T5 Adaptors and light levels
As a general guide, we advise clients that if they are happy with their current light levels with new T8 tubes and clean diffusers, they will almost certainly be happy with the light levels following conversion to T5 using the ME-T5 adaptor.
By the same principle, if light levels are insufficient for purpose with new T8 tubes and clean diffusers – then a T5 conversion isn’t the right lighting solution.
Click here to download T8 v T5 Light Comparison PDF
Historically, light has been measured using ‘lumens’, as measured by conventional lux meters. However, current thinking – no doubt driven by the increasing popularity of LED lighting – is that the lux levels recorded by a lux meter, tell only part of the story. It is now fairly common to read light output described in ‘initial design lumens’ and restated as ‘initial pupil lumens’.
The theory is that human eyes ‘see’ through light receptors called rods and cones. The cones respond to light in the yellow / green spectrum and the rods respond to light in the blue/ green spectrum. There are roughly ten times as many rods as there are cones – but a conventional lux meter only measures the light that the cones would respond to. That means that the lux meter is ignoring the majority of the light that you actually need to see clearly.
Two scientists – Dr Sam berman and Dr Don Jewett have developed a new measurement system – their work was supported by the US Energy Department – not by a lighting company trying to argue the case for LED lighting. Their research is the basis for the conversion ratio (P/S) that is used to convert ‘initial design lumens’ to ‘initial pupil lumens’.
Under the ‘Pupil lumen’ system – T5 lighting performs very well – and so does T8 lighting. However when taking into account the slightly better performance of the T5 lamps and their more stable lumen output over time, we believe that a T5 conversion is a sensible option to consider on the basis of cost effective light output.
“In the human eye the perceived brightness of illumination depends of color. It takes more energy in the blue or red portion of the color spectrum to create the same sensation of brightness as in the yellow-green region.
When it comes to sensing light in the human eye there are two main light-sensing cells called rods and cones. If one took a tube and looked straight ahead through it so that it allowed the field of view to be restricted 2 degrees, light photons would fall on the part of the eye called the fovea that consists mainly of cones. The peripheral area surrounding the fovea consists of both rods and cones with the rods outnumbering the cones about 10:1.
Cones have a peak response in the yellow-green region of about 555 nano-meters and rods have a peak response in the bluish-green area of about 505 nano-meters. Because both the rods and cones have been shown to have different sensitivities to colors they can be represented by two different sensitivity curves called Photopic Curves (representing the cone) and Scotopic Curves (representing the rod).”
Dick Erdmann
GE Specification Engineer
