Amazon.com offers Prime members the Philips 100-watt Equivalent A21 LED Light Bulb, model no. 432195, for $19.97 with free shipping. (Non-members can spend $35 to qualify for free shipping; otherwise, shipping adds $5.52) That's the lowest total price we could find by $11. This bulb puts out 1,680 lumens for a purported 23 years.

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