Author Topic: Energy saving feature for street lights  (Read 6355 times)
seansy59
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Re: Energy saving feature for street lights « Reply #15 on: February 07, 2011, 09:36:48 PM » Author: seansy59
Really, it just sounds like another thing that could go wrong inside of it. Streetlights come on when it gets dark, and when needed. I don't see why they would want to dim it.
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Medved
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Re: Energy saving feature for street lights « Reply #16 on: February 08, 2011, 05:00:33 PM » Author: Medved
i don't understand...
I guess it is related to "form 109" question:

There are two methods generally used with magnetic ballasts:
1) Ballast input voltage reduction. Work on all ballast without any form of regulation (so HX transformer or series choke reactor), where the actual power delivered to the lamp is dependent on the input voltage. When dimmed, the voltage is gradually in small steps (less then 5%/step, slower then 5%/5min, so the lamp can thermally adopt prior to further voltage reduction) decreased to ~85% (for 60% brightness). This method has many disadvantages (more likely lamp arc extinction, limited dimming range to name the two most important), but one big advantage: The dimmer can be one common for large group of fixtures, so individual fixtures are kept basic (even without PF capacitor, as the compensation is then adaptive in the dimmer box).

2) Ballast output impedance increase. Can be done on all magnetic ballasts, mostly in the form of extra reactive component (inductor on lag ballasts like series choke, HX, mag-reg; capacitor on lead ballasts, like CWA or CWI) serially connected with the lamp, on the full (undimmed) setting bypassed by the contact from the control unit. This extra impedance keep original OCV (only reduce the lamp current), so could be activated at once (having more levels would make the gear even too complex). his method has the big advantage of how deep the lamp could be dimmed (HPS down to 30%), but require the extra circuitry (impedance component, controller,...) to be inside each fixture, making them more complex.
But as it is way simpler then the feed voltage reduction, it is useful with small group of fixtures, where the common, but quite complex dimmer would not pay off.
Other option belonging to this category is assembling the ballast from multiple lower current rated ones, so when connected in parallel yield same characteristics as nominal full power ballast. By disconnecting some sections is then possible to reduce the lamp power. This is useful mainly for serial reactors, as for other types the setup would become too complex...

Electronic ballasts always use lamp power regulation, so dimming is done by altering the target value for the lamp power regulation block. As this mean only altering some resistive divider (or even constant in the firmware, so cheap to implement), many ballasts intended mainly for HPS do offer this feature as standard.
Of course cheap HF selfoscilating ballast designs regulated by ring core saturation can not be dimmed, as the lamp power is given by the feedback transformer core saturation (like in CFL's,...).
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AngryHorse
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Re: Energy saving feature for street lights « Reply #17 on: February 17, 2011, 06:06:44 PM » Author: AngryHorse
Would it not be better to have a twin lamp lantern with both lamps running, then turn one off at midnight with a `part night photocell`?
Just a thought ::)
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Medved
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Re: Energy saving feature for street lights « Reply #18 on: February 17, 2011, 11:21:13 PM » Author: Medved
Would it not be better to have a twin lamp lantern with both lamps running, then turn one off at midnight with a `part night photocell`?
Just a thought ::)

It would be more expensive to maintain (for low wattages the cost of one lamp is about the same regardless of the wattage, while lifetime of both measured in installed time would be about the same) and the efficacy in the "high" mode would be lower (mainly when the "high" mean usual 70W HPS, where 35W have ~30% lower efficacy then 70W).
But such photocell can be used (with serial reactor and/or electronic ballasts) directly to alter the ballast impedance (and/or the power setting of the electronic one), such photocell actually is a form of the "control unit" i mentioned earlier.
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AngryHorse
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Re: Energy saving feature for street lights « Reply #19 on: February 18, 2011, 04:23:13 AM » Author: AngryHorse
I can see why LED is looking favourable for street lighting now ;)
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Current: UK 230V, 50Hz
Power provider: e.on energy
Street lighting in our town: Philips UniStreet LED (gen 1)
Longest serving LED in service at home, (hour count): Energetic mini clear globe: 54,050 hrs @ 10/2/24

"Beauty fades, dumb is forever".......Judge Judy :D

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