looking at the lenses, they appear to be very similar. I know this picture isn't going to offer much, but here they are:

So the lenses look very similar, but the side sleeves are were the difference was notices. When lit, light illuminates the "bad" lens sides....they glow. The "good" lenses, the sides allow very little light to come through.

mcarroll · May 27, 2018

Interesting, but still not clear why it's happening is all.

Since we have to guess, I'd say the sides of the lens in the "bad" one are not matte finished (or whatever finish is done) to make the lens exterior reflective. A la the jargon phrase "total internal reflection" or "TIR".

I guess it was a pain to have to run into this, but it was interesting at least as much as mysterious.

mcarroll · May 27, 2018

(my lenses have always been snapfit, I have not handled that many different lenses so I wouldn't necessarily know what's common. )

redfishbluefish · May 27, 2018

I have no idea what the significance might be, but there does appear to be a difference in the lenses.

I was looking at the lenses and holding them up in front of me, with the computer close by. When the "good" lens is about an inch from a white portion of the computer screen, it clearly looks like a window screen....reticulated....and fully filling the circular portion. Couldn't really get a good picture...this is the best I could do.