Focusing Lens Question

Hi,


I am designing a hand torch, it will have 3 different light sources as : White (6500K), Blue(470nm) and UV (370nm).


My white source is composed of 2 chip leds, blue source: 6 chip leds and UV source: 4 chip leds, all different colors mounted on a MCPCB of its own. Leds are about 3 mm apart from each other in rectangular or square matrix.


I use the same lens set for all colors, which consists of collimator and focusing lenses.


My problem is this:


The torch was measured using an integrating sphere both with and without lens set. The lens seems to drop my radiant flux output:


From 4W to 0,9W for white light.
From 3W to 0,6W for blue light
From 1,8 to 0,5W for UV.


I had expected some loss due to the lens but not this much. The inner walls of the lens assembly are naked aluminum and not covered with reflective finish. I am an electronics engineer and my optics knowledge is pretty non-existent so I would greatly apreciate if someone can tell me if this ratio is too much due to bad design or normal for a standart lens assembly?


Best Regards

that is quite an experiment. Yes you are going to see significant loss with a focusing lens although the white light loss is pretty surprising. This is the first time I have heard of some one doing all this with a focusing lens. Any specific reason you want to use the focusing lens?

I might have used the wrong word for the job lens aims to does. The design consists of 4 lenses which aims to first first collimate the light and then project it in such a way that it is a circle of certain diameter at a certain distance and can be adjusted to change the size of the circle.