Probably the most challenging part of buying a LED is ensuring it is bright enough for its intended purpose. It is the single biggest area of frustration with consumers.
For example, many people think it is a simple matter of swapping out the common 50w halogen you find in most homes with a similar looking LED bulb, as shown on the right, only to find out that the brightness is nowhere near the same. This leads to a lot of disappointment particularly when many websites selling these types of bulbs say "equivalen to a 50w halogen". It is simply incorrect.
The total amount of light emitted by a source is measured in lumens. A 50w halogen outputs around 800 - 900 lumens, which means an equivalent LED replacement must be at least 800 lumens for it to be considered a fair replacement. Usually these types of LED replacements as shown on the right will be around 280 lumens which makes for very dim lighting and a poor choice to replace your halogen. So if you decide you want to go down this path of replacement make sure you find a bulb that meets the minimum lumen requirements of your existing halogen bulb. There are not any MR16 bulbs we could recommend that would be a direct replacement, but as technology improves one day it may be possible.
If you are really keen to ensure you get a similar replacement buy yourself a digital light meter. They are a very cost effective way to measure the output of your lights. These light meters measure lux, the brightness over a particular area. For example if you wanted to achieving an illuminance of 500 lux in a kitchen home kitchen using a single fluorescent light you'd probably need an output of 1200 lumens. So the greater the area to you want to light up (lux) the bigger the number of lumens the light needs to produce. Standing about 1 meter under a 50W halogen will probably give you around 280 - 320 lux (roughly speaking).
The brightness efficiency is measured in the amount of lumens produced per watt of (LM/w) power used. For example, a LED downlight that was 50 LM/w would use 16 watts if its brightness was 800 lumens. The idea obviously is to try and get the maximum number of lumens per watt (the higher the number the more efficient).
One other thing we should mention. The lumen output or brightness of a light is also affected by its colour temperature. The warmer the lights the less lumen output. So a 1100 lumen Cool White LED will probably produce 850-900 lumens if it was Warm White.