Notably low pressure sodium is more lumens per watt than a typical LED.

The main energy saver is simply that the newer LED lights are dimmer!

Grombobulous 5 hours ago | parent | next [-]

You’re leaving out the part where the sodium lights wasted a lot of their lumens by tossing them into the sky. LEDs can be dimmer because they can be directionally controlled.

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OkayPhysicist 4 hours ago | parent [-]

That's trivially solved with a reflective housing, which nearly all sodium lamps I've ever seen had.

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linolevan 2 hours ago | parent [-]

While it is definitely true that original power drops were due to lower lumens, few things:

- reflective housing is super inefficient (~70% losses on the bounced light off typical material, at the top end expensive stuff still ~23%), still better than just losing the light upwards but not as many lumens on the road as a lab test would show

- Today LEDs are more efficient than sodium

Some math: 100W HPS cobra head lamp prdouces 9.5k lumens, including ballast it draws ~133W from the wall. Lab test shows about 70% of the lamp's light leaves the fixture (with the rest being lost in the housing) leading to ~7k lumens exiting. Roughly 53 lm/W.

LED cobra head lamps get like ~125 lm/W on the low end + fade much more slowly than sodium

	▲	OkayPhysicist an hour ago \| parent [-]
		Don't low-pressure sodium lamps get like >2x efficiency gains over HPS?

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throwaway198846 3 hours ago | parent | prev [-]

Why there weren't dimmer low pressure sodium lights?