FAQ - What to look for in an LED light

Lighting characteristics of particular interest to the user would include the directionality of the light emitted by the globe (intensity distribution), its total light output, its luminous efficacy (total lumens per watt,) color, its dimming compatibility, and longevity of the globe.

The directionality of a light source is important especially when retrofitting LED lights to replace naturally omni-directional incandescent bulbs. LEDs are inherently directional, however different bulb designs and clever use of diffusers by various LED globe manufacturers has largely overcome this issue, leading to uniform light emission and a seamless retrofit option. The intensity distribution graphs obtained for each test light maps the measured intensity (lux) to the measurement angle of the photometers sensor as it traces out a circumference centered about the light source. The results are represented on a polar graph where the radial distance from the centre is proportional to the measured intensity at the given angle.

Total light output of a light fixture is called the total luminous flux, which, expressed in lumens, represents the total visible light a lamp can produce (for the given wattage of the lamp), no matter what the intensity distributions are¹. Different rooms and intended visual tasks will require different levels of light. Bathrooms and indoor activity areas may require a lot of light, while dim, low power LED lights might be suitable for applications requiring low levels of light for long periods of time e.g. outdoor porch lights.

Derived from the total luminous flux of a light source and its wattage, the luminous efficacy of a lamp is concerned with energy saving and is the ratio of luminous flux to input power. When comparing the luminous efficacy of LED lamp products, it is important to keep in mind that it is easier to make an efficient 20mA LED, than an efficient 700mA LED.

Factors affecting the longevity of an LED light are discussed on the FAQ page LED Life Expectancy

References

¹ Basic concepts in photometry, radiometry and colorimetry, Handbook of Optoelectronics