What Are Dichroic Color Filters?
Dichroic filters are circles of glass with a set of coatings that reflect certain colors (of light) and allow other colors to pass through.
For example, white light contains all colors in the visible light spectrum. If you pass that light through a blue dichroic filter, only the blue portion of the white light passes through while all the other colors are reflected back towards the light source.
The other way to change colors is to use tinted glass filters – these are less costly than dichroic filters but they absorb more light (are less efficient) and tend to fade with time.
How Are They Used?
- Dichroic Color Correction Filters. These are meant to shift the color temperature of white light to a light that is slightly more blue (cool) or yellow (warm). The resulting light is still considered “white” but it will have qualities slightly different from the original light – especially noticeable when viewed side-by-side. Color correction filters can be used for general area lighting or for prominent flood and spotlighting in a project.
- Dichroic Color Filters. These are filters with more saturated colors such as dark blue, indigo, orange, green and red. They are primarily used for holiday lighting or for special effects. Unlike color correction filters, these colors should not be used as primary area lighting, nor for floods or spots – unless a dramatic special effect is desired. These lights can, however, be used as backlights or accent lights that, when used with white light, provide dramatic, mysterious, or romantic effects. For example, a statue may be primarily lit from the front (fill light) with white light, then lit from the side (key light) with amber light, then lit from the back (backlight) with an indigo light. The key to making this a successful strategy is to make sure that the fill or key light is white – this allows the colored lights to provide a dramatic emphasis.
Will They Be Bright Enough?
This is an important question. Every color filter (regardless of type) reduces the quantity of light that passes through. There is no way to transform the entirety of a beam of white light into a beam of (for example) green light. A green dichroic filter works by reflecting (back into the fixture) all the non-green wavelengths of light and only allowing the green portion to pass through. If the initial proportion of green light was only 5% of the white spectrum then the resulting quantity of green light will only be 5% of the original. This is why the purer (saturated) the color, the greater reduction in perceived brightness. The resulting illumination will be beautiful, but may be less bright than anticipated and require a light source with higher lumen output.
Brightness is also dependent on what is being illuminated. Lighting a tree with dark-colored bark requires a much brighter light than lighting a light-colored object. The most saturated of the filters (such as red, green, and indigo) should only be used on light-colored objects.
It is highly recommended that designers test color filters on specific applications before they commit to purchasing the filters for a project – and to use fixtures with high lumen outputs.
Orientation and Insertion
- Install the filters with the dichroic-coated side facing the light source.
- These filters should only be used in fixtures indicated in the product description page of the specific filters.
- Before inserting the filters into the fixture, remove the plastic button on the center of the optics to get a better fit.
Will the Projected Light Show Uniform Color Across the Beam?
Some of the more saturated color dichroics show color shifts at the edge of the beam – all dichroics have this issue because the incident angle of the light source(s) determines the projected color.
Wider angle optics exhibit more color shift than do narrower optics since incident angles exiting the filter are wider. Having said this, the color shift (at the beam edges) in most cases is acceptable and may even be desirable since these saturated filters are mostly used to achieve dramatic effects.
The color shift can be minimized through use of an additional diffusion filter placed on top of the dichroic filter. We suggest trying the VOLT®’s Wide Spread Flood Filters (with Micro Lens Technology). Note that the use of this filter will reduce lumen output to a certain extent.
If the colors are used for architectural features, then the color shift at the edges may not be acceptable. Always test filters if you are unsure about the effects!
- Avoid depositing oil from your hands onto filters. Hold filters from the edges only.
- Blow loose dirt and particles from the surface of the filter using a lens puffer or canned air. If using canned air, blow the air at the lens from an oblique angle. Do not blow air from your mouth as you may deposit small particles.
- Apply isopropyl alcohol to a lint-free cotton swab or cloth and rub the filter’s surface in a circular motion, working from the center to edge. Gently apply pressure. Avoid rapid side-to-side motions.
- Use the puffer or canned air to evaporate excess alcohol from filter surfaces.
- Repeat steps 3 & 4 above using a clean, lint-free cotton swab with each cleaning until all surface contamination is removed.
- To complete the cleaning process wipe filter surface using lens paper gently applying pressure.
- Return your filter to the original plastic case or envelope provided.