I've been a regular visitor to Hong Kong since 2010 and just returned from
the worlds largest LED lighting show again in October. I import
commercial retrofits that are years ahead of what is available (or
"hawked") here in the US. As such, I have quality products and I'm aware
of the crap that is out there. My background is in lighting, electronics,
television and cinema and I'm well aware of color temperature and lumens.
Unfortunately, the customer whose heart is in the right place is usually a
victim in cases like you describe. The hacks that sell LED retrofit
by-and-large have no clue as to what options are available as they only
re-sell what some distributor (or DIY store) has in stock. There are
success stories but most likely they are due to dumb luck and not any
engineering. Don't get me started on their lack of optical knowledge,
lumens, color temperature or the relationship of rods and cones to pupil
lumens, CRI, and the horrible spectral response of HPS lamps. I have
relations with over 30 vendors in China and I can't tell you how cool and
well-made the lamps are becoming.

Here is a brief overview of light and the eye:

Cones and Photopic vision- The central part of the eye is the fovea that
is rich in a type of cells called 'cones'. Cones are responsible for color
vision and are involved in vision during bright light. This is called
Photopic vision.

Rods and Scotopic vision-Rods are sensitive to dim light and are active
during low light intensity conditions. Rods cannot perceive color. Vision
due to rods is 'black and white.'

Light measuring instruments measure Light intensity in Lumens -
considering only the response of the cones. Thus, the Lumens measured by a
light meter are also called Photopic Lumens.

In conditions of low light intensity entire vision is due to rod cells
(scotopic vision). In medium light intensity (conditions as are often
found under street lights and in homes) vision is called Mesopic vision
and is due to both rods and cones. Using 'Photopic Lumens' to describe
light intensity in such an area grossly underestimates the light intensity
as it totally ignores the contribution of rod cells to vision.

And I hate CFLs, too.

Yours truly,

Mr. Klay Anderson, D.A.,Q.B.E.

Interesting. I read that LPS street lighting is the most effectively
efficient lighting that there is in terms of (mesopic?) lumens per watt, as
the yellow colour lies close to the most sensitive frequency of the human
eye. For sure, the 40 watt LPS streetlights that were removed from my
village, to make way for some 45 watt high pressure discharge lamps with a
whiter output, were far - and I mean far - more effective at lighting the
street than these new ones, which produce harsh, sharply defined cones of
light, and leave pools of darkness between. One of the 'selling points' that
the local council published before the work was done, was that because the
light was 'whiter', colour rendition would be improved. That is actually not
true, because the overall light level that they produce, is not enough to
take your eye up into the colour perception range. They are also crap in
fog, compared to the LPS lamps that they replaced. To be honest, the yellow
light from LPS and golden light from HPS street lighting has never bothered
me. I've never really understood why colour rendition at night is of any
particular importance. Better I think that the air is 'saturated' with light
of any description, than to have lamps that produce concentrated 'patches'
of light that you might just about be able to see colour with, when you are
right underneath them.

I'm probably using wrong terms all over the place here, as I am no expert,
which clearly you are, but I'm sure you understand what I'm saying

Arfa