Lumes per Watt
Most people confuse higher wattage for better lighting. While they are partially correct but it may not be economically correct since wattages are to measure power consumption while lumens are used for measuring brightness level of lighting fixture. So higher lumens per watt is better economically and better for your eyesight.
CRI - Colour ratio index
CRI (Color Rendering Index) is a measurement unit for lighting fixtures to understand how accurate is the colors of objects to human eys as they would appear under natural sunlight. CRI is an important factor in determining the quality of light generally measured upto a scale of 100. Anything above is regular while crossing 90 significantly increases the lighting fixture cost.
Lumens required for space
Use a thumb rule for calculating lumens in a room i.e. Length X Width X 22.5
So for room of 15ft by 10 ft would require 150×22.5 = 3375 lumens, if you have selected a lighting fixture that produces 120 lumens per watt then you would need around 28 – 30 watts of light spread across different parts of the room.
Keep in mind this is only a reference and the actual is totally based on application and a designers choice of setting up the rigth mood lighting.
Lighting applications as per need
While you can have a fair idea about the lumens required for a room through sampling a lighting fixture but it is extremely important to understand lighting moods to have adequate mix and match of different type of spotlights to get the desitred mood.
- Accent Lighting.
- Ambient Lighting.
- Decorative Lighting.
- Task Lighting.