LED Light Distribution
FAQ – LED Light Distribution
Distribution of light from any light fixture will vary. It’s an important consideration when manufacturing lights designated to a particular task. People might want a uniform light in an office, but a concentrated spotlight on their desk as well. Lights can be specially engineered to meet these needs, providing the appropriate lighting throughout a room or building.
LED lights are “point source” which means the light emitted from them does not expand and spread out a great deal, like a laser pointed to a wall. A fluorescent tube will spread light throughout a room, whereas an LED unit will extract its light from each individual light emitting diode. An Led might replace a fluorescent tube by arranging multiple LEDs in a line congruent with that of the fluorescent tube. LED fluorescent replacement tubes can be sealed in a frosted glass covering. This provides more reflected light, so will reduce the glare.
A flood light or streetlight can be designed to focus light over a certain area. Showing the lighting pattern is frequently done using a “polar diagram” like the one shown below. Lighting may be shown also in iso-charts, showing the levels of light. The diagram will immediately tell us what direction the light is flowing in, and how bright the light is at different points of its trajectory.
We usually see Light distributed in the shape of a cone, or combination of combs such as in the above diagram which is known as “batwing” light distribution.
Planning Lighting Diagrams
Every light fixture, or luminaire as they are technically called can be described using an IAS file – industry standard files that supply all the necessary information to model the light distribution.
The free Dialux Software models this luminaire data, the building dimensions and a full lighting diagram can be modeled; allowing 3D animation prior to any light installation.
The example below is a simple warehouse, 18m x 24m. Ceiling height is 5m at the edges, and 8m in the centre. In this case there are 6 LED high bay lights at 150W around the edge and 3 x 200W LED lights in the centre. Light levels for this were to be >300 lx in the work areas. The software calculates out that the lowest light will be 240 around the edge of the building, but up to 480 lx underneath the centre edge lights.
For each surface, both the direct average illuminance and also indirect illuminance has to be calculated based on reflection factors and average luminance. The software will also provide rendered 3d images.