Illuminance Levels
Many countries use standards and guidelines for the illuminance levels recommended for different spaces. These recommended values depend on many factors, including the type of lighting systems and the activities expected in the space. For example, the illuminance levels for task lighting with high accuracy activities are higher than the illuminance values for the ambient lighting. The values of illuminance level can be determined or recommended by other criteria.

The individual‘s preferences can be the main factors in the determination of the lighting level. Also the desire to give a certain impression of the space, such as celebration and happiness, may require a higher illuminance level in the space.

The differences in the illuminance levels depend significantly on the judgment of the lighting designer and on the architect's view. In general, any difference that has artistic value is acceptable as long as it meets the basic lighting concepts and recommendations of the lighting system. The design of these levels should not cause eyestrain or glare when the viewer looks at the different levels at the same time. For example, we can focus attention on the difference between the bright recessed downlight and the ceiling. In this case it is recommended to use a light- reflecting ceiling to reduce the impact of the brightness (luminance) of the fixtures on the eyes.

Color Perception
Color helps in the perception of the beauty of the interior design and in the adjustment of the occupant's mood. The perceived color of the surface is determined not only by the color of the surface, but also by the color of the light. Therefore, the type of lamp in the light fixture can significantly impact the perception of the color of the object. This effect should be taken into account when designing spaces such as show rooms and fitting rooms.

Color can impact the mood of the occupants; for example, bright and different colors in the same space illustrate happiness. On the other hand, a monotone and dark color may give the opposite impression. The character of the space may be altered by the color. For example, red gives the impression of warmth and blue-green gives the impression of coldness.

Objects and Shapes
The perception of the object's shape differs with the light distribution on its surface and with the configuration of the resulting shadows. The direction of the light beam can easily affect the perception of the object's shape as shown in the following figure.

Also, the directed angled light generates shadows; therefore it is essential to make a decision if these shadows are needed. Shadows will show the roughness of an imperfectly finished flat surface. Uniform lighting on these surfaces can be implemented. This approach should be used carefully because it can make a three dimensional object looks flat.

The combination of direct and uniform lighting is used in many cases. If the light is not uniform on the surface, different areas will appear to be at different distances. Therefore, to lighten the outer or the inner area of the flat surface will make this surface appear concave or convex as shown below.

Space and Dimensions
A high level of illuminance in the space can give the impression of large volume. To focus on the variety of internal design elements and to attract attention to specific spots in the space, the lighting systems shall include different illuminance levels or lighting styles. This approach is frequently used to isolate reception areas, stairs, exits, and waiting areas in the space.

If the lighting system includes linear ceiling fixtures, the effect will be the dimension enhancement in the direction of the lighting system as shown in the following drawing.

We can get the impression of a high ceiling by good illumination of the ceiling or the upper parts of the walls. Using the light or the light fixtures itself, we can easily focus attention on the routine elements in the interior design or make the opposite effect.

Light has an effect on the physical nature of the structure. Poor illumination of columns with a well-lighted ceiling deck will focus attention on the nature of the heavy columns (holder) and the lightweight deck. By applying the opposite lighting arrangements, a special artistic effect is generated from the impression of the distortion of the physical nature. Similar distortion results when illuminating the area between two components of the interior elements. Lighting the area between the column and the ceiling deck gives an impression that they are disconnected.

Lighting systems are used frequently to indicate the directions of the movement in the space. This lighting guide can be achieved easily by increasing the illuminance level in the area where people are expected to move. These areas include stairs, entrances, and most importantly, the hallways.