Start By Determining How Much Light You Need
The number and type of LEDs you select for your application depends on many factors, including:
- The size of the area to be illuminated
- The illuminance (brightness) that you need
- The light color that you need
Total lumens required is estimated by selecting a similar light source from the table below and multiply the value in the Lumens per Watt (LPW) column by the total wattage of your current lighting.
For example, if you are using two 12" fluorescent lamps rated at 8 watts each with a lumens output of 60 LPW, then you will need select LEDs that can generate 960 lumens to produce the same amount of light.
| Light Type |
LPW
|
|---|---|
| Incandescent Bulb |
12 - 18
|
| Halogen |
20
|
| Fluorescent Tubes |
50 - 100
|
| Metal Halide Lamp |
65 - 115
|
| High-Pressure Sodium Lamp |
85 - 150
|
| Low-Pressure Sodium Lamp |
100 - 200
|
Note that this table is for general reference only. The actual LPW rating for many types of light can vary by quite a bit. You may be able to find more accurate lumens ratings in your lighting documentation, or from the light manufacturer.
Once you have the total lumens output of your current system you can then estimate how many LEDs you will need by simply dividing the lumens rating of the LED you will be using by the lumens generated by your current system.
(W x LPW) / Ll = Ln
Where:
- W = Total wattage rating of the light being replaced.
- LPW = Lumens per Watt from the table above, or the manufacturer's documentation.
- Ll = Total lumens output of each LED or LED assembly you want to use.
- Ln = Total number of LEDs you will need to use to get an equal or better amount of light.
For example, if you are replacing a 40W Halogen lamp that has an LPW rating of 20 with an SP-01-W5 LED module that you will be powering at 700mA, then you will probably want to use 4 SP-01-W5 to replace the halogen lamp.
(40 x 20) / 235 = 3.4
This will only tell you how many LEDs you will need to generate an equal amount of light. There are other factors that can affect lighting including color temperature, beam angle, etc.