You need an unobstructed light source. No lens no reflector to get a crisp shadow at that short 10-15cm distance. What we call a zoomie flashlight comes close but not at the short distance. I now tried a flashlight with no lens and no reflector and it casts a nice circle of light and has very crisp shadows of my hand on the ceiling, closer and further away than your requirements. You should be able to get it close to just the size of the steel plate.

The all-dielectric type consists of two highly reflecting mirrors separated by a dielectric spacer layer. These reflecting mirrors are constructed of alternating high and low refractive index materials and the reflectance of the stack is sometimes in excess of 99.99%. By varying the thickness of the spacer layer and or the number of reflecting layers, one can alter the central wavelength and bandwidth of the filter. This type of filter displays very high transmission in the passband, but, has a limited range of out-of-band blocking. To compensate for this deficiency, an additional blocking component is added, which is either all-dielectric or metal-dielectric depending upon the required blocking range. This additional blocking component will eliminate any unwanted out-of-band radiation but it will also reduce the overall throughput of the filter.

Band passfilter calculator

What I’ve tried: Cheap chinese Creee Q5 torches give me quite a nice light and crisp shadows, but I obviously cant hook this up to the mains. 0.5w strawhat led. Perfect light - way too dim 10w COB floodlights- Perfect brightness. Weatherproof. Unfortunately, they cast a fuzzy shadow. 3030 superblock 1.4w 120 lumen module. A bit fuzzy and a bit too dim.

My problem: I need the smallest pinprick of light of the highest lumen output in order to cast a crisp shadow. It needs to be suitable for exterior use too. There are many light sources that will give me a blurry shadow, but very few that make it crisp. It really needs to be a tiny, naked light source, as far as I can tell. I would love to find some off the shelf product that would suit, but would also consider building something - or working with someone experienced who could make something bespoke for me.

Band passfilter graph

Thanks Lexel, I really appreciate your help. That sounds good. Is that easy enough for a novice to put together do you think, or should I find someone experienced to put it together for me?

Thanks Firelight2. That’s pretty much what I’ve gleaned from scouring the RS catalogue. I suppose I was hoping for some existing ready made solution that would fit the bill. The lighting feature is to be mounted externally on a nature reserve visitors centre wall. It’ll be eventually wired up by a registered electrician, but I’m wary of dabbling with leds/electronics that are way out of my experience for something that’s going to be in the public realm. Is there anyone you could recommend who could provide/build what I need?

Band passfilter applications

The project: I’m making laser cut steel panels with botanical designs cut in to them. These will be sconces/shades fixed to an exterior wall through which I want to shine a light so that the cut out pattern will be projected on to the floor. Essentially they are big steel lampshades, likely to be around 60cm x 40 cm. They will be around 10-15cm from the light source.

It’s a festoon bulb to fit car number plates or reading lights. It claims to be 250 lumens and is in fact incredibly bright. The tiny single emitter means that there is almost no blurring of the shadow on the floor. I can house it in a waterproof case and use standard car bulb fittings. However, I need a bit more oomf! I think that I could really do with 400-500 lm.

If it helps anyone: this reflector-less kind of light is commonly called a “mule”. I’d have my C8 like that, but without the reflector there’s nothing holding up the lens, and I’m not a fan of such blatantly-vulnerable hardware :confounded:

Thanks Lexel. Those links are interesting. I’ve wondered if adapting torches might be a possible solution. I’d probably be driving 5 or 6 of these in total, so am assuming that I can just do the maths and get a driver that delivers enough power to each for my needs. Weatherproofing is my other concern, but I’ve seen some ip67 cases that may work.

All of our bandpass filters are stabilized to prevent drift of peak wavelength with age and are hermetically sealed for maximum humidity protection. Each filter is mounted in a black anodized aluminum ring which affords increased protection against damage resulting from rough handling and moisture penetration. However, even with this construction, it is advisable to avoid prolonged exposure to environments in which high humidity and large temperature variations are concurrent.

Dedomed Cree XPG2 or XPE2 might be an option for very small emitters, but not something for a beginner, need to reflow on DTP for the XPE2

Perhaps take the glass and reflector out of the 10W flood and see what happens. I have a couple 12V 10W in warm white here if you need me to give a try. No cool white on AC current here at home. I think the fuzzy shadow is from the glass reflecting back on the reflector and mimicking multiple light sources. If it works and you need brighter go with 20W. These lights are over rated so even a 20W is only about 13W actual.

I see no problem taking a flashlight with a really short reflector and replace it with a spacer. Or one to replace a lens with glass.

You can drive the light with a buck driver like this set to 4V, or replace the driver with this set to 1.6A for 500Lumens

The link below will show you an example of the effect I’m trying to create. (Couldn’t hotlink and show it here for some reason)

Due to the fact that the Fabry-Perot filter is essentially Lorentzian in shape, the cut-on and cut-off slopes are very shallow and the rate of attenuation in the out-of-band blocking range is very slow. To improve the slopes and increase the attenuation in the blocking band, we introduce more cavities into the construction. Please refer to the following charts for a comparison of one to four cavity filters and note that this data is only applicable to dielectric bandpass filters.

Another very important factor to note is that due to matching the different cavities within a filter construction, we cannot add an infinite amount of cavities. Please refer to the and custom interference filter section of this catalog for the appropriate information.

http://www.kaidomain.com/p/S024418.Cree-XM-L-T6-Neutral-White-5000K-5500K-with-18mm-x-18mm-Aluminum-Base Or XPL will be a little sharper http://www.kaidomain.com/p/S024472.Cree-XP-L-HI-V2-Neutral-White-4500K-LED-Emitter-with-KDLIGHT-3535-20-20mm-x-1_5mm-DTP-Copper-MCPCB

Band passfilter transfer function

You need an unobstructed light source. No lens no reflector to get a crisp shadow at that short 10-15cm distance. What we call a zoomie flashlight comes close but not at the short distance. I now tried a flashlight with no lens and no reflector and it casts a nice circle of light and has very crisp shadows of my hand on the ceiling, closer and further away than your requirements. You should be able to get it close to just the size of the steel plate.

1) Cree XP-E2 ‘Torch’ When driven at 2.2A (it can not be driven much higher) and well heatsinked, it puts out 500 lumen when dedomed. The led with dome is the same size as the led in your picture above, but it can be dedomed what makes it an even tinier source for even crisper shadows.

2) Osram Oslon Black Flat Driven at 3.5A it puts out 700 lumen. The led is already without dome, exact the same die size as the ‘Torch’

The metal-dielectric type is similar to the all-dielectric type except that it utilizes a metal spacer layer instead of a dielectric layer. Although this type of filter has excellent out-of-band blocking and high passband transmission, it lacks the sharp cut-on and cut-off slopes of the typical two and three cavity filters. The metal-dielectric type is mainly used for bandpass filters in the ultraviolet. However one version, the induced transmission type, is used as an additional blocking component when rejection is required to the far infrared.

Perhaps take the glass and reflector out of the 10W flood and see what happens. I have a couple 12V 10W in warm white here if you need me to give a try. No cool white on AC current here at home. I think the fuzzy shadow is from the glass reflecting back on the reflector and mimicking multiple light sources. If it works and you need brighter go with 20W. These lights are over rated so even a 20W is only about 13W actual.

Band passfilter PDF

Take a proper heatsink, use thermal glue to get the star on it. Use glue to seal off the 4 sides of the LED and the solder pads.

I forgot to mention that to get the mentioned performance, both leds need soldered onto a so-called DTP ledboard, which gives ultimate heatsinking. Make sure that your builder uses them! The Oslon officially does not fit the most used XP-type boards but you can succesfully solder them on there anyway.

Use the Buck driver set to 1.5A per emitter, you can wire all emitters in series if your power supply provide >4V per LED.

Best choice is probably something like a CREE XPL HI LED run at 2-3 amps mounted on a heatsink and attached to a power supply to allow it to be plugged into an outlet. Depending on how many amps you run it at, you could easily get 500-1000 lumens.

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Band passfilter circuit

The central wavelength of the all-dielectric Fabry-Perot filter will shift lower in wavelength with an increase in the incident angle. The amount of wavelength shift is dependent upon the incident angle and the effective index (N*) of the filter. This feature can be very useful in tuning a narrowband filter to the desired central wavelength. The following formula may be used to determine the wavelength shift of a filter in collimated light with incident angles up to 15 degrees:

What about using a reflector as well so light isn’t bouncing all over the place? You could set up a wide angle to cover the area where the cut outs are but it ensures that light isn’t bouncing around elsewhere.

As a general rule, the highly reflective side of the filter should always face the source of radiation. This minimizes the thermal load on the absorbing glass blocking components and epoxies, thereby extending the lifetime of the filter. Apart from reduction of thermal effects, filter orientation is without influence on the spectral characteristics.

The effects of temperature, optical path geometry and environmental conditions must be considered when selecting or specifying bandpass filters. All of our filters are designed to operate at 23°C in normal incidence collimated beams. Please consult with one of our technical sales representatives before specifying any off-normal conditions so that a filter best suited for your application can be designed.

Band passfilter formula

When a filter is used with non-collimated light such as convergent or divergent rays, the wavelength shift will appear somewhat less than that of collimated light at the same angle. In a cone of light only the central ray is normal to the surface and all others are increasingly off-angle. The resultant shift could be given by integrating the wavelength shift over the range of angles but this is a rather lengthy process. A good approximation of the shift can be made by using the previous formula and dividing the calculated shift by two. This will work in systems where the full cone angle is a maximum of 20°.

The only things that seem to be able to do the job are the cree xlamps. However I can’t seem to find that in any consumer product (such as a car bulb) as a single smd.

The center wavelength of an interference filter will shift linearly with changes in ambient temperature, therefore it is very important to specify the operating temperature when ordering. The wavelength shifts in the direction of the temperature change, up with a positive change and down with a negative change. This shift factor will vary depending upon the filter's initial center wavelength. Please refer to the following chart for the proper temperature coefficient.

I play a lot with lights (with very little tech knowledge though). I make thousands of lantern lights for parades and various bespoke (shonky) lights for my long exposure light painting photos. However I have become stumped with a project I have on at the minute…

Aha! I have someone doing exactly what I seem to spend hours of my life doing! I spend a huge amount of time shining lights through my peg basket. Flashlights with no lenses definitely give the right effect. I did pretty much dismantle the 10 w flood to see what was making it blurred. I think it’s just the width of the array itself (is that the right word?). It’s not in front of me now but I think it’s about 10 mm squared or so. That’s just too broad at the distances I’m needing.

Itsonlyme - thanks for your suggestion. My limited experimentation with reflectors has left me with blurred edges to the shadows, even though it throws more light forward. It’s as if the light is coming from a much broader source. The pin prick of light gives the crispest beam. I wonder if some combination of lenses might work, but that’s beyond my ken!

Bandstop filter

(All the ramblings below add up to this: I need a 500 (ish) lumen 1 smd light source in order to cast strong crisp shadows. Ideally something I dont have to build myself)

Bandpass filters are one of the simplest and most economical ways to transmit a well-defined band of light, and to reject all other unwanted radiation. Their design is essentially a thin film Fabry-Perot Interferometer formed by vacuum deposition techniques, and consists of two reflecting stacks, separated by an even-order spacer layer. Each one of these structures is referred to as a cavity, and some filters may contain as many as eight cavities. There are many different variations of the Fabry-Perot type bandpass filter, but for this catalog, we will only consider the all-dielectric and metal-dielectric type.

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To reduce the chance of damage due to thermal shock, we recommend a maximum operating temperature of 70°C, and a maximum temperature change of 5°C per minute.