REVIEW: CREE MC-E Diving Light

[foglesre]

Thats 2.54mm.

Thanks for clarifying for me that this is NOT a dive light.
The W200 that is sold on DX has a 6mm thick lens and its 25mm or so wide. a 50mm lens would be under 4 times the strain at the same depth but this is less than half the thickness. So 1/8 of the pressure rating.
W200 is rated to 200 meters. Meaning this is probably rated to 25meters.
That is why it costs only $81

Well, I have to admit, 0.1 inches seems a bit thin, but I went ahead and ordered one anyway. I also decided to apply a bit of engineering to the problem. Now, I must admit, it's been more than a few years since I got my engineering degree, but here's what I came up with...

I found quite a slick little Excel macro shareware program called MITCalc that performs plate stress analyses. I treated it as a simple supported plate. The o-rings probably provide something between simple and fixed support.

I pulled mechanical properties of glass from EFunda. There was quite a range given and as I have no idea of the glass type, I chose mid-range numbers:

Modulus of Elasticity 65 GPa
Shear Modulus 28 GPa
Poisson's Ratio 0.24
Ultimate Strength 45 MPa
Radius 25.4 mm
Thickness 2.54 mm
Pressure 303 kPa (100 ft against strandard atmospheric inside the flashlight)

This produced a deflection of about 0.09 mm and a maximum stress of 37 MPa...not a lot of safety factor against the 45 MPa Ultimate Strength. As a fixed supported plate, the results would be 0.02 mm deflection and 23 MPa maximum stress. The properties of the glass are debatable, but I certainly wouldn't call the lens overdesigned for 100 ft depth.

By comparison, applying this anaysis to the W200, 25.4 mm diameter and 6 mm thickness, I come up with 0.0004 mm deflection and 1.6 MPa maximum stress (simply supported) at 100 ft, or hugely overdesigned. (And no it's not linear.)

I would certainly feel better if the light had a thicker lens. I haven't yet seen the light, but it would be wonderful if one of these would fit:

Borofloat® Lens

A 52.1 mm diamter, 6.53 mm thick lens is available. Not sure how much extra thread there is in the light to potentially accomodate an extra 4 mm thickness...

Would love to get feedback from someone who has doen a bit more mechincal design in the last 15 years than I have...

Bob

 

[Hatul]

It may not be the right light for heavy duty tech diving, but fortunately most recreational night diving is done in shallow depths, where this light is unlikely to implode.

Adam

 

[adm3745]

I own the SSC P7 version from Deal extreme. I have taken it to 144 ft so far with no problems. The lens does feel a little thin (2-3mm), but there is room to add another Lens. The only problem I noticed that could contribute to flooding:

The silver cap that screws the lens down becomes very loose at depth because the oring compresses. I noticed this quickly and tightened it at depth. Not doing this could cause it to unscrew and flood when you come shallow. I'll be taking it again to 120 ft for 2 more dives and I'll let everyone know how it holds up.

 

[Venus]

My CREE arrives last week, the SSC P7 from DealX $81
ok - I get a rubbish exchange rate, but it was still worth it

I shined it out of my window and it reached further than 200 meters down the road

I don't know when I'll take it in the water because my heated vest stoped working two weeks ago, and it's cold out here :depressed:

So if ADM3745 took his down to 50meters +
then this the CREE should be ok for Chuuk where the wrecks are in the region of 40meters
I was a little worried that the lens would crack, because people have mentioned the very thin lens

Are there any tips to using this light:

1) check the front bazel on descent and tighten if it becomes loose
2) ?
3) ?

 

[adm3745]

Hey everyone. I dove this light 2 more times. 117 ft and then 70 ft for 2 hours. It is still working fantastic. Again, I had to tighten the bezel. Hopefully it stays permanant this time. So thats 4 dives and still no problem. I'll do 4 more this weekend. If it makes it then I'll be convinced and buy a couple more.

 

[gcbryan]

If anyone does any mods on this light be sure to post it! Putting in a thicker lens, maybe better o-rings, and I wonder how hard it would be to turn the 5 mode switch into simply on (high power) and off?

 

[Venus]

This may be a really silly question, but here goes ...

If the o-ring compresses on the descent and you tighten the bezel
what happens on the ascent when, I assume, the o-ring uncompresses

does this weaken the o-ring if you leave it in it's expanded state with the bezel tightened
or, should you loosen it soon after surfacing when in a dry environment ?

I had to tighten the bezel. Hopefully it stays permanant this time

 

[gcbryan]

I would leave it tightened. You certainly shouldn't have to tighten parts of your dive light at depth. I don't have to do this on any other dive light.

I'm just wondering if it shouldn't perhaps have better o-rings and a thicker lens of course.

 

[Hatul]

I own the SSC P7 version from Deal extreme. I have taken it to 144 ft so far with no problems. The lens does feel a little thin (2-3mm), but there is room to add another Lens. The only problem I noticed that could contribute to flooding:

The silver cap that screws the lens down becomes very loose at depth because the oring compresses. I noticed this quickly and tightened it at depth. Not doing this could cause it to unscrew and flood when you come shallow. I'll be taking it again to 120 ft for 2 more dives and I'll let eve


Are you sure it's an Oring and not a gasket? Usually O rings do not rely on tightness but are self sealing.

Adam

 

[adm3745]

It is an oring. THey are made of silicone and are very squishy. Better Orings would definately be a good upgrade. It is self sealing, but it does compress too. I'm going to leave mine tightened now for awhile and see what happens. If people are interested I can take some very detailed pics of all the different components.