This page discusses ways to change the color of a light.

• General Theory
• Good Methods
  • Colored Lamps
  • Colored Plastic Filters
  • Dichroic Glass Filters
  • Gel Filters
  • Lamp Dip
• Hacks
  • Cellophane
• Bad Methods
  • Paint
  • Fingernail Polish

• Related Pages

Since the light starts out white, changing the color of the light is an exercise in subtractive color mixing. We must filter out the colors that we don't want, in order to keep the desired color.

Note that this is most effective and predictable when we start with incandescent lamps and other light sources with a broad visible spectrum output. Filtering broken-spectrum light can produce strange results, and filtering monochromatic light is just plain silly. If this disclaimer makes no sense, brush up on your physics.

So, coloring a beam of light just requires that we put a piece of something between the lamp and the thing that you are illuminating. The only complication is what kind of something to use.

No matter the exact type of the material, it will:

• transmit some part of the incoming light - this is your final colored light
• absorb some part of the incoming light
• reflect some part of the incoming light

The more primitive types of filters come in a few colors, with little additional information. The more sophisticated filters perform to documented Spectral Energy Distribution (S.E.D.) curves, published by the manufacturer.

This is the S.E.D. curve for Rosco's Roscolux #342 Rose Pink.

According to this S.E.D. curve, Roscolux #342:

• transmits approximately 40% of the violet and blue energy of the spectrum
• transmits approximately 75% of the orange and red energy
• blocks all energy in the yellow and green range
• overall, 16% of the light gets through

The S.E.D. curve not only indicates precisely the effect that the filter will achieve, but also provides some hints as to the lifetime of the filter. Dark green and dark blue filters usually burn out the fastest because they absorb energy from the red side of the spectrum, which usually includes infrared energy. Absorbing extra infrared energy causes the plastic to reach it's melting temperature faster. Even if the plastic doesn't melt, the heat may cause the dye to sublimate or decompose, changing the color of the light. When dark filters are needed, try choosing filters that transmit high amounts of the infrared range above 700 nm. If the S.E.D. curve doesn't go far beyond 700 nm, pick the filter that transmits the most light at the 700 nm end of the spectrum, hoping that it also transmits high levels of the infrared range above it.

Colored flood lamps are usually available to home construction supply stores like Home Depot, and are often available from department stores like Target around Christmas.

I have seen flood lights in the following colors:

• green
• blue
• red
• yellow

Plastic film materials differ, too. This is what Rosco uses for their Roscolux line.

material	softening point	melting point	typical thickness	extremely dark colors
polycarbonate	160°C	220°C	3 mils	3-5 mils
polyester	125°C	300°C	1.42 mils	2.5 mils

[The softening point is where the filter begins to show stress marks and breaks down. Rosco prefers to use polycarbonate because of its higher softening point. Some dyes are not compatible with polycarbonate and must be made with polyester.]

Gel filters are usually sold in large sheets that you cut to the size that you need. They are also available in tubes designed to fit over a fluorescent lamp. I have seen gel sheets in various sizes:

• 20" x 24" - Rosco
• 21" x 24" - Times Square Lighting
• 10" x 10" - Times Square Lighting

The good things about gel filters are:

• available in a huge number of colors
• designed to function well in the hostile environment of a lighting system
• the material is flexible enough to be rolled up
• the material is soft enough to be cut with scissors, knife, or a paper cutter
• you can stack several gels to get different colors (subtractive color mixing)

• you usually have to get them from dealers in theatre lighting or DJ supplies
• you usually have to buy a large sheet, even if you only need a small piece

Manufacturers of gel filters have sample swatch books containing small pieces of each color. If you can convince them that you might buy in quantity, you can probably get such a book free. Otherwise, you can buy a sample book.

Gel filters are not magical. You can melt or burn them if they are used with an extremely hot lamp. Picking the right combination of lamp, fixture, and gel can improve this situation.

Here's an approximation of the wide range of colors available from Times Square Lighting:

007 - PALE YELLOW	010 - MEDIUM YELLOW	101 - DARK YELLOW
102 - LIGHT AMBER	104 - DEEP AMBER	021 - GOLD AMBER
162 - BASTARD AMBER	004 - MED. BASTARD AMBER	022 - DARK AMBER
108 - ENGLISH ROSE	035 - LIGHT PINK	036 - MEDIUM PINK
111 - DARK PINK	107 - LIGHT ROSE	110 - MIDDLE ROSE
128 - BRIGHT PINK	332 - ROSE PINK	328 - FOLLIES PINK
339 - ROSE PURPLE	019 - FIRE RED	182 - LIGHT RED
106 - PRIMARY RED	027 - MEDIUM RED	046 - DARK MAGENTA
342 - SPECIAL LAVENDER	052 - LIGHT LAVENDER	343 - MEDIUM LAVENDER
349 - PALE BLUE	118 - LIGHT BLUE	068 - SKY BLUE
119 - DARK BLUE	126 - MAUVE	181 - CONGO BLUE
115 - PEACOCK BLUE	121 - EVERGREEN	122 - FERN GREEN
124 - DARK GREEN	017 - SURPRISE PEACH	202 - HALF CT BLUE
253 - FROST

Heat is the enemy of color filters. To prolong the life of a color filter:

• Increase the distance between the lamp and the filter.
• Never use a plastic filter directly in front of a lamp - allow an air gap for ventilation. Lighting fixtures that are intended for use with color filters, like PAR cans, will have some means of ventiltion built-in.

Some manufacturers of gel filters:

• Times Square Lighting
• Rosco
• Great American Marketing
• Lee

There are probably several outfits that make stuff like this, but the most famous is Rosco's Colorine, which was the first product that the company made, back in 1910. Colors are described as "brilliant and long lasting", but "not for permanent installations." Another reference suggests Colorine for use on incandescent lamps of 40W or less.

part number	color	Roscolux filter equivalent
07601	Cardinal Red	26
07602	Ruby Red	27
07603	Magenta	49
07604	Moonlight Blue	80
07605	Urban Blue	82
07607	Emerald Green	90
07610	Golden Amber	41
07615	Canary Yellow	15
07617	Clear

Colorine is only available in pints. It costs a little over $14/pint as of January 2004.

Because cellophane simply isn't intended for this purpose, there are problems that limit this approach:

• Cellophane might be made of anything nowadays. If you get it close to a hot lamp, it might melt, discolor, or burn.
• Cellophane usually isn't strongly colored. So it might color the light a little, but will have problems making a deep shade.

Nitrocellulose is the technical name for "gun cotton", and is explosive and/or highly flammable. In the early days of motion pictures, movies were printed on nitrocellulose-based "nitrate stock". The movie film could easily catch fire, either from a stray cigarette or from the hot lamp of the projector. Worse, as the film aged, it often became unstable.

Just to be sure, you should avoid attempting to color a lamp by applying fingernail polish.

• how color vision works
• color systems
• color mixing
• coloring light [this page]

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