comparing output via the ceiling bounce

[superflytnt]

What's up folks.................I've been catching a bit of grief about this and was just curious if anyone else uses this method. In the LED forum I was comparing the brightness between the Streamlight Microstream and Fenix LOD (on medium) by pointing them both at the ceiling (about 6 inches from it) and blinking them back and forth while looking at the floor to see overall reflected light. I was slammed by a couple of members who said that the MS has a bit tighter spot and that it skews the results in it's favor. At 6 inches? These lights both have a hotspot...............am I wrong that these are similar enough beam profiles to compare using this method? Does anyone else out there use the ceiling bounce method to compare overall output? I thought it was kind of a poor mans standard but if you'd if you believe them it's all but useless......................

 

[BlueBeam22]

As silly as it sounds you might want to try shining both lights one at a time into the reflector of a light with a huge reflector as this will completely scatter the light from each flashlight in random directions so you will see which one really lights up the room more and puts out more light. I just tried this method and found it to work well.

 

[The Sun]

i do the same thing. its just too hard to tell sometimes just based on the hotspot of a light. a 120lm light can be just as bright at the hotspot as a 200lm light half a meter/yard from a white wall, but the overall brightness (spill, spot, everything) is where i can tell the difference (sometimes). i don't have an expensive light meter so i gotta do the best i can. right on brother!!:thumbsup:

 

[BlueBeam22]

i do the same thing. its just too hard to tell sometimes just based on the hotspot of a light. a 120lm light can be just as bright at the hotspot as a 200lm light half a meter/yard from a white wall, but the overall brightness (spill, spot, everything) is where i can tell the difference (sometimes). i don't have an expensive light meter so i gotta do the best i can. right on brother!!:thumbsup:

:thanks: It really is a great method, I was just doing this with my Coleman 530 lumen LED spotlight and my 1mcp Vector spotlight which usually beats the Coleman due to its bright hotspot, but shining them into the reflector of my giant 17mcp spotlight the Coleman beat the Vector in lighting up the room more.

 

[jzmtl]

What's up folks.................I've been catching a bit of grief about this and was just curious if anyone else uses this method. In the LED forum I was comparing the brightness between the Streamlight Microstream and Fenix LOD (on medium) by pointing them both at the ceiling (about 6 inches from it) and blinking them back and forth while looking at the floor to see overall reflected light. I was slammed by a couple of members who said that the MS has a bit tighter spot and that it skews the results in it's favor. At 6 inches? These lights both have a hotspot...............am I wrong that these are similar enough beam profiles to compare using this method? Does anyone else out there use the ceiling bounce method to compare overall output? I thought it was kind of a poor mans standard but if you'd if you believe them it's all but useless......................

I think those who slammed you are doing selective reading and completely skipped the part about looking at the floor instead of ceiling. Measuring diffused and reflected light is how integrating sphere works and I don't see how shining light at ceiling while looking at floor is any different.

 

[superflytnt]

I think those who slammed you are doing selective reading and completely skipped the part about looking at the floor instead of ceiling. Measuring diffused and reflected light is how integrating sphere works and I don't see how shining light at ceiling while looking at floor is any different.

LOL, I wish that was the case but I specified exactly how I did it while we were "discussing" the method. Some folks just take offense if you say anything that they think is negative about one of their favorite lights, even if it isn't meant that way. I own both lights in question and like them both but I'm still a pragmatist. If one light does something better than another I'll accept that.

 

[Stillphoto]

After I had read about the technique that's how I've been comparing. I personally feel its more practical than staring at bright spots on a wall.

Best usage of this so far has been with my new peak pacific. I've got two different battery tubes for it, and two noticeably different outputs. The hot spots seemed similar, but the room bounce told the tale.

 

[Rob187]

I recently did a few comparisions using the ceiling bounce method and a light meter. I was careful not to move the light meter between tests and ensured each light was in the same place and the beam aimed at the same spot.

I think that if the sensor is directly underneath the point where you aim the beam, a light with more throw, i.e. a tighter spot does give a higher lux reading than a light with the same overall output but a broader beam.

However, it remains the best way I know to compare overall output of lights without proper scientific testing.

It's just for fun after all.

 

[kramer5150]

FWIW... I do the same thing, except I spread a white bath towel across the floor, in an effort to remove the reflective "glare" from the ceiling and floor tiles. I evaluate light levels A/B by looking at the amount of light emitting off the towel.

 

[Bullzeyebill]

I've been using ceiling bounce with a light meter for a few years now. Some of our CPF'ers who have made their own lightboxes, also do bounce with a light meter, and have similiar results. It is a quick portable way to compare lights. Make sure that room environment does not change, and keep lights and meter at same distances from each other, and ever so often re check the environment with a light with a known output, for a baseline.

Bill

 

[Marduke]

Lights with a tighter hotspots and less spill will reflect more light directly downwards due to the lower incidence angle. Floodier lights with a higher average indicence angle will diffuse more light outwards, and by the time so much lights reflects off a much greater surface area, it appears dimmer.

A ceiling bounce can be immensly useful, and is much better than just shining two lights on a wall to compare total output, but the results can be just as deceiving if you don't consider the pros and cons of the method you are using.

 

[TONY M]

Lights with a tighter hotspots and less spill will reflect more light directly downwards due to the lower incidence angle. Floodier lights with a higher average indicence angle will diffuse more light outwards, and by the time so much lights reflects off a much greater surface area, it appears dimmer.

A ceiling bounce can be immensly useful, and is much better than just shining two lights on a wall to compare total output, but the results can be just as deceiving if you don't consider the pros and cons of the method you are using.

Very true Marduke. When I compare my lights I shine them into a ceiling light with a diffuser in a room with no external lights and photograph them in exactly the same way, that way it does not matter if one light is more throwy than another. I have tested this with putting diffusers over the lenses of throwy lights and doing the test again and it makes no difference.

When using the ceiling bounce method the tints of the lights can make it difficult to see things accurately so I set my camera to a manual WB setting and desaturate them to compare.

 

[superflytnt]

Lights with a tighter hotspots and less spill will reflect more light directly downwards due to the lower incidence angle. Floodier lights with a higher average indicence angle will diffuse more light outwards, and by the time so much lights reflects off a much greater surface area, it appears dimmer.

A ceiling bounce can be immensly useful, and is much better than just shining two lights on a wall to compare total output, but the results can be just as deceiving if you don't consider the pros and cons of the method you are using.

I still don't agree with this. As I stated in the LED forum thread and my original post here, I hold my lights at the most 6 inches from the ceiling. The beams from the two lights in my original post, the LOD and Microstream, appear to have essentially the same beam pattern at this short distance. If anything, at this range more of the tighter spot should be blocked by my big ol' ham of a fist than that of a floodier light LOL (although I do turn them at a bit of an angle to avoid just that :thumbsup............................

I also catch alot of the reflected light on the walls out of my peripheral vision so it's not like I'm just staring at the spot on the floor exactly opposite the ceiling. It still seems to me that reflected light is reflected light so if a beam has brighter spill instead of more of a spot then that will reflect also. Like someone else pointed out, aren't lightboxes just a form of the same thing for the most part? I wish that I had a zebralight to test this out but I just don't own any truly floody lights? Oh well, it works for me so what the hay......:twothumbs

 

[Marduke]

It still seems to me that reflected light is reflected light so if a beam has brighter spill instead of more of a spot then that will reflect also. Like someone else pointed out, aren't lightboxes just a form of the same thing for the most part?

No, and no. A lightbox or integrating sphere works a bit differently, and the entire internal surface is of uniform reflection. A well designed lightbox has the location of the light meter chosen VERY carefully to avoid the aforementioned affects.

But w/e, if you don't want to learn something new, that's your loss and other readers of this thread gain.

 

[wechnivag]

Keep in mind that our eyes will adjust to the ambient light level by opening and closing the iris. Kinda tricky to keep a 'calibrated' sensitivity of the eyes...

So if you are comparing two lights, and you happen to look at the hotspot while switching between them (can be tricky if you have a multimode reverse clicky on on hand, and a forward clicky on another), then you might be 'recalibrating' your eyes between comparison of the ceiling bounce...

Just a thought...

 

[Bullzeyebill]

Keep in mind that our eyes will adjust to the ambient light level by opening and closing the iris. Kinda tricky to keep a 'calibrated' sensitivity of the eyes...

So if you are comparing two lights, and you happen to look at the hotspot while switching between them (can be tricky if you have a multimode reverse clicky on on hand, and a forward clicky on another), then you might be 'recalibrating' your eyes between comparison of the ceiling bounce...

Just a thought...

That is the reason I added in a lightmeter for my ceiling bounce tests. Not perfect, but it beats my "calibrated eyes".

Bill

 

[h2oflyer]

I sort of agree with Superflytnt. I read a post somewhere about using
ceiling bounce as a means of comparing total light output.

When I got my BitZ , I wanted to compare it with my NDI Silver and
used small bathroom with flat white ceiling - lights on 30in. counter-
use comic section of newspaper on floor to compare readability,I judged
them to be the same.

I later read a post on BitZ review where someone with measuring equip.
got 130 for BitZ and 133 for NDI.

 

[Bullzeyebill]

I sort of agree with Superflytnt. I read a post somewhere about using
ceiling bounce as a means of comparing total light output.

When I got my BitZ , I wanted to compare it with my NDI Silver and
used small bathroom with flat white ceiling - lights on 30in. counter-
use comic section of newspaper on floor to compare readability,I judged
them to be the same.

I later read a post on BitZ review where someone with measuring equip.
got 130 for BitZ and 133 for NDI.

Good for you. Now go buy an inexpensive light meter and do the same tests. Good for comparing output and also good to see what type of circuit you are using, and if it is constant current or not. You can also see if heat is effecting the light output, and other issues you can evaluate.

Bill

 

[superflytnt]

Good for you. Now go buy an inexpensive light meter and do the same tests. Good for comparing output and also good to see what type of circuit you are using, and if it is constant current or not. You can also see if heat is effecting the light output, and other issues you can evaluate.

Bill

Yeah but, as I said in the OP, I consider it the "poor mans" method. If I need a fricking light meter to tell the difference where my eyes cannot then I don't care about that difference LOL. If they look the same to my eyes then I'll consider them the same. I'm not going for bragging rights here, just useability.

I know, I know.............it takes 4x the amount of light to see a 2x increase with the naked eye but I've been doing this for quite awhile and have a pretty good eye for output levels. I can tell the difference between 2 and 5 lumens, 5 and 10 lumens or 20 and 30 lumens easily. 70 to 80 gets a bit tough, 120-130 is tougher still.

Point being that I was comparing two lights in the 20-30 range and it's pretty easy to tell which one has more output using this method....................at least for me

 

[eebowler]

I've never noticed differences between spot lights and flood lights (with similar outputs) but then, the beams of my lights don't differ very much. My method is involves shining the light from the floor to the roof or whatever height is required for ALL of the corona to be on the roof. From my simple tests, weather the light is 6 ft from the roof or 10 ft, as long as all of the corona is on the roof, the reflected light doesn't change.