Economic advantage to using light shielding
Posted 01 May 2013 - 07:48 PM
Looking at light fixtures in my city(Shinagawa-ku, Tokyo), it seems that most street lights are not properly shielded.
The question I have is simple:
- How much does it cost to shield a street light (cost of equipment, cost of installation), and is there a cost decrease with scale (decrease of cost per light for each additional 100 lights done)?
- If a light is shielded (mercury or fluorescent bulbs), is it justified to diminish the intensity of the light? i.e. it does seem to make sense, since the light will then be fully directed downwards. BUT is there any further equipment to be installed to perform the intensity change? What would be the cost of such equipment?
- What is the wattage consumption of a standard street light (mercury or fluorescent) per night, how much would be spared by shielding and lowering the overall intensity?
In other words, I'm trying to get an idea about the economic advantages to shielding light fixtures (seems to be the very easiest to do with the least controversy) - that would be the only language that authorities would understand.
Posted 02 May 2013 - 02:47 AM
If a light is shielded (mercury or fluorescent bulbs), is it justified to diminish the intensity of the light?
If the interior of the shield is metalic and reflective and redirects the light to where it is useful, then yes you can theoretically reduce the bulb power to approaching 1/2 of the original (assuming the original wasn't over-bright for the intended application - if it was then you can reduce the lamp brighness substantially beyond 1/2)
What is the wattage consumption of a standard street light (mercury or fluorescent) per night,
You are asking for Watt hours? This is impossible to answer without reference to a particular lamp technology - incandesent, sodium, vapour (high and low pressure), mercury vapour, LED etc etc all are very different in power consumption for a reference level of brightness (assuming identical reflector unit amd measuring protocol)
However the economic equation is approximately the captital outlay of adding shield and changing the lamp to lower power unit versus electricity consumption saving in the lifetime of the lamp.
Adding a shield without reducing lamp power has no econnomic benefit. The benefit then is usually confined to limiting light trespass.
Right now the economomics may favour a complete exchange to a fully shielded LED unit (see http://www.bbc.co.uk...ology-22292129) as the power consumption is <10% of incandesent bulbs of same brightness and lamp lifetime is >>>>>> of an incandesent. The key factor in any exchange program is getting them to adopt a correctly shielded luminere - because once installed these units may last 20+ years!
Posted 17 May 2013 - 12:27 PM
Since the pitch for LED street lighting is a total-cost-of-ownership play, lack of maintenance plus low power consumption, LED lighting manufacturers are showcasing products that do direct the light toward the ground because it maximizes their competitive advantage -- using an inherently efficient light source in the most efficient and easily implemented way.
Posted 19 May 2013 - 06:50 PM