reflector "size" question

[THE_dAY]

reflector \"size\" question

to keep this simple (i realized there can be so many factors), lets say we have two lights with same LUXIII and board running @1000mA. only difference is the reflector size: one has a 17mm and the other has a 27mm. what would be the difference?
i would assume the 27mm to have a brighter hotspot. so would the 17mm have more sidspill? and if both lights were meaured for total light output, would they be equal or would the bigger reflector have the edge?
thanks in advance /ubbthreads/images/graemlins/smile.gif

 

[NewBie]

Re: reflector \"size\" question

It also depends on reflector depth.

 

[THE_dAY]

Re: reflector \"size\" question

so lets take the Mcgizmo reflectors for example where the 27mm is bigger and deeper than the 17mm version. i basically would like to know if total light output is the same since it is the same LED @ same current. thanks

 

[McGizmo]

Re: reflector \"size\" question

Since reflectors are not 100% efficient, max light output will be achieved with a bare emiter and no reflector or window in front of it. If you have two reflectors based on the same parabolic curve, the deeper the reflector is, the larger its diameter as well and the more light output is re directed by the reflector. The larger and deeper reflector will have a slightly tighter hot spot and the angle and intensity of light in its spill beam will be tighter and brighter as well. My 27 and 38 mm reflectors are based on the same curve. the 38 typically will yield a lux reading slightly in excess of double that of the 27 mm. The spot beam appears to be smaller in diameter (on the 38) because the additional light added to the spot, beyond that provided by the "first" 27 mm portion of the reflector is better collimated and concentrated in a narrower beam (with less divergence).

I would guess if both the 27mm and 38mm reflector were measured in an integrating sphere using the same LED and drive current that the 27 mm would score higher in flux (lumens). However, if you are after an optic package to yield more throw (lux) then the 38mm obviously surpasses the 27 mm.

In many "realistic" cases, efficiency will take back seat to the use and distribution of light that does make it out of the front end. I have some inefficient but excellent flood beam systems that provide excellent even and artifact free light and I could care less about the light being lost if it were to be added back in bright rings or other noticible artifacts or hot spots.

 

[THE_dAY]

Re: reflector \"size\" question

thanks McGizmo,
the 27mm would score higher than the 38mm? why would they not be the same if measured in an intergrated sphere. am i correct to assume that the 27mm would then have more sidespill light than the 38mm since the 38mm has most of its light in the hotspot. i am still learning so forgive me if these questions have been asked many times before.

 

[Reptilezs]

Re: reflector \"size\" question

the reflective surface doesnt reflect 100 percent of the light. the 38 mm has more reflective surface

 

[McGizmo]

Re: reflector \"size\" question

The 27 would presumably score higher because more of its light is coming out direct in spill and not reflected. The 27 will have a larger spill angle but the intensity of light within the spill may or may not be as great as that in the spill beam from the 38. Some reflected light is bounced from the orange peeled reflector at such an angle that it is not columinated with the majority but goes out into the spill region.

If 100% of the light from the LED is let out directly, it will all be measured by the integrating sphere. Light that hits a reflector will be diminished by the inefficiency of the reflective surface. Since the 38 mm reflector has more reflective surface, I assume that there will be a greater loss than in the case of the 27 mm. The amount of loss may not be significant or noticible but a loss, none the less.

 

[THE_dAY]

Re: reflector \"size\" question

thankyou guys, i now understand the concept of reflectors!