Once you understand the basic components of ADA signage, consider this product introduced in the 2010 ADA Standards-the dual-purpose sign.
The dual-purpose sign utilizes a new provision in the standard that says you can provide the main message of a sign in two different formats-one for the person who is completely blind and the other for those who need certain conditions in order to read signs visually.
The standard allows those two corresponding messages to be included on one sign blank or to be in two completely different signs. You could place the visual sign directly on a wall or door, with the tactile sign adjacent to the door in the legally required location. You could even put clear raised characters right on top of printed visual characters.
The dual-purpose sign is different from the original ADAAG with one set of characters for both visual and tactile readers after research showing that people who read by touch and those who read visually need different types of characters to read easily and accurately. People who read visually benefit from upper and lower case text and they need larger characters with bolder strokes. Dark to light contrast is vital to them, along with non-glare surfaces.
The new standard also addresses color deficiencies. Many safety signs and transit signs use red and black, which are virtually invisible for people with a certain form of color blindness. This is because the darkness of the two colors is so similar, it is difficult to distinguish them if you can’t see red.
People ask how they know which colors are light and which are dark, since there isn’t any guidance in the code. The best way to do it, according to most scientists dealing with the topic, is by looking at the light reflectance value (LRV) of each color. You can now purchase a portable instrument for $500 or less to measure the LRV, and in many cases, if you are using a colored material or a paint, the manufacturer will gladly supply it.
Once you know the LRVs of two colors you want to use, the simplest thing is to be sure that the two numbers are as far apart as possible. If the light color is in the top half of the scale (50-100) and the dark color is 15 or less, you will have minimum adequate contrast according to many building codes. Some studies have shown that a 70-point difference will provide quite good contrast for over 90 percent of people with serious vision conditions.
-Sharon Toji, “ADA Sign Lady”