LEDs

I'll reproduce a little 'essay' on LED lighting that I wrote on a technical listserve today.

There has certainly been a lot of interest in LED lighting in the last
couple of years, with proponents spewing out the cost efficiency as
it's major plus point. In the last decade, improvements have been made
to colour rendition, effifacy(lumen to watt ratio), and cost. However,
there are a couple of major issues that remain when compared to other
light sources - capital costs and colour consistency. Both these
factors are closely correlated as the process to achieve the colour
consistency for any batch of LEDs is extremely difficult, resulting in
higher manufacturing costs. You can almost be assured at this current
moment that the cheaper LED fixtures will have less colour consistency
among each other, than a higher priced unit. Having said that, it is
cheaper to buy a 1 or 5 watt LED today than it was five years ago, but
colour consistency remains a major challenge in the industry.

Capital costs for installing LED fixtures is approximately three to ten
times higher than similar incandescent(tungsten, halogen) or high
intensity discharge(HID - metal halide, mercury or sodium discharge)
fixtures. There are a few reasons for this besides the higher
manufacturing cost as mentioned above. Other issues resulting in higher
cost include the narrow coverage and efficiency of the individual LEDs
- this results in a higher number of LEDs needed to cover a stated area
and to achieve a specified lighting level.

As an example, the cost of using LEDs is about 5 times higher than a
conventional design in one of my current architectural lighting
projects,. About 10-15% of the total cost is spent on procuring extra
spare LED stock in the same batch to ensure future replacement will
have the same colour consistency.

For lighting an auditorium, the cheapest method with the highest
efficiency would be to use HID type fixtures, followed by flourescent
or compact PL type lighting, with incandescent lighting coming in last.
However, the cheapest method is usually not ideal for the purposes of
auditorium type functions as colour temperature and dimming is usually
an operational requirement for these spaces. The only type of lighting
that can be dimmed without higher infrastructure costs is the
incandescent fixture. All other types of lighting will require
additional wiring infrastructure and additional equipment to achieve
dimming in a satisfactory manner. This will result in higher
installation costs, but there will be lower operational and maintenance
costs due to the lamp efficiency. For the moment, the exception is LED
fixtures - due to its higher installation cost, it will take a longer
period of time to recoup the capital costs compared to other type of
fixtures. In a nutshell, you will need a lot of LEDs to cover an auditorium, and still will not be able to get similar light output levels at this point in time, when compared to other types of lights.

For stage theatre lighting, LEDs have popped up as various incarnations
of the PAR64 or floodlight type fixtures, complete with colour mixing capabilities at
fairly attractive prices compared to other lighting methods. These
fixtures usually use the RGB(red, green, blue) method of colour mixing.
There are two methods to achieve this - tri-colour RGB, where the three
colours are integrated into a single LED, and a combination of
multiple numbers of RGB coloured LEDs into the fixture. The tri-colour
LEDs have the advantage of slightly higher output with no colour
fringing effects due to its point source characteristic. Again, the issue of
colour consistency pops up in the lower cost fixtures as these manufacturers generally purchase the lower quality LEDs. The colour
consistent and higher output fixtures such as the PixelPar may
cost as much as AUD3,500.00 per fixture, putting it out of the
financial reach of most theatres and churches.

Having said that, I would have no qualms using some of the cheaper
China-made LED par cans that come as low as AUD300.00 each to light up
the stage as colour effects and washes. They are also good for places
where getting adequate AC power supply is an issue, as these LED
fixtures have relatively low power consumption. I am currently
assembling a touring LED lighting system as most of the smaller
community halls that we go to do not have adequate three-phase power
supply. With this setup, I am able to run a bunch of LED Par cans from
a couple of 10 amp power points with a laptop for control. This is only
feasible if, colour consistency is not critical for your application.

There are some advantages to using LEDs - longer lifespan, lower
maintenance and energy costs, less heat generation, and smaller size.
With LEDs, I'm able to put lights in spaces that would have been
impossible with conventional fixtures. It is my opinion that efficient
LED lighting is still a luxury and a bit of an experiment for the
moment, although this will change in the coming years with improved
manufacturing processes.