Luminous efficacy (or light output per watt ) is a measure of the efficiency of a light source, such as a lamp or fixture. It indicates how much light (in lumens) a lamp produces for each watt of energy consumed. The higher the luminous efficacy, the more efficient the lamp is at converting energy (electricity) into visible light.
Formula for luminous efficacy:
Luminous Efficiency=Lumen (light output)Watt (energy consumption)\text{Luminous Efficiency} = \frac{\text{Lumen (light output)}} {\text{Watt (energy consumption)}}
Example:
If a lamp produces 800 lumens and uses 10 watts of energy, its luminous efficacy is: 800 lumens 10 watts = 80 lumens per watt (lm/W)\frac{800 \, \text{lumen}} {10 \, \text{watt}} = 80 \, \text{lumens per watt (lm/W)}
Light output and different lamps:
- Incandescent bulbs : These usually have a low luminous efficacy of around 10-15 lm/W , which means that a lot of energy is lost in the form of heat.
- Halogen lamps : Slightly more efficient than incandescent lamps, with a luminous efficacy of about 15-25 lm/W .
- Fluorescent lamps : These have a higher light output, typically between 40-100 lm/W .
- LED Lamps : LEDs are the most energy-efficient light sources and can achieve luminous efficacy levels of 80-150 lm/W or even higher, depending on the quality and technology.
Importance of light output:
- Energy Efficiency : A higher light output means that a bulb requires less energy to produce the same number of lumens (light), leading to lower energy costs and a smaller carbon footprint.
- Sustainability : Lamps with a high light output usually also have a longer lifespan, because they waste less energy in the form of heat.
- Cost savings : By choosing lamps with a high light output, you not only save on your energy costs, but you also contribute to a more sustainable use of energy sources.
In short, light output is a crucial factor when choosing lighting, especially if you're looking for energy-efficient solutions. It not only helps you save energy but also reduces your environmental impact.