LED spots for lightening a sales Hall – part 4 of 4 – the shadow and the diffusion disc

In the last part of the Blogreihe (part 3) , I explained what driver I for this project (what is it?) have taken and what options I have to influence the light cone. Now only the question arises, what should I build?

LED spots for lightening a sales Hall - part 4 of 4 - the shadow and the diffusion disc

The customer will continue in the development included.

So I drove with all the information in the clothing business and have presented my findings and developments of the management. I have to admit this is really fun to present something home and then have to explain what I did anyway and why and why and why it now as it is. I can recommend at this point everyone: enthusiastically you yourself for something, which investigates, studied, accumulating knowledge and then you can teach yourself other interested parties. That is really fun!
Back to the topic. After I had explained everything, we have obtained an extension cord and tested the LEDs. Everyone was quite excited, how much light can come from a 10 W LED. So far, they know only 10 W chips from China which had only an efficiency of about 50-60 lumens per watt, and were installed in the small floodlights. This one twice from the same electrical energy could get out with good quality, almost no one believed until he saw it. And the same they have been also the request check.

Matching with the vicious

  1. Could the LED show the customers?No, only if you look directly upwards.
  2. Brings light output enough to the LED?Yes, definitely!
  3. Is the cold white lighting was the correct decision?Yes, the clothes have properly started to shine and the reflector strips were very good to see. The CRI value is also sufficient.
  4. Shadows (which was now something new)?”Look, the shadow on the wall is clearly too hard.”OK it is now also an afterthought I noticed. If you look at the shadows on the wall, then the transition from shadow to the illuminated surface of the wall is only a fraction of a millimeter wide. That was definitely not good for the optics. Here should be rectified yet.
  5. Beam angle, push-on lens or COB lens?Here are divided, but the majority was for the clip-on lens, because here the cone of light rather “expired” and not hard was delineated.

Conclusion: I’m definitely on the right track!

A sharp shadow shows up as a new challenge

Arrived back home, I had to figure out so, how I can eliminate these shadows. What is it actually that the shadow is so sharp? Here comes the optical physics in the game again. A LED is a point light source. So, all light beams emanating from a point. The smaller the point, the sharper are the shadows. Compare, you can very well with a solar eclipse. The Sun is a huge light source, the Moon of shadow donor. The Umbral shadow is so small and the Penumbra, so the transition area quite wide. The next the shadow of the canvas is away, the greater is the Penumbra. If the Moon was now very close to the Earth, the Penumbra would be also much smaller than the core shadow.
Continue forward to hang the clothes is impossible. The LED not goes back also, so the only way is to increase the magnification of the beam area led the Penumbra. Because I so not able to increase the LED, you need another solution.

A diffusion disk puts us on the right track

I got the idea to use a diffusion disk. Is a still illuminated from behind, lights them up evenly and in turn emits light. The radiating surface is therefore greater. However, the disadvantage is that a still absorb up to 50% of the light. It is then no longer to the lighting of the display available. 50% light absorption but also means that the washer pretty hot is. If the LED would now be conducted with 12 W, 10 W of electric power into heat directly to the LED would fall off. 2 W were in there in the light photons. If now the frosted absorbs 50% of the light, the performance must drop somewhere. And as is so often the case in nature, energy is converted mostly into heat. Simplified one could say that the frosted with 1 W of thermal energy is heated. That would not be good, because so much energy the Plexiglas could begin to melt.
So, I have searched on the Internet for a such diffusion disc and am struck it rich at Laserpoint 24 h. The owner told me that he can produce clear plexiglass-sheets and can relate them with a matte foil. This would have the advantage that more light through. The efficiency of the plate better. The light transmission of such disc at about 75-90% would be appreciated. More accurately he could not tell me, because he himself had no experience in this area.
So I myself used it and tested different frosted films on the plexiglass-sheets. It was blatant that a film is so strongly has heated up, that she even burned! Because you can see times how extremely much energy inside the light and that you not rum should fool around with 2 W light energy. Incorrect use it could be also here the fire. No fire due to short circuit, but a fire by photons. (with 2 W laser light can be cut easily by styrofoam)
After trying a bit I but find the right film and each LED can be equipped with such a slice of diffusion. The shadow was not so tough and the management was thrilled! After about 6 months of development I finally managed to develop a functional LED light with all necessary requirements.
A similar purchase solution in this area would cost less than around €75. While the efficiency of my is LED by approximately 20% better than current purchasing solutions. I can be really happy!
Technical data:

  • 1,05 A in 24,24 V result 24,62 W per LED
  • Lumen:1450 according to data sheet
  • With diffusion plate: 1270 lumens at 90% light transmission.
  • Efficiency:103 lumen/Watt (with Diffus or plate – calculated)
  • Efficiency:118 lumens/Watt (only LED without diffuser Panel according to data sheet)

Conclusion: do-it-yourself solutions are better than the current buying solutions of the industry though time consuming in the development, but still a lot.
So goes this article series come to an end, I hope you had to accompany me ß during this development over the last four weeks of Spa. One anticipated: already some time has passed between this project and the online job of posts. There are now already first long-term experience with these lamps in the daily use of duration of – but I’m going to tell that in a further contribution.

All parts of the series of articles in overview

  • Part 1: The order and the first considerations and plannings
  • Part 2: The choice of LED and of the correct heat sink
  • Part 3: Housing, lens and costs
  • All homebuilt lamps at a glance