The chemistry of color: Producing perfect hues with glass

There is a science – and a great deal of technology – behind illuminating a dark stage in a perfect red light, for example. A ruby red that floods a stage is the product of chemistry, optics, and glass manufacturing.

The products of this master light manipulation are everywhere, from the office copier to the research lab to theaters. Let’s look at how glass plays a role in reproducing the natural world’s color and light.

Creating nature’s true colors with glass

Lighting sets the mood. In performance halls around the world, the colors that flood the stage from overhead are just as important as the costumes and set pieces.

Picture a single green stage light for a moment, hanging in the rafters high above a stage. High intensity bulbs shine light down on singers, dancers, and actors. A color filter, set in front of the bulb, creates the green by restricting transmission of every other color in the spectrum. The only light passing through this filter floods the stage with a true green hue.

These filters, known as either dichroic or interference filters, are made of glass with several – less than 1 micrometer thin – functional coatings that reflect or absorb certain wavelengths and are capable of creating virtually any desired color hue. While the coating is mainly responsible for the color, the glass is the unheralded supporting actor. Not just any glass will do – it needs to be of high optical quality that results in clear and focused light, must be strong and robust enough to perform at the highest level in every show and able to deal with high operation temperatures or sudden thermal changes that occur when the high power stage lights are turned on.

Dichroic filters made of BOROFLOAT have excellent strength and color clarity.

The chemistry of the perfect color

BOROFLOAT®, SCHOTT’s floated borosilicate glass, is an ideal substrate for these types of applications. This strong and robust glass is just as important as the thin coatings that are manufactured onto it; BOROFLOAT’s excellent optical clarity ensures that the light passing through it is pure, and its thermal resistance makes it exceptionally resilient against warping, breaking and degrading after months or even years of nightly performances.

BOROFLOAT’s strength comes from its namesake, and the fifth element on the periodic table: boron. During melting, SCHOTT mixes boron and alumina with the traditional silica and other components, commonly used in glass production, to create a stronger, more rugged glass. Boron strengthens the chemical network of BOROFLOAT® while boosting its chemical and heat resistance. The glass’s low levels of iron and other impurities also increase its high light transmission and preserve its high optical quality.

Dichroic filters made of plastic will alter, can warp (causing light to shine unevenly on the stage) and eventually break down in the face of higher temperatures. And functional filters made of other glass types can break depending on thermal gradients – bad news when consistent and accurate color is needed.

Using BOROFLOAT glass with its exceptional thermal resistance has another huge advantage over solid solutions – flexibility. Tailored coating designs applied to SCHOTT’s borosilicate glass allow virtually any light hue to appear on stage – all conveniently applied to one robust substrate.

From space to stage, and beyond

Dichroic filters are a child of the 20^th century space race; NASA invented them not necessarily for their color changing properties, but because they are very radiation resistant, capable of protecting astronauts and their equipment on spaceships from heavy doses of harmful radiation.

Besides stage lighting, dichroic filters are also used in projectors to illuminate boardroom screens with perfect colors in every pixel. They can also be used in cameras, beam splitters in microscopes, and for architecture applications, like mood lighting.

Then there are hot and color mirrors, which can be found in everything from heat lamps (hot) to barcode scanners (cold). Hot mirrors reflect infrared light (heat) and transmit visible light, and are often used in halogen/HID lamps to increase filament temperatures for better efficiency and longer lifetimes. Capable of operating at high temperatures, hot mirrors are used in aerospace applications, heat/light separation, fiber optic lighting, medical and dental lighting, as well as LCD displays.

Cold mirrors, on the other hand, transmit infrared light but reflect visible light. They are used in dielectric mirrors in sensor technology, medical lighting, barcode readers and photocopiers.

Mastering the color wheel, and more

Spilling two primary colors together creates a new shade that looks great on canvas. Similar to an artist’s palette, dichroic filters “mix” and shine virtually any color onto stage – an often unnoticed but important set piece when illumination of attractions is required.

Dichroic filters help create those perfect reds, blues, and greens – and every color in between – at the world’s greatest theaters or to illuminate buildings, bridges or other architectural highlights. However, functional filters can do more than just capture nature’s best hues, which is why they’re used in everything from movie projectors to medical lighting.

Creating perfect, but artificial, color hues is a challenge of chemistry, optics, and thermal resistance and dichroic filters on SCHOTT’s borosilicate glass are generating midnight blues, cherry reds, and lettuce greens all around us. In other words, without BOROFLOAT®, the world would probably be a bit duller.